2490 lines
78 KiB
Rust
2490 lines
78 KiB
Rust
//! Optional values.
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//!
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//! Type [`Option`] represents an optional value: every [`Option`]
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//! is either [`Some`] and contains a value, or [`None`], and
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//! does not. [`Option`] types are very common in Rust code, as
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//! they have a number of uses:
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//!
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//! * Initial values
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//! * Return values for functions that are not defined
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//! over their entire input range (partial functions)
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//! * Return value for otherwise reporting simple errors, where [`None`] is
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//! returned on error
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//! * Optional struct fields
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//! * Struct fields that can be loaned or "taken"
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//! * Optional function arguments
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//! * Nullable pointers
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//! * Swapping things out of difficult situations
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//!
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//! [`Option`]s are commonly paired with pattern matching to query the presence
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//! of a value and take action, always accounting for the [`None`] case.
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//!
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//! ```
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//! fn divide(numerator: f64, denominator: f64) -> Option<f64> {
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//! if denominator == 0.0 {
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//! None
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//! } else {
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//! Some(numerator / denominator)
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//! }
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//! }
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//!
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//! // The return value of the function is an option
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//! let result = divide(2.0, 3.0);
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//!
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//! // Pattern match to retrieve the value
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//! match result {
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//! // The division was valid
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//! Some(x) => println!("Result: {x}"),
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//! // The division was invalid
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//! None => println!("Cannot divide by 0"),
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//! }
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//! ```
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//!
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//
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// FIXME: Show how `Option` is used in practice, with lots of methods
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//
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//! # Options and pointers ("nullable" pointers)
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//!
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//! Rust's pointer types must always point to a valid location; there are
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//! no "null" references. Instead, Rust has *optional* pointers, like
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//! the optional owned box, <code>[Option]<[Box\<T>]></code>.
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//!
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//! [Box\<T>]: ../../std/boxed/struct.Box.html
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//!
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//! The following example uses [`Option`] to create an optional box of
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//! [`i32`]. Notice that in order to use the inner [`i32`] value, the
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//! `check_optional` function first needs to use pattern matching to
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//! determine whether the box has a value (i.e., it is [`Some(...)`][`Some`]) or
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//! not ([`None`]).
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//!
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//! ```
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//! let optional = None;
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//! check_optional(optional);
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//!
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//! let optional = Some(Box::new(9000));
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//! check_optional(optional);
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//!
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//! fn check_optional(optional: Option<Box<i32>>) {
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//! match optional {
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//! Some(p) => println!("has value {p}"),
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//! None => println!("has no value"),
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//! }
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//! }
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//! ```
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//!
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//! # The question mark operator, `?`
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//!
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//! Similar to the [`Result`] type, when writing code that calls many functions that return the
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//! [`Option`] type, handling `Some`/`None` can be tedious. The question mark
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//! operator, [`?`], hides some of the boilerplate of propagating values
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//! up the call stack.
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//!
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//! It replaces this:
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//!
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//! ```
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//! # #![allow(dead_code)]
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//! fn add_last_numbers(stack: &mut Vec<i32>) -> Option<i32> {
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//! let a = stack.pop();
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//! let b = stack.pop();
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//!
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//! match (a, b) {
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//! (Some(x), Some(y)) => Some(x + y),
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//! _ => None,
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//! }
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//! }
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//!
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//! ```
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//!
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//! With this:
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//!
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//! ```
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//! # #![allow(dead_code)]
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//! fn add_last_numbers(stack: &mut Vec<i32>) -> Option<i32> {
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//! Some(stack.pop()? + stack.pop()?)
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//! }
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//! ```
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//!
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//! *It's much nicer!*
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//!
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//! Ending the expression with [`?`] will result in the [`Some`]'s unwrapped value, unless the
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//! result is [`None`], in which case [`None`] is returned early from the enclosing function.
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//!
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//! [`?`] can be used in functions that return [`Option`] because of the
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//! early return of [`None`] that it provides.
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//!
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//! [`?`]: crate::ops::Try
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//! [`Some`]: Some
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//! [`None`]: None
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//!
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//! # Representation
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//!
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//! Rust guarantees to optimize the following types `T` such that
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//! [`Option<T>`] has the same size as `T`:
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//!
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//! * [`Box<U>`]
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//! * `&U`
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//! * `&mut U`
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//! * `fn`, `extern "C" fn`[^extern_fn]
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//! * [`num::NonZero*`]
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//! * [`ptr::NonNull<U>`]
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//! * `#[repr(transparent)]` struct around one of the types in this list.
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//!
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//! [^extern_fn]: this remains true for any other ABI: `extern "abi" fn` (_e.g._, `extern "system" fn`)
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//!
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//! [`Box<U>`]: ../../std/boxed/struct.Box.html
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//! [`num::NonZero*`]: crate::num
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//! [`ptr::NonNull<U>`]: crate::ptr::NonNull
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//!
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//! This is called the "null pointer optimization" or NPO.
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//!
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//! It is further guaranteed that, for the cases above, one can
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//! [`mem::transmute`] from all valid values of `T` to `Option<T>` and
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//! from `Some::<T>(_)` to `T` (but transmuting `None::<T>` to `T`
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//! is undefined behaviour).
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//!
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//! # Method overview
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//!
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//! In addition to working with pattern matching, [`Option`] provides a wide
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//! variety of different methods.
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//!
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//! ## Querying the variant
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//!
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//! The [`is_some`] and [`is_none`] methods return [`true`] if the [`Option`]
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//! is [`Some`] or [`None`], respectively.
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//!
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//! [`is_none`]: Option::is_none
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//! [`is_some`]: Option::is_some
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//!
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//! ## Adapters for working with references
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//!
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//! * [`as_ref`] converts from <code>[&][][Option]\<T></code> to <code>[Option]<[&]T></code>
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//! * [`as_mut`] converts from <code>[&mut] [Option]\<T></code> to <code>[Option]<[&mut] T></code>
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//! * [`as_deref`] converts from <code>[&][][Option]\<T></code> to
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//! <code>[Option]<[&]T::[Target]></code>
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//! * [`as_deref_mut`] converts from <code>[&mut] [Option]\<T></code> to
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//! <code>[Option]<[&mut] T::[Target]></code>
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//! * [`as_pin_ref`] converts from <code>[Pin]<[&][][Option]\<T>></code> to
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//! <code>[Option]<[Pin]<[&]T>></code>
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//! * [`as_pin_mut`] converts from <code>[Pin]<[&mut] [Option]\<T>></code> to
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//! <code>[Option]<[Pin]<[&mut] T>></code>
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//!
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//! [&]: reference "shared reference"
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//! [&mut]: reference "mutable reference"
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//! [Target]: Deref::Target "ops::Deref::Target"
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//! [`as_deref`]: Option::as_deref
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//! [`as_deref_mut`]: Option::as_deref_mut
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//! [`as_mut`]: Option::as_mut
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//! [`as_pin_mut`]: Option::as_pin_mut
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//! [`as_pin_ref`]: Option::as_pin_ref
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//! [`as_ref`]: Option::as_ref
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//!
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//! ## Extracting the contained value
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//!
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//! These methods extract the contained value in an [`Option<T>`] when it
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//! is the [`Some`] variant. If the [`Option`] is [`None`]:
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//!
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//! * [`expect`] panics with a provided custom message
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//! * [`unwrap`] panics with a generic message
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//! * [`unwrap_or`] returns the provided default value
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//! * [`unwrap_or_default`] returns the default value of the type `T`
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//! (which must implement the [`Default`] trait)
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//! * [`unwrap_or_else`] returns the result of evaluating the provided
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//! function
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//!
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//! [`expect`]: Option::expect
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//! [`unwrap`]: Option::unwrap
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//! [`unwrap_or`]: Option::unwrap_or
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//! [`unwrap_or_default`]: Option::unwrap_or_default
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//! [`unwrap_or_else`]: Option::unwrap_or_else
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//!
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//! ## Transforming contained values
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//!
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//! These methods transform [`Option`] to [`Result`]:
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//!
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//! * [`ok_or`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to
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//! [`Err(err)`] using the provided default `err` value
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//! * [`ok_or_else`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to
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//! a value of [`Err`] using the provided function
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//! * [`transpose`] transposes an [`Option`] of a [`Result`] into a
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//! [`Result`] of an [`Option`]
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//!
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//! [`Err(err)`]: Err
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//! [`Ok(v)`]: Ok
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//! [`Some(v)`]: Some
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//! [`ok_or`]: Option::ok_or
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//! [`ok_or_else`]: Option::ok_or_else
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//! [`transpose`]: Option::transpose
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//!
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//! These methods transform the [`Some`] variant:
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//!
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//! * [`filter`] calls the provided predicate function on the contained
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//! value `t` if the [`Option`] is [`Some(t)`], and returns [`Some(t)`]
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//! if the function returns `true`; otherwise, returns [`None`]
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//! * [`flatten`] removes one level of nesting from an
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//! [`Option<Option<T>>`]
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//! * [`map`] transforms [`Option<T>`] to [`Option<U>`] by applying the
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//! provided function to the contained value of [`Some`] and leaving
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//! [`None`] values unchanged
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//!
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//! [`Some(t)`]: Some
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//! [`filter`]: Option::filter
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//! [`flatten`]: Option::flatten
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//! [`map`]: Option::map
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//!
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//! These methods transform [`Option<T>`] to a value of a possibly
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//! different type `U`:
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//!
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//! * [`map_or`] applies the provided function to the contained value of
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//! [`Some`], or returns the provided default value if the [`Option`] is
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//! [`None`]
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//! * [`map_or_else`] applies the provided function to the contained value
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//! of [`Some`], or returns the result of evaluating the provided
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//! fallback function if the [`Option`] is [`None`]
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//!
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//! [`map_or`]: Option::map_or
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//! [`map_or_else`]: Option::map_or_else
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//!
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//! These methods combine the [`Some`] variants of two [`Option`] values:
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//!
