diff --git a/library/core/src/option.rs b/library/core/src/option.rs index 13de1cb3092..b7af3ea8c1a 100644 --- a/library/core/src/option.rs +++ b/library/core/src/option.rs @@ -49,6 +49,8 @@ //! no "null" references. Instead, Rust has *optional* pointers, like //! the optional owned box, [`Option`]`<`[`Box`]`>`. //! +//! [`Box`]: ../../std/boxed/struct.Box.html +//! //! The following example uses [`Option`] to create an optional box of //! [`i32`]. Notice that in order to use the inner [`i32`] value, the //! `check_optional` function first needs to use pattern matching to @@ -83,6 +85,10 @@ //! * [`ptr::NonNull`] //! * `#[repr(transparent)]` struct around one of the types in this list. //! +//! [`Box`]: ../../std/boxed/struct.Box.html +//! [`num::NonZero*`]: crate::num +//! [`ptr::NonNull`]: crate::ptr::NonNull +//! //! This is called the "null pointer optimization" or NPO. //! //! It is further guaranteed that, for the cases above, one can @@ -90,6 +96,339 @@ //! from `Some::(_)` to `T` (but transmuting `None::` to `T` //! is undefined behaviour). //! +//! # Method overview +//! +//! In addition to working with pattern matching, [`Option`] provides a wide +//! variety of different methods. +//! +//! ## Querying the variant +//! +//! The [`is_some`] and [`is_none`] methods return [`true`] if the [`Option`] +//! is [`Some`] or [`None`], respectively. +//! +//! [`is_none`]: Option::is_none +//! [`is_some`]: Option::is_some +//! +//! ## Adapters for working with references +//! +//! * [`as_ref`] converts from `&Option` to `Option<&T>` +//! * [`as_mut`] converts from `&mut Option` to `Option<&mut T>` +//! * [`as_deref`] converts from `&Option` to `Option<&T::Target>` +//! * [`as_deref_mut`] converts from `&mut Option` to +//! `Option<&mut T::Target>` +//! * [`as_pin_ref`] converts from [`Pin`]`<&Option>` to +//! `Option<`[`Pin`]`<&T>>` +//! * [`as_pin_mut`] converts from [`Pin`]`<&mut Option>` to +//! `Option<`[`Pin`]`<&mut T>>` +//! +//! [`as_deref`]: Option::as_deref +//! [`as_deref_mut`]: Option::as_deref_mut +//! [`as_mut`]: Option::as_mut +//! [`as_pin_mut`]: Option::as_pin_mut +//! [`as_pin_ref`]: Option::as_pin_ref +//! [`as_ref`]: Option::as_ref +//! +//! ## Extracting the contained value +//! +//! These methods extract the contained value in an [`Option`] when it +//! is the [`Some`] variant. If the [`Option`] is [`None`]: +//! +//! * [`expect`] panics with a provided custom message +//! * [`unwrap`] panics with a generic message +//! * [`unwrap_or`] returns the provided default value +//! * [`unwrap_or_default`] returns the default value of the type `T` +//! (which must implement the [`Default`] trait) +//! * [`unwrap_or_else`] returns the result of evaluating the provided +//! function +//! +//! [`expect`]: Option::expect +//! [`unwrap`]: Option::unwrap +//! [`unwrap_or`]: Option::unwrap_or +//! [`unwrap_or_default`]: Option::unwrap_or_default +//! [`unwrap_or_else`]: Option::unwrap_or_else +//! +//! ## Transforming contained values +//! +//! These methods transform [`Option`] to [`Result`]: +//! +//! * [`ok_or`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to +//! [`Err(err)`] using the provided default `err` value +//! * [`ok_or_else`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to +//! a value of [`Err`] using the provided function +//! * [`transpose`] transposes an [`Option`] of a [`Result`] into a +//! [`Result`] of an [`Option`] +//! +//! [`Err(err)`]: Err +//! [`Ok(v)`]: Ok +//! [`Some(v)`]: Some +//! [`ok_or`]: Option::ok_or +//! [`ok_or_else`]: Option::ok_or_else +//! [`transpose`]: Option::transpose +//! +//! These methods transform the [`Some`] variant: +//! +//! * [`filter`] calls the provided predicate function on the contained +//! value `t` if the [`Option`] is [`Some(t)`], and returns [`Some(t)`] +//! if the function returns `true`; otherwise, returns [`None`] +//! * [`flatten`] removes one level of nesting from an +//! [`Option>`] +//! * [`map`] transforms [`Option`] to [`Option`] by applying the +//! provided function to the contained value of [`Some`] and leaving +//! [`None`] values unchanged +//! +//! [`Some(t)`]: Some +//! [`filter`]: Option::filter +//! [`flatten`]: Option::flatten +//! [`map`]: Option::map +//! +//! These methods transform [`Option`] to a value of a possibly +//! different type `U`: +//! +//! * [`map_or`] applies the provided function to the contained value of +//! [`Some`], or returns the provided default value if the [`Option`] is +//! [`None`] +//! * [`map_or_else`] applies the provided function to the contained value +//! of [`Some`], or returns the result of evaluating the provided +//! fallback function if the [`Option`] is [`None`] +//! +//! [`map_or`]: Option::map_or +//! [`map_or_else`]: Option::map_or_else +//! +//! These methods combine the [`Some`] variants of two [`Option`] values: +//! +//! * [`zip`] returns [`Some((s, o))`] if `self` is [`Some(s)`] and the +//! provided [`Option`] value is [`Some(o)`]; otherwise, returns [`None`] +//! * [`zip_with`] calls the provided function `f` and returns +//! [`Some(f(s, o))`] if `self` is [`Some(s)`] and the provided +//! [`Option`] value is [`Some(o)`]; otherwise, returns [`None`] +//! +//! [`Some(f(s, o))`]: Some +//! [`Some(o)`]: Some +//! [`Some(s)`]: Some +//! [`Some((s, o))`]: Some +//! [`zip`]: Option::zip +//! [`zip_with`]: Option::zip_with +//! +//! ## Boolean operators +//! +//! These methods treat the [`Option`] as a boolean value, where [`Some`] +//! acts like [`true`] and [`None`] acts like [`false`]. There are two +//! categories of these methods: ones that take an [`Option`] as input, and +//! ones that take a function as input (to be lazily evaluated). +//! +//! The [`and`], [`or`], and [`xor`] methods take another [`Option`] as +//! input, and produce an [`Option`] as output. Only the [`and`] method can +//! produce an [`Option`] value having a different inner type `U` than +//! [`Option`]. +//! +//! | method | self | input | output | +//! |---------|-----------|-----------|-----------| +//! | [`and`] | `None` | (ignored) | `None` | +//! | [`and`] | `Some(x)` | `None` | `None` | +//! | [`and`] | `Some(x)` | `Some(y)` | `Some(y)` | +//! | [`or`] | `None` | `None` | `None` | +//! | [`or`] | `None` | `Some(y)` | `Some(y)` | +//! | [`or`] | `Some(x)` | (ignored) | `Some(x)` | +//! | [`xor`] | `None` | `None` | `None` | +//! | [`xor`] | `None` | `Some(y)` | `Some(y)` | +//! | [`xor`] | `Some(x)` | `None` | `Some(x)` | +//! | [`xor`] | `Some(x)` | `Some(y)` | `None` | +//! +//! [`and`]: Option::and +//! [`or`]: Option::or +//! [`xor`]: Option::xor +//! +//! The [`and_then`] and [`or_else`] methods take a function as input, and +//! only evaluate the function when they need to produce a new value. Only +//! the [`and_then`] method can produce an [`Option`] value having a +//! different inner type `U` than [`Option`]. +//! +//! | method | self | function input | function result | output | +//! |--------------|-----------|----------------|-----------------|-----------| +//! | [`and_then`] | `None` | (not provided) | (not evaluated) | `None` | +//! | [`and_then`] | `Some(x)` | `x` | `None` | `None` | +//! | [`and_then`] | `Some(x)` | `x` | `Some(y)` | `Some(y)` | +//! | [`or_else`] | `None` | (not provided) | `None` | `None` | +//! | [`or_else`] | `None` | (not provided) | `Some(y)` | `Some(y)` | +//! | [`or_else`] | `Some(x)` | (not provided) | (not evaluated) | `Some(x)` | +//! +//! [`and_then`]: Option::and_then +//! [`or_else`]: Option::or_else +//! +//! This is an example of using methods like [`and_then`] and [`or`] in a +//! pipeline of method calls. Early stages of the pipeline pass failure +//! values ([`None`]) through unchanged, and continue processing on +//! success values ([`Some`]). Toward the end, [`or`] substitutes an error +//! message if it receives [`None`]. +//! +//! ``` +//! # use std::collections::BTreeMap; +//! let mut bt = BTreeMap::new(); +//! bt.insert(20u8, "foo"); +//! bt.insert(42u8, "bar"); +//! let res = vec![0u8, 1, 11, 200, 22] +//! .into_iter() +//! .map(|x| { +//! // `checked_sub()` returns `None` on error +//! x.checked_sub(1) +//! // same with `checked_mul()` +//! .and_then(|x| x.checked_mul(2)) +//! // `BTreeMap::get` returns `None` on error +//! .and_then(|x| bt.get(&x)) +//! // Substitute an error message if we have `None` so far +//! .or(Some(&"error!")) +//! .copied() +//! // Won't panic because we unconditionally used `Some` above +//! .unwrap() +//! }) +//! .collect::>(); +//! assert_eq!