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//! * [`zip`] returns [`Some((s, o))`] if `self` is [`Some(s)`] and the
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//! provided [`Option`] value is [`Some(o)`]; otherwise, returns [`None`]
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//! * [`zip_with`] calls the provided function `f` and returns
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//! [`Some(f(s, o))`] if `self` is [`Some(s)`] and the provided
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//! [`Option`] value is [`Some(o)`]; otherwise, returns [`None`]
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//!
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//! [`Some(f(s, o))`]: Some
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//! [`Some(o)`]: Some
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//! [`Some(s)`]: Some
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//! [`Some((s, o))`]: Some
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//! [`zip`]: Option::zip
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//! [`zip_with`]: Option::zip_with
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//!
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//! ## Boolean operators
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//!
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//! These methods treat the [`Option`] as a boolean value, where [`Some`]
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//! acts like [`true`] and [`None`] acts like [`false`]. There are two
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//! categories of these methods: ones that take an [`Option`] as input, and
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//! ones that take a function as input (to be lazily evaluated).
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//!
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//! The [`and`], [`or`], and [`xor`] methods take another [`Option`] as
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//! input, and produce an [`Option`] as output. Only the [`and`] method can
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//! produce an [`Option<U>`] value having a different inner type `U` than
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//! [`Option<T>`].
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//!
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//! | method | self | input | output |
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//! |---------|-----------|-----------|-----------|
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//! | [`and`] | `None` | (ignored) | `None` |
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//! | [`and`] | `Some(x)` | `None` | `None` |
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//! | [`and`] | `Some(x)` | `Some(y)` | `Some(y)` |
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//! | [`or`] | `None` | `None` | `None` |
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//! | [`or`] | `None` | `Some(y)` | `Some(y)` |
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//! | [`or`] | `Some(x)` | (ignored) | `Some(x)` |
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//! | [`xor`] | `None` | `None` | `None` |
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//! | [`xor`] | `None` | `Some(y)` | `Some(y)` |
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//! | [`xor`] | `Some(x)` | `None` | `Some(x)` |
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//! | [`xor`] | `Some(x)` | `Some(y)` | `None` |
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//!
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//! [`and`]: Option::and
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//! [`or`]: Option::or
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//! [`xor`]: Option::xor
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//!
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//! The [`and_then`] and [`or_else`] methods take a function as input, and
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//! only evaluate the function when they need to produce a new value. Only
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//! the [`and_then`] method can produce an [`Option<U>`] value having a
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//! different inner type `U` than [`Option<T>`].
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//!
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//! | method | self | function input | function result | output |
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//! |--------------|-----------|----------------|-----------------|-----------|
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//! | [`and_then`] | `None` | (not provided) | (not evaluated) | `None` |
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//! | [`and_then`] | `Some(x)` | `x` | `None` | `None` |
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//! | [`and_then`] | `Some(x)` | `x` | `Some(y)` | `Some(y)` |
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//! | [`or_else`] | `None` | (not provided) | `None` | `None` |
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//! | [`or_else`] | `None` | (not provided) | `Some(y)` | `Some(y)` |
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//! | [`or_else`] | `Some(x)` | (not provided) | (not evaluated) | `Some(x)` |
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//!
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//! [`and_then`]: Option::and_then
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//! [`or_else`]: Option::or_else
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//!
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//! This is an example of using methods like [`and_then`] and [`or`] in a
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//! pipeline of method calls. Early stages of the pipeline pass failure
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//! values ([`None`]) through unchanged, and continue processing on
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//! success values ([`Some`]). Toward the end, [`or`] substitutes an error
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//! message if it receives [`None`].
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//!
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//! ```
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//! # use std::collections::BTreeMap;
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//! let mut bt = BTreeMap::new();
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//! bt.insert(20u8, "foo");
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//! bt.insert(42u8, "bar");
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//! let res = [0u8, 1, 11, 200, 22]
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//! .into_iter()
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//! .map(|x| {
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//! // `checked_sub()` returns `None` on error
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//! x.checked_sub(1)
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//! // same with `checked_mul()`
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//! .and_then(|x| x.checked_mul(2))
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//! // `BTreeMap::get` returns `None` on error
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//! .and_then(|x| bt.get(&x))
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//! // Substitute an error message if we have `None` so far
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//! .or(Some(&"error!"))
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//! .copied()
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//! // Won't panic because we unconditionally used `Some` above
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//! .unwrap()
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//! })
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//! .collect::<Vec<_>>();
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//! assert_eq!(res, ["error!", "error!", "foo", "error!", "bar"]);
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//! ```
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//!
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//! ## Comparison operators
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//!
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//! If `T` implements [`PartialOrd`] then [`Option<T>`] will derive its
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//! [`PartialOrd`] implementation. With this order, [`None`] compares as
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//! less than any [`Some`], and two [`Some`] compare the same way as their
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//! contained values would in `T`. If `T` also implements
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//! [`Ord`], then so does [`Option<T>`].
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//!
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//! ```
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//! assert!(None < Some(0));
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//! assert!(Some(0) < Some(1));
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//! ```
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//!
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//! ## Iterating over `Option`
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//!
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//! An [`Option`] can be iterated over. This can be helpful if you need an
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//! iterator that is conditionally empty. The iterator will either produce
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//! a single value (when the [`Option`] is [`Some`]), or produce no values
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//! (when the [`Option`] is [`None`]). For example, [`into_iter`] acts like
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//! [`once(v)`] if the [`Option`] is [`Some(v)`], and like [`empty()`] if
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//! the [`Option`] is [`None`].
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//!
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//! [`Some(v)`]: Some
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//! [`empty()`]: crate::iter::empty
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//! [`once(v)`]: crate::iter::once
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//!
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//! Iterators over [`Option<T>`] come in three types:
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//!
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//! * [`into_iter`] consumes the [`Option`] and produces the contained
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//! value
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//! * [`iter`] produces an immutable reference of type `&T` to the
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//! contained value
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//! * [`iter_mut`] produces a mutable reference of type `&mut T` to the
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//! contained value
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//!
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//! [`into_iter`]: Option::into_iter
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//! [`iter`]: Option::iter
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//! [`iter_mut`]: Option::iter_mut
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//!
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//! An iterator over [`Option`] can be useful when chaining iterators, for
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//! example, to conditionally insert items. (It's not always necessary to
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//! explicitly call an iterator constructor: many [`Iterator`] methods that
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//! accept other iterators will also accept iterable types that implement
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//! [`IntoIterator`], which includes [`Option`].)
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//!
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//! ```
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//! let yep = Some(42);
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//! let nope = None;
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//! // chain() already calls into_iter(), so we don't have to do so
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//! let nums: Vec<i32> = (0..4).chain(yep).chain(4..8).collect();
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//! assert_eq!(nums, [0, 1, 2, 3, 42, 4, 5, 6, 7]);
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//! let nums: Vec<i32> = (0..4).chain(nope).chain(4..8).collect();
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//! assert_eq!(nums, [0, 1, 2, 3, 4, 5, 6, 7]);
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//! ```
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//!
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//! One reason to chain iterators in this way is that a function returning
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//! `impl Iterator` must have all possible return values be of the same
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//! concrete type. Chaining an iterated [`Option`] can help with that.
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//!
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//! ```
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//! fn make_iter(do_insert: bool) -> impl Iterator<Item = i32> {
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//! // Explicit returns to illustrate return types matching
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//! match do_insert {
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//! true => return (0..4).chain(Some(42)).chain(4..8),
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//! false => return (0..4).chain(None).chain(4..8),
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//! }
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//! }
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//! println!("{:?}", make_iter(true).collect::<Vec<_>>());
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//! println!("{:?}", make_iter(false).collect::<Vec<_>>());
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//! ```
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//!
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//! If we try to do the same thing, but using [`once()`] and [`empty()`],
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//! we can't return `impl Iterator` anymore because the concrete types of
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//! the return values differ.
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//!
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//! [`empty()`]: crate::iter::empty
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//! [`once()`]: crate::iter::once
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//!
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//! ```compile_fail,E0308
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//! # use std::iter::{empty, once};
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//! // This won't compile because all possible returns from the function
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//! // must have the same concrete type.
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//! fn make_iter(do_insert: bool) -> impl Iterator<Item = i32> {
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//! // Explicit returns to illustrate return types not matching
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//! match do_insert {
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//! true => return (0..4).chain(once(42)).chain(4..8),
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//! false => return (0..4).chain(empty()).chain(4..8),
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//! }
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//! }
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//! ```
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//!
|
|
//! ## Collecting into `Option`
|
|
//!
|
|
//! [`Option`] implements the [`FromIterator`][impl-FromIterator] trait,
|
|
//! which allows an iterator over [`Option`] values to be collected into an
|
|
//! [`Option`] of a collection of each contained value of the original
|
|
//! [`Option`] values, or [`None`] if any of the elements was [`None`].
|
|
//!
|
|
//! [impl-FromIterator]: Option#impl-FromIterator%3COption%3CA%3E%3E-for-Option%3CV%3E
|
|
//!
|
|
//! ```
|
|
//! let v = [Some(2), Some(4), None, Some(8)];
|
|
//! let res: Option<Vec<_>> = v.into_iter().collect();
|
|
//! assert_eq!(res, None);
|
|
//! let v = [Some(2), Some(4), Some(8)];
|
|
//! let res: Option<Vec<_>> = v.into_iter().collect();
|
|
//! assert_eq!(res, Some(vec![2, 4, 8]));
|
|
//! ```
|
|
//!
|
|
//! [`Option`] also implements the [`Product`][impl-Product] and
|
|
//! [`Sum`][impl-Sum] traits, allowing an iterator over [`Option`] values
|
|
//! to provide the [`product`][Iterator::product] and
|
|
//! [`sum`][Iterator::sum] methods.
|
|
//!
|
|
//! [impl-Product]: Option#impl-Product%3COption%3CU%3E%3E-for-Option%3CT%3E
|
|
//! [impl-Sum]: Option#impl-Sum%3COption%3CU%3E%3E-for-Option%3CT%3E
|
|
//!
|
|
//! ```
|
|
//! let v = [None, Some(1), Some(2), Some(3)];
|
|
//! let res: Option<i32> = v.into_iter().sum();
|
|
//! assert_eq!(res, None);
|
|
//! let v = [Some(1), Some(2), Some(21)];
|
|
//! let res: Option<i32> = v.into_iter().product();
|
|
//! assert_eq!(res, Some(42));
|
|
//! ```
|
|
//!
|
|
//! ## Modifying an [`Option`] in-place
|
|
//!
|
|
//! These methods return a mutable reference to the contained value of an
|
|
//! [`Option<T>`]:
|
|
//!
|
|
//! * [`insert`] inserts a value, dropping any old contents
|
|
//! * [`get_or_insert`] gets the current value, inserting a provided
|
|
//! default value if it is [`None`]
|
|
//! * [`get_or_insert_default`] gets the current value, inserting the
|
|
//! default value of type `T` (which must implement [`Default`]) if it is
|
|
//! [`None`]
|
|
//! * [`get_or_insert_with`] gets the current value, inserting a default
|
|
//! computed by the provided function if it is [`None`]
|
|
//!
|
|
//! [`get_or_insert`]: Option::get_or_insert
|
|
//! [`get_or_insert_default`]: Option::get_or_insert_default
|
|
//! [`get_or_insert_with`]: Option::get_or_insert_with
|
|
//! [`insert`]: Option::insert
|
|
//!
|
|
//! These methods transfer ownership of the contained value of an
|
|
//! [`Option`]:
|
|
//!
|
|
//! * [`take`] takes ownership of the contained value of an [`Option`], if
|
|
//! any, replacing the [`Option`] with [`None`]
|
|
//! * [`replace`] takes ownership of the contained value of an [`Option`],
|
|
//! if any, replacing the [`Option`] with a [`Some`] containing the
|
|
//! provided value
|
|
//!
|
|
//! [`replace`]: Option::replace
|
|
//! [`take`]: Option::take
|
|
//!
|
|
//! # Examples
|
|
//!
|
|
//! Basic pattern matching on [`Option`]:
|
|
//!
|
|
//! ```
|
|
//! let msg = Some("howdy");
|
|
//!
|
|
//! // Take a reference to the contained string
|
|
//! if let Some(m) = &msg {
|
|
//! println!("{}", *m);
|
|
//! }
|
|
//!
|
|
//! // Remove the contained string, destroying the Option
|
|
//! let unwrapped_msg = msg.unwrap_or("default message");
|
|
//! ```
|
|
//!
|
|
//! Initialize a result to [`None`] before a loop:
|
|
//!
|
|
//! ```
|
|
//! enum Kingdom { Plant(u32, &'static str), Animal(u32, &'static str) }
|
|
//!
|
|
//! // A list of data to search through.
|
|
//! let all_the_big_things = [
|
|
//! Kingdom::Plant(250, "redwood"),
|
|
//! Kingdom::Plant(230, "noble fir"),
|
|
//! Kingdom::Plant(229, "sugar pine"),
|
|
//! Kingdom::Animal(25, "blue whale"),
|
|
//! Kingdom::Animal(19, "fin whale"),
|
|
//! Kingdom::Animal(15, "north pacific right whale"),
|
|
//! ];
|
|
//!
|
|
//! // We're going to search for the name of the biggest animal,
|
|
//! // but to start with we've just got `None`.
|
|
//! let mut name_of_biggest_animal = None;
|
|
//! let mut size_of_biggest_animal = 0;
|
|
//! for big_thing in &all_the_big_things {
|
|
//! match *big_thing {
|
|
//! Kingdom::Animal(size, name) if size > size_of_biggest_animal => {
|
|
//! // Now we've found the name of some big animal
|
|
//! size_of_biggest_animal = size;
|
|
//! name_of_biggest_animal = Some(name);
|
|
//! }
|
|
//! Kingdom::Animal(..) | Kingdom::Plant(..) => ()
|
|
//! }
|
|
//! }
|
|
//!
|
|
//! match name_of_biggest_animal {
|
|
//! Some(name) => println!("the biggest animal is {name}"),
|
|
//! None => println!("there are no animals :("),
|
|
//! }
|
|
//! ```
|
|
|
|
#![stable(feature = "rust1", since = "1.0.0")]
|
|
|
|
use crate::iter::{self, FromIterator, FusedIterator, TrustedLen};
|
|
use crate::marker::Destruct;
|
|
use crate::panicking::{panic, panic_str};
|
|
use crate::pin::Pin;
|
|
use crate::{
|
|
cmp, convert, hint, mem,
|
|
ops::{self, ControlFlow, Deref, DerefMut},
|
|
};
|
|
|
|
/// The `Option` type. See [the module level documentation](self) for more.
|
|
#[derive(Copy, PartialOrd, Eq, Ord, Debug, Hash)]
|
|
#[rustc_diagnostic_item = "Option"]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub enum Option<T> {
|
|
/// No value.
|
|
#[lang = "None"]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
None,
|
|
/// Some value of type `T`.
|
|
#[lang = "Some"]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
Some(#[stable(feature = "rust1", since = "1.0.0")] T),
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Type implementation
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
impl<T> Option<T> {
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Querying the contained values
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Returns `true` if the option is a [`Some`] value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x: Option<u32> = Some(2);
|
|
/// assert_eq!(x.is_some(), true);
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// assert_eq!(x.is_some(), false);
|
|
/// ```
|
|
#[must_use = "if you intended to assert that this has a value, consider `.unwrap()` instead"]
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")]
|
|
pub const fn is_some(&self) -> bool {
|
|
matches!(*self, Some(_))
|
|
}
|
|
|
|
/// Returns `true` if the option is a [`Some`] and the value inside of it matches a predicate.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(is_some_and)]
|
|
///
|
|
/// let x: Option<u32> = Some(2);
|
|
/// assert_eq!(x.is_some_and(|x| x > 1), true);
|
|
///
|
|
/// let x: Option<u32> = Some(0);
|
|
/// assert_eq!(x.is_some_and(|x| x > 1), false);
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// assert_eq!(x.is_some_and(|x| x > 1), false);
|
|
/// ```
|
|
#[must_use]
|
|
#[inline]
|
|
#[unstable(feature = "is_some_and", issue = "93050")]
|
|
pub fn is_some_and(self, f: impl FnOnce(T) -> bool) -> bool {
|
|
match self {
|
|
None => false,
|
|
Some(x) => f(x),
|
|
}
|
|
}
|
|
|
|
/// Returns `true` if the option is a [`None`] value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x: Option<u32> = Some(2);
|
|
/// assert_eq!(x.is_none(), false);
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// assert_eq!(x.is_none(), true);
|
|
/// ```
|
|
#[must_use = "if you intended to assert that this doesn't have a value, consider \
|
|
`.and_then(|_| panic!(\"`Option` had a value when expected `None`\"))` instead"]
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")]
|
|
pub const fn is_none(&self) -> bool {
|
|
!self.is_some()
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Adapter for working with references
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Converts from `&Option<T>` to `Option<&T>`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Calculates the length of an <code>Option<[String]></code> as an <code>Option<[usize]></code>
|
|
/// without moving the [`String`]. The [`map`] method takes the `self` argument by value,
|
|
/// consuming the original, so this technique uses `as_ref` to first take an `Option` to a
|
|
/// reference to the value inside the original.
|
|
///
|
|
/// [`map`]: Option::map
|
|
/// [String]: ../../std/string/struct.String.html "String"
|
|
/// [`String`]: ../../std/string/struct.String.html "String"
|
|
///
|
|
/// ```
|
|
/// let text: Option<String> = Some("Hello, world!".to_string());
|
|
/// // First, cast `Option<String>` to `Option<&String>` with `as_ref`,
|
|
/// // then consume *that* with `map`, leaving `text` on the stack.
|
|
/// let text_length: Option<usize> = text.as_ref().map(|s| s.len());
|
|
/// println!("still can print text: {text:?}");
|
|
/// ```
|
|
#[inline]
|
|
#[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub const fn as_ref(&self) -> Option<&T> {
|
|
match *self {
|
|
Some(ref x) => Some(x),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Converts from `&mut Option<T>` to `Option<&mut T>`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = Some(2);
|
|
/// match x.as_mut() {
|
|
/// Some(v) => *v = 42,
|
|
/// None => {},
|
|
/// }
|
|
/// assert_eq!(x, Some(42));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn as_mut(&mut self) -> Option<&mut T> {
|
|
match *self {
|
|
Some(ref mut x) => Some(x),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Converts from <code>[Pin]<[&]Option\<T>></code> to <code>Option<[Pin]<[&]T>></code>.
|
|
///
|
|
/// [&]: reference "shared reference"
|
|
#[inline]
|
|
#[must_use]
|
|
#[stable(feature = "pin", since = "1.33.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn as_pin_ref(self: Pin<&Self>) -> Option<Pin<&T>> {
|
|
match Pin::get_ref(self).as_ref() {
|
|
// SAFETY: `x` is guaranteed to be pinned because it comes from `self`
|
|
// which is pinned.
|
|
Some(x) => unsafe { Some(Pin::new_unchecked(x)) },
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Converts from <code>[Pin]<[&mut] Option\<T>></code> to <code>Option<[Pin]<[&mut] T>></code>.
|
|
///
|
|
/// [&mut]: reference "mutable reference"
|
|
#[inline]
|
|
#[must_use]
|
|
#[stable(feature = "pin", since = "1.33.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn as_pin_mut(self: Pin<&mut Self>) -> Option<Pin<&mut T>> {
|
|
// SAFETY: `get_unchecked_mut` is never used to move the `Option` inside `self`.
|
|
// `x` is guaranteed to be pinned because it comes from `self` which is pinned.
|
|
unsafe {
|
|
match Pin::get_unchecked_mut(self).as_mut() {
|
|
Some(x) => Some(Pin::new_unchecked(x)),
|
|
None => None,
|
|
}
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Getting to contained values
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Returns the contained [`Some`] value, consuming the `self` value.
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is a [`None`] with a custom panic message provided by
|
|
/// `msg`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some("value");
|
|
/// assert_eq!(x.expect("fruits are healthy"), "value");
|
|
/// ```
|
|
///
|
|
/// ```should_panic
|
|
/// let x: Option<&str> = None;
|
|
/// x.expect("fruits are healthy"); // panics with `fruits are healthy`
|
|
/// ```
|
|
///
|
|
/// # Recommended Message Style
|
|
///
|
|
/// We recommend that `expect` messages are used to describe the reason you
|
|
/// _expect_ the `Option` should be `Some`.
|
|
///
|
|
/// ```should_panic
|
|
/// # let slice: &[u8] = &[];
|
|
/// let item = slice.get(0)
|
|
/// .expect("slice should not be empty");
|
|
/// ```
|
|
///
|
|
/// **Hint**: If you're having trouble remembering how to phrase expect
|
|
/// error messages remember to focus on the word "should" as in "env
|
|
/// variable should be set by blah" or "the given binary should be available
|
|
/// and executable by the current user".
|
|
///
|
|
/// For more detail on expect message styles and the reasoning behind our
|
|
/// recommendation please refer to the section on ["Common Message
|
|
/// Styles"](../../std/error/index.html#common-message-styles) in the [`std::error`](../../std/error/index.html) module docs.
|
|
#[inline]
|
|
#[track_caller]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn expect(self, msg: &str) -> T {
|
|
match self {
|
|
Some(val) => val,
|
|
None => expect_failed(msg),
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Some`] value, consuming the `self` value.
|
|
///
|
|
/// Because this function may panic, its use is generally discouraged.
|
|
/// Instead, prefer to use pattern matching and handle the [`None`]
|
|
/// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
|
|
/// [`unwrap_or_default`].
|
|
///
|
|
/// [`unwrap_or`]: Option::unwrap_or
|
|
/// [`unwrap_or_else`]: Option::unwrap_or_else
|
|
/// [`unwrap_or_default`]: Option::unwrap_or_default
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the self value equals [`None`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some("air");
|
|
/// assert_eq!(x.unwrap(), "air");
|
|
/// ```
|
|
///
|
|
/// ```should_panic
|
|
/// let x: Option<&str> = None;
|
|
/// assert_eq!(x.unwrap(), "air"); // fails
|
|
/// ```
|
|
#[inline]
|
|
#[track_caller]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn unwrap(self) -> T {
|
|
match self {
|
|
Some(val) => val,
|
|
None => panic("called `Option::unwrap()` on a `None` value"),
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Some`] value or a provided default.
|
|
///
|
|
/// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing
|
|
/// the result of a function call, it is recommended to use [`unwrap_or_else`],
|
|
/// which is lazily evaluated.
|
|
///
|
|
/// [`unwrap_or_else`]: Option::unwrap_or_else
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// assert_eq!(Some("car").unwrap_or("bike"), "car");
|
|
/// assert_eq!(None.unwrap_or("bike"), "bike");
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn unwrap_or(self, default: T) -> T
|
|
where
|
|
T: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(x) => x,
|
|
None => default,
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Some`] value or computes it from a closure.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let k = 10;
|
|
/// assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4);
|
|
/// assert_eq!(None.unwrap_or_else(|| 2 * k), 20);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn unwrap_or_else<F>(self, f: F) -> T
|
|
where
|
|
F: ~const FnOnce() -> T,
|
|
F: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(x) => x,
|
|
None => f(),
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Some`] value or a default.
|
|
///
|
|
/// Consumes the `self` argument then, if [`Some`], returns the contained
|
|
/// value, otherwise if [`None`], returns the [default value] for that
|
|
/// type.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x: Option<u32> = None;
|
|
/// let y: Option<u32> = Some(12);
|
|
///
|
|
/// assert_eq!(x.unwrap_or_default(), 0);
|
|
/// assert_eq!(y.unwrap_or_default(), 12);
|
|
/// ```
|
|
///
|
|
/// [default value]: Default::default
|
|
/// [`parse`]: str::parse
|
|
/// [`FromStr`]: crate::str::FromStr
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn unwrap_or_default(self) -> T
|
|
where
|
|
T: ~const Default,
|
|
{
|
|
match self {
|
|
Some(x) => x,
|
|
None => Default::default(),
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Some`] value, consuming the `self` value,
|
|
/// without checking that the value is not [`None`].
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// Calling this method on [`None`] is *[undefined behavior]*.
|
|
///
|
|
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some("air");
|
|
/// assert_eq!(unsafe { x.unwrap_unchecked() }, "air");
|
|
/// ```
|
|
///
|
|
/// ```no_run
|
|
/// let x: Option<&str> = None;
|
|
/// assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior!
|
|
/// ```
|
|
#[inline]
|
|
#[track_caller]
|
|
#[stable(feature = "option_result_unwrap_unchecked", since = "1.58.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const unsafe fn unwrap_unchecked(self) -> T {
|
|
debug_assert!(self.is_some());
|
|
match self {
|
|
Some(val) => val,
|
|
// SAFETY: the safety contract must be upheld by the caller.
|
|
None => unsafe { hint::unreachable_unchecked() },
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Transforming contained values
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value (if `Some`) or returns `None` (if `None`).
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Calculates the length of an <code>Option<[String]></code> as an
|
|
/// <code>Option<[usize]></code>, consuming the original:
|
|
///
|
|
/// [String]: ../../std/string/struct.String.html "String"
|
|
/// ```
|
|
/// let maybe_some_string = Some(String::from("Hello, World!"));
|
|
/// // `Option::map` takes self *by value*, consuming `maybe_some_string`
|
|
/// let maybe_some_len = maybe_some_string.map(|s| s.len());
|
|
/// assert_eq!(maybe_some_len, Some(13));
|
|
///
|
|
/// let x: Option<&str> = None;
|
|
/// assert_eq!(x.map(|s| s.len()), None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn map<U, F>(self, f: F) -> Option<U>
|
|
where
|
|
F: ~const FnOnce(T) -> U,
|
|
F: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(x) => Some(f(x)),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Calls the provided closure with a reference to the contained value (if [`Some`]).
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(result_option_inspect)]
|
|
///
|
|
/// let v = vec![1, 2, 3, 4, 5];
|
|
///
|
|
/// // prints "got: 4"
|
|
/// let x: Option<&usize> = v.get(3).inspect(|x| println!("got: {x}"));
|
|
///
|
|
/// // prints nothing
|
|
/// let x: Option<&usize> = v.get(5).inspect(|x| println!("got: {x}"));
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "result_option_inspect", issue = "91345")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn inspect<F>(self, f: F) -> Self
|
|
where
|
|
F: ~const FnOnce(&T),
|
|
F: ~const Destruct,
|
|
{
|
|
if let Some(ref x) = self {
|
|
f(x);
|
|
}
|
|
|
|
self
|
|
}
|
|
|
|
/// Returns the provided default result (if none),
|
|
/// or applies a function to the contained value (if any).
|
|
///
|
|
/// Arguments passed to `map_or` are eagerly evaluated; if you are passing
|
|
/// the result of a function call, it is recommended to use [`map_or_else`],
|
|
/// which is lazily evaluated.
|
|
///
|
|
/// [`map_or_else`]: Option::map_or_else
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some("foo");
|
|
/// assert_eq!(x.map_or(42, |v| v.len()), 3);
|
|
///
|
|
/// let x: Option<&str> = None;
|
|
/// assert_eq!(x.map_or(42, |v| v.len()), 42);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn map_or<U, F>(self, default: U, f: F) -> U
|
|
where
|
|
F: ~const FnOnce(T) -> U,
|
|
F: ~const Destruct,
|
|
U: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(t) => f(t),
|
|
None => default,
|
|
}
|
|
}
|
|
|
|
/// Computes a default function result (if none), or
|
|
/// applies a different function to the contained value (if any).
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let k = 21;
|
|
///
|
|
/// let x = Some("foo");
|
|
/// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3);
|
|
///
|
|
/// let x: Option<&str> = None;
|
|
/// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn map_or_else<U, D, F>(self, default: D, f: F) -> U
|
|
where
|
|
D: ~const FnOnce() -> U,
|
|
D: ~const Destruct,
|
|
F: ~const FnOnce(T) -> U,
|
|
F: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(t) => f(t),
|
|
None => default(),
|
|
}
|
|
}
|
|
|
|
/// Transforms the `Option<T>` into a [`Result<T, E>`], mapping [`Some(v)`] to
|
|
/// [`Ok(v)`] and [`None`] to [`Err(err)`].
|
|
///
|
|
/// Arguments passed to `ok_or` are eagerly evaluated; if you are passing the
|
|
/// result of a function call, it is recommended to use [`ok_or_else`], which is
|
|
/// lazily evaluated.
|
|
///
|
|
/// [`Ok(v)`]: Ok
|
|
/// [`Err(err)`]: Err
|
|
/// [`Some(v)`]: Some
|
|
/// [`ok_or_else`]: Option::ok_or_else
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some("foo");
|
|
/// assert_eq!(x.ok_or(0), Ok("foo"));
|
|
///
|
|
/// let x: Option<&str> = None;
|
|
/// assert_eq!(x.ok_or(0), Err(0));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn ok_or<E>(self, err: E) -> Result<T, E>
|
|
where
|
|
E: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(v) => Ok(v),
|
|
None => Err(err),
|
|
}
|
|
}
|
|
|
|
/// Transforms the `Option<T>` into a [`Result<T, E>`], mapping [`Some(v)`] to
|
|
/// [`Ok(v)`] and [`None`] to [`Err(err())`].
|
|
///
|
|
/// [`Ok(v)`]: Ok
|
|
/// [`Err(err())`]: Err
|
|
/// [`Some(v)`]: Some
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some("foo");
|
|
/// assert_eq!(x.ok_or_else(|| 0), Ok("foo"));
|
|
///
|
|
/// let x: Option<&str> = None;
|
|
/// assert_eq!(x.ok_or_else(|| 0), Err(0));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn ok_or_else<E, F>(self, err: F) -> Result<T, E>
|
|
where
|
|
F: ~const FnOnce() -> E,
|
|
F: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(v) => Ok(v),
|
|
None => Err(err()),
|
|
}
|
|
}
|
|
|
|
/// Converts from `Option<T>` (or `&Option<T>`) to `Option<&T::Target>`.
|
|
///
|
|
/// Leaves the original Option in-place, creating a new one with a reference
|
|
/// to the original one, additionally coercing the contents via [`Deref`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x: Option<String> = Some("hey".to_owned());
|
|
/// assert_eq!(x.as_deref(), Some("hey"));
|
|
///
|
|
/// let x: Option<String> = None;
|
|
/// assert_eq!(x.as_deref(), None);
|
|
/// ```
|
|
#[stable(feature = "option_deref", since = "1.40.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn as_deref(&self) -> Option<&T::Target>
|
|
where
|
|
T: ~const Deref,
|
|
{
|
|
match self.as_ref() {
|
|
Some(t) => Some(t.deref()),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Converts from `Option<T>` (or `&mut Option<T>`) to `Option<&mut T::Target>`.
|
|
///
|
|
/// Leaves the original `Option` in-place, creating a new one containing a mutable reference to
|
|
/// the inner type's [`Deref::Target`] type.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x: Option<String> = Some("hey".to_owned());
|
|
/// assert_eq!(x.as_deref_mut().map(|x| {
|
|
/// x.make_ascii_uppercase();
|
|
/// x
|
|
/// }), Some("HEY".to_owned().as_mut_str()));
|
|
/// ```
|
|
#[stable(feature = "option_deref", since = "1.40.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn as_deref_mut(&mut self) -> Option<&mut T::Target>
|
|
where
|
|
T: ~const DerefMut,
|
|
{
|
|
match self.as_mut() {
|
|
Some(t) => Some(t.deref_mut()),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Iterator constructors
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Returns an iterator over the possibly contained value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some(4);
|
|
/// assert_eq!(x.iter().next(), Some(&4));
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// assert_eq!(x.iter().next(), None);
|
|
/// ```
|
|
#[inline]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub const fn iter(&self) -> Iter<'_, T> {
|
|
Iter { inner: Item { opt: self.as_ref() } }
|
|
}
|
|
|
|
/// Returns a mutable iterator over the possibly contained value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = Some(4);
|
|
/// match x.iter_mut().next() {
|
|
/// Some(v) => *v = 42,
|
|
/// None => {},
|
|
/// }
|
|
/// assert_eq!(x, Some(42));
|
|
///
|
|
/// let mut x: Option<u32> = None;
|
|
/// assert_eq!(x.iter_mut().next(), None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub fn iter_mut(&mut self) -> IterMut<'_, T> {
|
|
IterMut { inner: Item { opt: self.as_mut() } }
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Boolean operations on the values, eager and lazy
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Returns [`None`] if the option is [`None`], otherwise returns `optb`.
|
|
///
|
|
/// Arguments passed to `and` are eagerly evaluated; if you are passing the
|
|
/// result of a function call, it is recommended to use [`and_then`], which is
|
|
/// lazily evaluated.
|
|
///
|
|
/// [`and_then`]: Option::and_then
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some(2);
|
|
/// let y: Option<&str> = None;
|
|
/// assert_eq!(x.and(y), None);
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// let y = Some("foo");
|
|
/// assert_eq!(x.and(y), None);
|
|
///
|
|
/// let x = Some(2);
|
|
/// let y = Some("foo");
|
|
/// assert_eq!(x.and(y), Some("foo"));
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// let y: Option<&str> = None;
|
|
/// assert_eq!(x.and(y), None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn and<U>(self, optb: Option<U>) -> Option<U>
|
|
where
|
|
T: ~const Destruct,
|
|
U: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(_) => optb,
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Returns [`None`] if the option is [`None`], otherwise calls `f` with the
|
|
/// wrapped value and returns the result.
|
|
///
|
|
/// Some languages call this operation flatmap.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// fn sq_then_to_string(x: u32) -> Option<String> {
|
|
/// x.checked_mul(x).map(|sq| sq.to_string())
|
|
/// }
|
|
///
|
|
/// assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string()));
|
|
/// assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None); // overflowed!
|
|
/// assert_eq!(None.and_then(sq_then_to_string), None);
|
|
/// ```
|
|
///
|
|
/// Often used to chain fallible operations that may return [`None`].
|
|
///
|
|
/// ```
|
|
/// let arr_2d = [["A0", "A1"], ["B0", "B1"]];
|
|
///
|
|
/// let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1));
|
|
/// assert_eq!(item_0_1, Some(&"A1"));
|
|
///
|
|
/// let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0));
|
|
/// assert_eq!(item_2_0, None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn and_then<U, F>(self, f: F) -> Option<U>
|
|
where
|
|
F: ~const FnOnce(T) -> Option<U>,
|
|
F: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(x) => f(x),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Returns [`None`] if the option is [`None`], otherwise calls `predicate`
|
|
/// with the wrapped value and returns:
|
|
///
|
|
/// - [`Some(t)`] if `predicate` returns `true` (where `t` is the wrapped
|
|
/// value), and
|
|
/// - [`None`] if `predicate` returns `false`.
|
|
///
|
|
/// This function works similar to [`Iterator::filter()`]. You can imagine
|
|
/// the `Option<T>` being an iterator over one or zero elements. `filter()`
|
|
/// lets you decide which elements to keep.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```rust
|
|
/// fn is_even(n: &i32) -> bool {
|
|
/// n % 2 == 0
|
|
/// }
|
|
///
|
|
/// assert_eq!(None.filter(is_even), None);
|
|
/// assert_eq!(Some(3).filter(is_even), None);
|
|
/// assert_eq!(Some(4).filter(is_even), Some(4));
|
|
/// ```
|
|
///
|
|
/// [`Some(t)`]: Some
|
|
#[inline]
|
|
#[stable(feature = "option_filter", since = "1.27.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn filter<P>(self, predicate: P) -> Self
|
|
where
|
|
T: ~const Destruct,
|
|
P: ~const FnOnce(&T) -> bool,
|
|
P: ~const Destruct,
|
|
{
|
|
if let Some(x) = self {
|
|
if predicate(&x) {
|
|
return Some(x);
|
|
}
|
|
}
|
|
None
|
|
}
|
|
|
|
/// Returns the option if it contains a value, otherwise returns `optb`.
|
|
///
|
|
/// Arguments passed to `or` are eagerly evaluated; if you are passing the
|
|
/// result of a function call, it is recommended to use [`or_else`], which is
|
|
/// lazily evaluated.
|
|
///
|
|
/// [`or_else`]: Option::or_else
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some(2);
|
|
/// let y = None;
|
|
/// assert_eq!(x.or(y), Some(2));
|
|
///
|
|
/// let x = None;
|
|
/// let y = Some(100);
|
|
/// assert_eq!(x.or(y), Some(100));
|
|
///
|
|
/// let x = Some(2);
|
|
/// let y = Some(100);
|
|
/// assert_eq!(x.or(y), Some(2));
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// let y = None;
|
|
/// assert_eq!(x.or(y), None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn or(self, optb: Option<T>) -> Option<T>
|
|
where
|
|
T: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(x) => Some(x),
|
|
None => optb,
|
|
}
|
|
}
|
|
|
|
/// Returns the option if it contains a value, otherwise calls `f` and
|
|
/// returns the result.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// fn nobody() -> Option<&'static str> { None }
|
|
/// fn vikings() -> Option<&'static str> { Some("vikings") }
|
|
///
|
|
/// assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians"));
|
|
/// assert_eq!(None.or_else(vikings), Some("vikings"));
|
|
/// assert_eq!(None.or_else(nobody), None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn or_else<F>(self, f: F) -> Option<T>
|
|
where
|
|
F: ~const FnOnce() -> Option<T>,
|
|
F: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some(x) => Some(x),
|
|
None => f(),
|
|
}
|
|
}
|
|
|
|
/// Returns [`Some`] if exactly one of `self`, `optb` is [`Some`], otherwise returns [`None`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some(2);
|
|
/// let y: Option<u32> = None;
|
|
/// assert_eq!(x.xor(y), Some(2));
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// let y = Some(2);
|
|
/// assert_eq!(x.xor(y), Some(2));
|
|
///
|
|
/// let x = Some(2);
|
|
/// let y = Some(2);
|
|
/// assert_eq!(x.xor(y), None);
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// let y: Option<u32> = None;
|
|
/// assert_eq!(x.xor(y), None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "option_xor", since = "1.37.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn xor(self, optb: Option<T>) -> Option<T>
|
|
where
|
|
T: ~const Destruct,
|
|
{
|
|
match (self, optb) {
|
|
(Some(a), None) => Some(a),
|
|
(None, Some(b)) => Some(b),
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Entry-like operations to insert a value and return a reference
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Inserts `value` into the option, then returns a mutable reference to it.
|
|
///
|
|
/// If the option already contains a value, the old value is dropped.
|
|
///
|
|
/// See also [`Option::get_or_insert`], which doesn't update the value if
|
|
/// the option already contains [`Some`].
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// let mut opt = None;
|
|
/// let val = opt.insert(1);
|
|
/// assert_eq!(*val, 1);
|
|
/// assert_eq!(opt.unwrap(), 1);
|
|
/// let val = opt.insert(2);
|
|
/// assert_eq!(*val, 2);
|
|
/// *val = 3;
|
|
/// assert_eq!(opt.unwrap(), 3);
|
|
/// ```
|
|
#[must_use = "if you intended to set a value, consider assignment instead"]
|
|
#[inline]
|
|
#[stable(feature = "option_insert", since = "1.53.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn insert(&mut self, value: T) -> &mut T
|
|
where
|
|
T: ~const Destruct,
|
|
{
|
|
*self = Some(value);
|
|
|
|
// SAFETY: the code above just filled the option
|
|
unsafe { self.as_mut().unwrap_unchecked() }
|
|
}
|
|
|
|
/// Inserts `value` into the option if it is [`None`], then
|
|
/// returns a mutable reference to the contained value.
|
|
///
|
|
/// See also [`Option::insert`], which updates the value even if
|
|
/// the option already contains [`Some`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = None;
|
|
///
|
|
/// {
|
|
/// let y: &mut u32 = x.get_or_insert(5);
|
|
/// assert_eq!(y, &5);
|
|
///
|
|
/// *y = 7;
|
|
/// }
|
|
///
|
|
/// assert_eq!(x, Some(7));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "option_entry", since = "1.20.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn get_or_insert(&mut self, value: T) -> &mut T
|
|
where
|
|
T: ~const Destruct,
|
|
{
|
|
if let None = *self {
|
|
*self = Some(value);
|
|
}
|
|
|
|
// SAFETY: a `None` variant for `self` would have been replaced by a `Some`
|
|
// variant in the code above.
|
|
unsafe { self.as_mut().unwrap_unchecked() }
|
|
}
|
|
|
|
/// Inserts the default value into the option if it is [`None`], then
|
|
/// returns a mutable reference to the contained value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(option_get_or_insert_default)]
|
|
///
|
|
/// let mut x = None;
|
|
///
|
|
/// {
|
|
/// let y: &mut u32 = x.get_or_insert_default();
|
|
/// assert_eq!(y, &0);
|
|
///
|
|
/// *y = 7;
|
|
/// }
|
|
///
|
|
/// assert_eq!(x, Some(7));
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "option_get_or_insert_default", issue = "82901")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn get_or_insert_default(&mut self) -> &mut T
|
|
where
|
|
T: ~const Default,
|
|
{
|
|
const fn default<T: ~const Default>() -> T {
|
|
T::default()
|
|
}
|
|
|
|
self.get_or_insert_with(default)
|
|
}
|
|
|
|
/// Inserts a value computed from `f` into the option if it is [`None`],
|
|
/// then returns a mutable reference to the contained value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = None;
|
|
///
|
|
/// {
|
|
/// let y: &mut u32 = x.get_or_insert_with(|| 5);
|
|
/// assert_eq!(y, &5);
|
|
///
|
|
/// *y = 7;
|
|
/// }
|
|
///
|
|
/// assert_eq!(x, Some(7));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "option_entry", since = "1.20.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn get_or_insert_with<F>(&mut self, f: F) -> &mut T
|
|
where
|
|
F: ~const FnOnce() -> T,
|
|
F: ~const Destruct,
|
|
{
|
|
if let None = *self {
|
|
// the compiler isn't smart enough to know that we are not dropping a `T`
|
|
// here and wants us to ensure `T` can be dropped at compile time.
|
|
mem::forget(mem::replace(self, Some(f())))
|
|
}
|
|
|
|
// SAFETY: a `None` variant for `self` would have been replaced by a `Some`
|
|
// variant in the code above.
|
|
unsafe { self.as_mut().unwrap_unchecked() }
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Misc
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Takes the value out of the option, leaving a [`None`] in its place.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = Some(2);
|
|
/// let y = x.take();
|
|
/// assert_eq!(x, None);
|
|
/// assert_eq!(y, Some(2));
|
|
///
|
|
/// let mut x: Option<u32> = None;
|
|
/// let y = x.take();
|
|
/// assert_eq!(x, None);
|
|
/// assert_eq!(y, None);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn take(&mut self) -> Option<T> {
|
|
// FIXME replace `mem::replace` by `mem::take` when the latter is const ready
|
|
mem::replace(self, None)
|
|
}
|
|
|
|
/// Replaces the actual value in the option by the value given in parameter,
|
|
/// returning the old value if present,
|
|
/// leaving a [`Some`] in its place without deinitializing either one.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = Some(2);
|
|
/// let old = x.replace(5);
|
|
/// assert_eq!(x, Some(5));
|
|
/// assert_eq!(old, Some(2));
|
|
///
|
|
/// let mut x = None;
|
|
/// let old = x.replace(3);
|
|
/// assert_eq!(x, Some(3));
|
|
/// assert_eq!(old, None);
|
|
/// ```
|
|
#[inline]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
#[stable(feature = "option_replace", since = "1.31.0")]
|
|
pub const fn replace(&mut self, value: T) -> Option<T> {
|
|
mem::replace(self, Some(value))
|
|
}
|
|
|
|
/// Returns `true` if the option is a [`Some`] value containing the given value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(option_result_contains)]
|
|
///
|
|
/// let x: Option<u32> = Some(2);
|
|
/// assert_eq!(x.contains(&2), true);
|
|
///
|
|
/// let x: Option<u32> = Some(3);
|
|
/// assert_eq!(x.contains(&2), false);
|
|
///
|
|
/// let x: Option<u32> = None;
|
|
/// assert_eq!(x.contains(&2), false);
|
|
/// ```
|
|
#[must_use]
|
|
#[inline]
|
|
#[unstable(feature = "option_result_contains", issue = "62358")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn contains<U>(&self, x: &U) -> bool
|
|
where
|
|
U: ~const PartialEq<T>,
|
|
{
|
|
match self {
|
|
Some(y) => x.eq(y),
|
|
None => false,
|
|
}
|
|
}
|
|
|
|
/// Zips `self` with another `Option`.
|
|
///
|
|
/// If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some((s, o))`.
|
|
/// Otherwise, `None` is returned.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some(1);
|
|
/// let y = Some("hi");
|
|
/// let z = None::<u8>;
|
|
///
|
|
/// assert_eq!(x.zip(y), Some((1, "hi")));
|
|
/// assert_eq!(x.zip(z), None);
|
|
/// ```
|
|
#[stable(feature = "option_zip_option", since = "1.46.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn zip<U>(self, other: Option<U>) -> Option<(T, U)>
|
|
where
|
|
T: ~const Destruct,
|
|
U: ~const Destruct,
|
|
{
|
|
match (self, other) {
|
|
(Some(a), Some(b)) => Some((a, b)),
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
/// Zips `self` and another `Option` with function `f`.
|
|
///
|
|
/// If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some(f(s, o))`.
|
|
/// Otherwise, `None` is returned.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(option_zip)]
|
|
///
|
|
/// #[derive(Debug, PartialEq)]
|
|
/// struct Point {
|
|
/// x: f64,
|
|
/// y: f64,
|
|
/// }
|
|
///
|
|
/// impl Point {
|
|
/// fn new(x: f64, y: f64) -> Self {
|
|
/// Self { x, y }
|
|
/// }
|
|
/// }
|
|
///
|
|
/// let x = Some(17.5);
|
|
/// let y = Some(42.7);
|
|
///
|
|
/// assert_eq!(x.zip_with(y, Point::new), Some(Point { x: 17.5, y: 42.7 }));
|
|
/// assert_eq!(x.zip_with(None, Point::new), None);
|
|
/// ```
|
|
#[unstable(feature = "option_zip", issue = "70086")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>
|
|
where
|
|
F: ~const FnOnce(T, U) -> R,
|
|
F: ~const Destruct,
|
|
T: ~const Destruct,
|
|
U: ~const Destruct,
|
|
{
|
|
match (self, other) {
|
|
(Some(a), Some(b)) => Some(f(a, b)),
|
|
_ => None,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T, U> Option<(T, U)> {
|
|
/// Unzips an option containing a tuple of two options.
|
|
///
|
|
/// If `self` is `Some((a, b))` this method returns `(Some(a), Some(b))`.
|
|
/// Otherwise, `(None, None)` is returned.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some((1, "hi"));
|
|
/// let y = None::<(u8, u32)>;
|
|
///
|
|
/// assert_eq!(x.unzip(), (Some(1), Some("hi")));
|
|
/// assert_eq!(y.unzip(), (None, None));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "unzip_option", since = "1.66.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn unzip(self) -> (Option<T>, Option<U>)
|
|
where
|
|
T: ~const Destruct,
|
|
U: ~const Destruct,
|
|
{
|
|
match self {
|
|
Some((a, b)) => (Some(a), Some(b)),
|
|
None => (None, None),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T> Option<&T> {
|
|
/// Maps an `Option<&T>` to an `Option<T>` by copying the contents of the
|
|
/// option.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = 12;
|
|
/// let opt_x = Some(&x);
|
|
/// assert_eq!(opt_x, Some(&12));
|
|
/// let copied = opt_x.copied();
|
|
/// assert_eq!(copied, Some(12));
|
|
/// ```
|
|
#[must_use = "`self` will be dropped if the result is not used"]
|
|
#[stable(feature = "copied", since = "1.35.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn copied(self) -> Option<T>
|
|
where
|
|
T: Copy,
|
|
{
|
|
// FIXME: this implementation, which sidesteps using `Option::map` since it's not const
|
|
// ready yet, should be reverted when possible to avoid code repetition
|
|
match self {
|
|
Some(&v) => Some(v),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the
|
|
/// option.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = 12;
|
|
/// let opt_x = Some(&x);
|
|
/// assert_eq!(opt_x, Some(&12));
|
|
/// let cloned = opt_x.cloned();
|
|
/// assert_eq!(cloned, Some(12));
|
|
/// ```
|
|
#[must_use = "`self` will be dropped if the result is not used"]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_option_cloned", issue = "91582")]
|
|
pub const fn cloned(self) -> Option<T>
|
|
where
|
|
T: ~const Clone,
|
|
{
|
|
match self {
|
|
Some(t) => Some(t.clone()),
|
|
None => None,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T> Option<&mut T> {
|
|
/// Maps an `Option<&mut T>` to an `Option<T>` by copying the contents of the
|
|
/// option.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = 12;
|
|
/// let opt_x = Some(&mut x);
|
|
/// assert_eq!(opt_x, Some(&mut 12));
|
|
/// let copied = opt_x.copied();
|
|
/// assert_eq!(copied, Some(12));
|
|
/// ```
|
|
#[must_use = "`self` will be dropped if the result is not used"]
|
|
#[stable(feature = "copied", since = "1.35.0")]
|
|
#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
|
|
pub const fn copied(self) -> Option<T>
|
|
where
|
|
T: Copy,
|
|
{
|
|
match self {
|
|
Some(&mut t) => Some(t),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
/// Maps an `Option<&mut T>` to an `Option<T>` by cloning the contents of the
|
|
/// option.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut x = 12;
|
|
/// let opt_x = Some(&mut x);
|
|
/// assert_eq!(opt_x, Some(&mut 12));
|
|
/// let cloned = opt_x.cloned();
|
|
/// assert_eq!(cloned, Some(12));
|
|
/// ```
|
|
#[must_use = "`self` will be dropped if the result is not used"]
|
|
#[stable(since = "1.26.0", feature = "option_ref_mut_cloned")]
|
|
#[rustc_const_unstable(feature = "const_option_cloned", issue = "91582")]
|
|
pub const fn cloned(self) -> Option<T>
|
|
where
|
|
T: ~const Clone,
|
|
{
|
|
match self {
|
|
Some(t) => Some(t.clone()),
|
|
None => None,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T, E> Option<Result<T, E>> {
|
|
/// Transposes an `Option` of a [`Result`] into a [`Result`] of an `Option`.
|
|
///
|
|
/// [`None`] will be mapped to <code>[Ok]\([None])</code>.
|
|
/// <code>[Some]\([Ok]\(\_))</code> and <code>[Some]\([Err]\(\_))</code> will be mapped to
|
|
/// <code>[Ok]\([Some]\(\_))</code> and <code>[Err]\(\_)</code>.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #[derive(Debug, Eq, PartialEq)]
|
|
/// struct SomeErr;
|
|
///
|
|
/// let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
|
|
/// let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
|
|
/// assert_eq!(x, y.transpose());
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "transpose_result", since = "1.33.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn transpose(self) -> Result<Option<T>, E> {
|
|
match self {
|
|
Some(Ok(x)) => Ok(Some(x)),
|
|
Some(Err(e)) => Err(e),
|
|
None => Ok(None),
|
|
}
|
|
}
|
|
}
|
|
|
|
// This is a separate function to reduce the code size of .expect() itself.
|
|
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
|
|
#[cfg_attr(feature = "panic_immediate_abort", inline)]
|
|
#[cold]
|
|
#[track_caller]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
const fn expect_failed(msg: &str) -> ! {
|
|
panic_str(msg)
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Trait implementations
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
|
|
impl<T> const Clone for Option<T>
|
|
where
|
|
T: ~const Clone + ~const Destruct,
|
|
{
|
|
#[inline]
|
|
fn clone(&self) -> Self {
|
|
match self {
|
|
Some(x) => Some(x.clone()),
|
|
None => None,
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn clone_from(&mut self, source: &Self) {
|
|
match (self, source) {
|
|
(Some(to), Some(from)) => to.clone_from(from),
|
|
(to, from) => *to = from.clone(),
|
|
}
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
|
|
impl<T> const Default for Option<T> {
|
|
/// Returns [`None`][Option::None].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let opt: Option<u32> = Option::default();
|
|
/// assert!(opt.is_none());
|
|
/// ```
|
|
#[inline]
|
|
fn default() -> Option<T> {
|
|
None
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T> IntoIterator for Option<T> {
|
|
type Item = T;
|
|
type IntoIter = IntoIter<T>;
|
|
|
|
/// Returns a consuming iterator over the possibly contained value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x = Some("string");
|
|
/// let v: Vec<&str> = x.into_iter().collect();
|
|
/// assert_eq!(v, ["string"]);
|
|
///
|
|
/// let x = None;
|
|
/// let v: Vec<&str> = x.into_iter().collect();
|
|
/// assert!(v.is_empty());
|
|
/// ```
|
|
#[inline]
|
|
fn into_iter(self) -> IntoIter<T> {
|
|
IntoIter { inner: Item { opt: self } }
|
|
}
|
|
}
|
|
|
|
#[stable(since = "1.4.0", feature = "option_iter")]
|
|
impl<'a, T> IntoIterator for &'a Option<T> {
|
|
type Item = &'a T;
|
|
type IntoIter = Iter<'a, T>;
|
|
|
|
fn into_iter(self) -> Iter<'a, T> {
|
|
self.iter()
|
|
}
|
|
}
|
|
|
|
#[stable(since = "1.4.0", feature = "option_iter")]
|
|
impl<'a, T> IntoIterator for &'a mut Option<T> {
|
|
type Item = &'a mut T;
|
|
type IntoIter = IterMut<'a, T>;
|
|
|
|
fn into_iter(self) -> IterMut<'a, T> {
|
|
self.iter_mut()
|
|
}
|
|
}
|
|
|
|
#[stable(since = "1.12.0", feature = "option_from")]
|
|
#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
|
|
impl<T> const From<T> for Option<T> {
|
|
/// Moves `val` into a new [`Some`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let o: Option<u8> = Option::from(67);
|
|
///
|
|
/// assert_eq!(Some(67), o);
|
|
/// ```
|
|
fn from(val: T) -> Option<T> {
|
|
Some(val)
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "option_ref_from_ref_option", since = "1.30.0")]
|
|
#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
|
|
impl<'a, T> const From<&'a Option<T>> for Option<&'a T> {
|
|
/// Converts from `&Option<T>` to `Option<&T>`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Converts an <code>[Option]<[String]></code> into an <code>[Option]<[usize]></code>, preserving
|
|
/// the original. The [`map`] method takes the `self` argument by value, consuming the original,
|
|
/// so this technique uses `from` to first take an [`Option`] to a reference
|
|
/// to the value inside the original.
|
|
///
|
|
/// [`map`]: Option::map
|
|
/// [String]: ../../std/string/struct.String.html "String"
|
|
///
|
|
/// ```
|
|
/// let s: Option<String> = Some(String::from("Hello, Rustaceans!"));
|
|
/// let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len());
|
|
///
|
|
/// println!("Can still print s: {s:?}");
|
|
///
|
|
/// assert_eq!(o, Some(18));
|
|
/// ```
|
|
fn from(o: &'a Option<T>) -> Option<&'a T> {
|
|
o.as_ref()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "option_ref_from_ref_option", since = "1.30.0")]
|
|
#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
|
|
impl<'a, T> const From<&'a mut Option<T>> for Option<&'a mut T> {
|
|
/// Converts from `&mut Option<T>` to `Option<&mut T>`
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut s = Some(String::from("Hello"));
|
|
/// let o: Option<&mut String> = Option::from(&mut s);
|
|
///
|
|
/// match o {
|
|
/// Some(t) => *t = String::from("Hello, Rustaceans!"),
|
|
/// None => (),
|
|
/// }
|
|
///
|
|
/// assert_eq!(s, Some(String::from("Hello, Rustaceans!")));
|
|
/// ```
|
|
fn from(o: &'a mut Option<T>) -> Option<&'a mut T> {
|
|
o.as_mut()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T> crate::marker::StructuralPartialEq for Option<T> {}
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: PartialEq> PartialEq for Option<T> {
|
|
#[inline]
|
|
fn eq(&self, other: &Self) -> bool {
|
|
SpecOptionPartialEq::eq(self, other)
|
|
}
|
|
}
|
|
|
|
/// This specialization trait is a workaround for LLVM not currently (2023-01)
|
|
/// being able to optimize this itself, even though Alive confirms that it would
|
|
/// be legal to do so: <https://github.com/llvm/llvm-project/issues/52622>
|
|
///
|
|
/// Once that's fixed, `Option` should go back to deriving `PartialEq`, as
|
|
/// it used to do before <https://github.com/rust-lang/rust/pull/103556>.
|
|
#[unstable(feature = "spec_option_partial_eq", issue = "none", reason = "exposed only for rustc")]
|
|
#[doc(hidden)]
|
|
pub trait SpecOptionPartialEq: Sized {
|
|
fn eq(l: &Option<Self>, other: &Option<Self>) -> bool;
|
|
}
|
|
|
|
#[unstable(feature = "spec_option_partial_eq", issue = "none", reason = "exposed only for rustc")]
|
|
impl<T: PartialEq> SpecOptionPartialEq for T {
|
|
#[inline]
|
|
default fn eq(l: &Option<T>, r: &Option<T>) -> bool {
|
|
match (l, r) {
|
|
(Some(l), Some(r)) => *l == *r,
|
|
(None, None) => true,
|
|
_ => false,
|
|
}
|
|
}
|
|
}
|
|
|
|
macro_rules! non_zero_option {
|
|
( $( #[$stability: meta] $NZ:ty; )+ ) => {
|
|
$(
|
|
#[$stability]
|
|
impl SpecOptionPartialEq for $NZ {
|
|
#[inline]
|
|
fn eq(l: &Option<Self>, r: &Option<Self>) -> bool {
|
|
l.map(Self::get).unwrap_or(0) == r.map(Self::get).unwrap_or(0)
|
|
}
|
|
}
|
|
)+
|
|
};
|
|
}
|
|
|
|
non_zero_option! {
|
|
#[stable(feature = "nonzero", since = "1.28.0")] crate::num::NonZeroU8;
|
|
#[stable(feature = "nonzero", since = "1.28.0")] crate::num::NonZeroU16;
|
|
#[stable(feature = "nonzero", since = "1.28.0")] crate::num::NonZeroU32;
|
|
#[stable(feature = "nonzero", since = "1.28.0")] crate::num::NonZeroU64;
|
|
#[stable(feature = "nonzero", since = "1.28.0")] crate::num::NonZeroU128;
|
|
#[stable(feature = "nonzero", since = "1.28.0")] crate::num::NonZeroUsize;
|
|
#[stable(feature = "signed_nonzero", since = "1.34.0")] crate::num::NonZeroI8;
|
|
#[stable(feature = "signed_nonzero", since = "1.34.0")] crate::num::NonZeroI16;
|
|
#[stable(feature = "signed_nonzero", since = "1.34.0")] crate::num::NonZeroI32;
|
|
#[stable(feature = "signed_nonzero", since = "1.34.0")] crate::num::NonZeroI64;
|
|
#[stable(feature = "signed_nonzero", since = "1.34.0")] crate::num::NonZeroI128;
|
|
#[stable(feature = "signed_nonzero", since = "1.34.0")] crate::num::NonZeroIsize;
|
|
}
|
|
|
|
#[stable(feature = "nonnull", since = "1.25.0")]
|
|
impl<T> SpecOptionPartialEq for crate::ptr::NonNull<T> {
|
|
#[inline]
|
|
fn eq(l: &Option<Self>, r: &Option<Self>) -> bool {
|
|
l.map(Self::as_ptr).unwrap_or_else(|| crate::ptr::null_mut())
|
|
== r.map(Self::as_ptr).unwrap_or_else(|| crate::ptr::null_mut())
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl SpecOptionPartialEq for cmp::Ordering {
|
|
#[inline]
|
|
fn eq(l: &Option<Self>, r: &Option<Self>) -> bool {
|
|
l.map_or(2, |x| x as i8) == r.map_or(2, |x| x as i8)
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// The Option Iterators
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
#[derive(Clone, Debug)]
|
|
struct Item<A> {
|
|
opt: Option<A>,
|
|
}
|
|
|
|
impl<A> Iterator for Item<A> {
|
|
type Item = A;
|
|
|
|
#[inline]
|
|
fn next(&mut self) -> Option<A> {
|
|
self.opt.take()
|
|
}
|
|
|
|
#[inline]
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
match self.opt {
|
|
Some(_) => (1, Some(1)),
|
|
None => (0, Some(0)),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<A> DoubleEndedIterator for Item<A> {
|
|
#[inline]
|
|
fn next_back(&mut self) -> Option<A> {
|
|
self.opt.take()
|
|
}
|
|
}
|
|
|
|
impl<A> ExactSizeIterator for Item<A> {}
|
|
impl<A> FusedIterator for Item<A> {}
|
|
unsafe impl<A> TrustedLen for Item<A> {}
|
|
|
|
/// An iterator over a reference to the [`Some`] variant of an [`Option`].
|
|
///
|
|
/// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.
|
|
///
|
|
/// This `struct` is created by the [`Option::iter`] function.
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[derive(Debug)]
|
|
pub struct Iter<'a, A: 'a> {
|
|
inner: Item<&'a A>,
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<'a, A> Iterator for Iter<'a, A> {
|
|
type Item = &'a A;
|
|
|
|
#[inline]
|
|
fn next(&mut self) -> Option<&'a A> {
|
|
self.inner.next()
|
|
}
|
|
#[inline]
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
self.inner.size_hint()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<'a, A> DoubleEndedIterator for Iter<'a, A> {
|
|
#[inline]
|
|
fn next_back(&mut self) -> Option<&'a A> {
|
|
self.inner.next_back()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<A> ExactSizeIterator for Iter<'_, A> {}
|
|
|
|
#[stable(feature = "fused", since = "1.26.0")]
|
|
impl<A> FusedIterator for Iter<'_, A> {}
|
|
|
|
#[unstable(feature = "trusted_len", issue = "37572")]
|
|
unsafe impl<A> TrustedLen for Iter<'_, A> {}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<A> Clone for Iter<'_, A> {
|
|
#[inline]
|
|
fn clone(&self) -> Self {
|
|
Iter { inner: self.inner.clone() }
|
|
}
|
|
}
|
|
|
|
/// An iterator over a mutable reference to the [`Some`] variant of an [`Option`].
|
|
///
|
|
/// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.
|
|
///
|
|
/// This `struct` is created by the [`Option::iter_mut`] function.
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[derive(Debug)]
|
|
pub struct IterMut<'a, A: 'a> {
|
|
inner: Item<&'a mut A>,
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<'a, A> Iterator for IterMut<'a, A> {
|
|
type Item = &'a mut A;
|
|
|
|
#[inline]
|
|
fn next(&mut self) -> Option<&'a mut A> {
|
|
self.inner.next()
|
|
}
|
|
#[inline]
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
self.inner.size_hint()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<'a, A> DoubleEndedIterator for IterMut<'a, A> {
|
|
#[inline]
|
|
fn next_back(&mut self) -> Option<&'a mut A> {
|
|
self.inner.next_back()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<A> ExactSizeIterator for IterMut<'_, A> {}
|
|
|
|
#[stable(feature = "fused", since = "1.26.0")]
|
|
impl<A> FusedIterator for IterMut<'_, A> {}
|
|
#[unstable(feature = "trusted_len", issue = "37572")]
|
|
unsafe impl<A> TrustedLen for IterMut<'_, A> {}
|
|
|
|
/// An iterator over the value in [`Some`] variant of an [`Option`].
|
|
///
|
|
/// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.
|
|
///
|
|
/// This `struct` is created by the [`Option::into_iter`] function.
|
|
#[derive(Clone, Debug)]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub struct IntoIter<A> {
|
|
inner: Item<A>,
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<A> Iterator for IntoIter<A> {
|
|
type Item = A;
|
|
|
|
#[inline]
|
|
fn next(&mut self) -> Option<A> {
|
|
self.inner.next()
|
|
}
|
|
#[inline]
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
self.inner.size_hint()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<A> DoubleEndedIterator for IntoIter<A> {
|
|
#[inline]
|
|
fn next_back(&mut self) -> Option<A> {
|
|
self.inner.next_back()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<A> ExactSizeIterator for IntoIter<A> {}
|
|
|
|
#[stable(feature = "fused", since = "1.26.0")]
|
|
impl<A> FusedIterator for IntoIter<A> {}
|
|
|
|
#[unstable(feature = "trusted_len", issue = "37572")]
|
|
unsafe impl<A> TrustedLen for IntoIter<A> {}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// FromIterator
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> {
|
|
/// Takes each element in the [`Iterator`]: if it is [`None`][Option::None],
|
|
/// no further elements are taken, and the [`None`][Option::None] is
|
|
/// returned. Should no [`None`][Option::None] occur, a container of type
|
|
/// `V` containing the values of each [`Option`] is returned.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Here is an example which increments every integer in a vector.
|
|
/// We use the checked variant of `add` that returns `None` when the
|
|
/// calculation would result in an overflow.
|
|
///
|
|
/// ```
|
|
/// let items = vec![0_u16, 1, 2];
|
|
///
|
|
/// let res: Option<Vec<u16>> = items
|
|
/// .iter()
|
|
/// .map(|x| x.checked_add(1))
|
|
/// .collect();
|
|
///
|
|
/// assert_eq!(res, Some(vec![1, 2, 3]));
|
|
/// ```
|
|
///
|
|
/// As you can see, this will return the expected, valid items.
|
|
///
|
|
/// Here is another example that tries to subtract one from another list
|
|
/// of integers, this time checking for underflow:
|
|
///
|
|
/// ```
|
|
/// let items = vec![2_u16, 1, 0];
|
|
///
|
|
/// let res: Option<Vec<u16>> = items
|
|
/// .iter()
|
|
/// .map(|x| x.checked_sub(1))
|
|
/// .collect();
|
|
///
|
|
/// assert_eq!(res, None);
|
|
/// ```
|
|
///
|
|
/// Since the last element is zero, it would underflow. Thus, the resulting
|
|
/// value is `None`.
|
|
///
|
|
/// Here is a variation on the previous example, showing that no
|
|
/// further elements are taken from `iter` after the first `None`.
|
|
///
|
|
/// ```
|
|
/// let items = vec![3_u16, 2, 1, 10];
|
|
///
|
|
/// let mut shared = 0;
|
|
///
|
|
/// let res: Option<Vec<u16>> = items
|
|
/// .iter()
|
|
/// .map(|x| { shared += x; x.checked_sub(2) })
|
|
/// .collect();
|
|
///
|
|
/// assert_eq!(res, None);
|
|
/// assert_eq!(shared, 6);
|
|
/// ```
|
|
///
|
|
/// Since the third element caused an underflow, no further elements were taken,
|
|
/// so the final value of `shared` is 6 (= `3 + 2 + 1`), not 16.
|
|
#[inline]
|
|
fn from_iter<I: IntoIterator<Item = Option<A>>>(iter: I) -> Option<V> {
|
|
// FIXME(#11084): This could be replaced with Iterator::scan when this
|
|
// performance bug is closed.
|
|
|
|
iter::try_process(iter.into_iter(), |i| i.collect())
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "try_trait_v2", issue = "84277")]
|
|
#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
|
|
impl<T> const ops::Try for Option<T> {
|
|
type Output = T;
|
|
type Residual = Option<convert::Infallible>;
|
|
|
|
#[inline]
|
|
fn from_output(output: Self::Output) -> Self {
|
|
Some(output)
|
|
}
|
|
|
|
#[inline]
|
|
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
|
|
match self {
|
|
Some(v) => ControlFlow::Continue(v),
|
|
None => ControlFlow::Break(None),
|
|
}
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "try_trait_v2", issue = "84277")]
|
|
#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
|
|
impl<T> const ops::FromResidual for Option<T> {
|
|
#[inline]
|
|
fn from_residual(residual: Option<convert::Infallible>) -> Self {
|
|
match residual {
|
|
None => None,
|
|
}
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "try_trait_v2_yeet", issue = "96374")]
|
|
impl<T> ops::FromResidual<ops::Yeet<()>> for Option<T> {
|
|
#[inline]
|
|
fn from_residual(ops::Yeet(()): ops::Yeet<()>) -> Self {
|
|
None
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "try_trait_v2_residual", issue = "91285")]
|
|
#[rustc_const_unstable(feature = "const_try", issue = "74935")]
|
|
impl<T> const ops::Residual<T> for Option<convert::Infallible> {
|
|
type TryType = Option<T>;
|
|
}
|
|
|
|
impl<T> Option<Option<T>> {
|
|
/// Converts from `Option<Option<T>>` to `Option<T>`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// let x: Option<Option<u32>> = Some(Some(6));
|
|
/// assert_eq!(Some(6), x.flatten());
|
|
///
|
|
/// let x: Option<Option<u32>> = Some(None);
|
|
/// assert_eq!(None, x.flatten());
|
|
///
|
|
/// let x: Option<Option<u32>> = None;
|
|
/// assert_eq!(None, x.flatten());
|
|
/// ```
|
|
///
|
|
/// Flattening only removes one level of nesting at a time:
|
|
///
|
|
/// ```
|
|
/// let x: Option<Option<Option<u32>>> = Some(Some(Some(6)));
|
|
/// assert_eq!(Some(Some(6)), x.flatten());
|
|
/// assert_eq!(Some(6), x.flatten().flatten());
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "option_flattening", since = "1.40.0")]
|
|
#[rustc_const_unstable(feature = "const_option", issue = "67441")]
|
|
pub const fn flatten(self) -> Option<T> {
|
|
match self {
|
|
Some(inner) => inner,
|
|
None => None,
|
|
}
|
|
}
|
|
}
|