(res, ["error!", "error!", "foo", "error!", "bar"]); +//! ``` +//! +//! ## Iterating over `Option` +//! +//! An [`Option`] can be iterated over. This can be helpful if you need an +//! iterator that is conditionally empty. The iterator will either produce +//! a single value (when the [`Option`] is [`Some`]), or produce no values +//! (when the [`Option`] is [`None`]). For example, [`into_iter`] acts like +//! [`once(v)`] if the [`Option`] is [`Some(v)`], and like [`empty()`] if +//! the [`Option`] is [`None`]. +//! +//! [`Some(v)`]: Some +//! [`empty()`]: crate::iter::empty +//! [`once(v)`]: crate::iter::once +//! +//! Iterators over [`Option`] come in three types: +//! +//! * [`into_iter`] consumes the [`Option`] and produces the contained +//! value +//! * [`iter`] produces an immutable reference of type `&T` to the +//! contained value +//! * [`iter_mut`] produces a mutable reference of type `&mut T` to the +//! contained value +//! +//! [`into_iter`]: Option::into_iter +//! [`iter`]: Option::iter +//! [`iter_mut`]: Option::iter_mut +//! +//! An iterator over [`Option`] can be useful when chaining iterators, for +//! example, to conditionally insert items. (It's not always necessary to +//! explicitly call an iterator constructor: many [`Iterator`] methods that +//! accept other iterators will also accept iterable types that implement +//! [`IntoIterator`], which includes [`Option`].) +//! +//! ``` +//! let yep = Some(42); +//! let nope = None; +//! // chain() already calls into_iter(), so we don't have to do so +//! let nums: Vec = (0..4).chain(yep).chain(4..8).collect(); +//! assert_eq!(nums, [0, 1, 2, 3, 42, 4, 5, 6, 7]); +//! let nums: Vec = (0..4).chain(nope).chain(4..8).collect(); +//! assert_eq!(nums, [0, 1, 2, 3, 4, 5, 6, 7]); +//! ``` +//! +//! One reason to chain iterators in this way is that a function returning +//! `impl Iterator` must have all possible return values be of the same +//! concrete type. Chaining an iterated [`Option`] can help with that. +//! +//! ``` +//! fn make_iter(do_insert: bool) -> impl Iterator { +//! // Explicit returns to illustrate return types matching +//! match do_insert { +//! true => return (0..4).chain(Some(42)).chain(4..8), +//! false => return (0..4).chain(None).chain(4..8), +//! } +//! } +//! println!("{:?}", make_iter(true).collect::>()); +//! println!("{:?}", make_iter(false).collect::>()); +//! ``` +//! +//! If we try to do the same thing, but using [`once()`] and [`empty()`], +//! we can't return `impl Iterator` anymore because the concrete types of +//! the return values differ. +//! +//! [`empty()`]: crate::iter::empty +//! [`once()`]: crate::iter::once +//! +//! ```compile_fail,E0308 +//! # use std::iter::{empty, once}; +//! // This won't compile because all possible returns from the function +//! // must have the same concrete type. +//! fn make_iter(do_insert: bool) -> impl Iterator { +//! // Explicit returns to illustrate return types not matching +//! match x { +//! true => return (0..4).chain(once(42)).chain(4..8), +//! false => return (0..4).chain(empty()).chain(4..8), +//! } +//! } +//! ``` +//! +//! ## 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 +//! +//! ``` +//! let v = vec![Some(2), Some(4), None, Some(8)]; +//! let res: Option> = v.into_iter().collect(); +//! assert_eq!(res, None); +//! let v = vec![Some(2), Some(4), Some(8)]; +//! let res: Option> = 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 +//! [impl-Sum]: Option#impl-Sum%3COption%3CU%3E%3E +//! +//! ``` +//! let v = vec![None, Some(1), Some(2), Some(3)]; +//! let res: Option = v.into_iter().sum(); +//! assert_eq!(res, None); +//! let v = vec![Some(1), Some(2), Some(21)]; +//! let res: Option = 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`]: +//! +//! * [`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`]: @@ -141,11 +480,6 @@ //! None => println!("there are no animals :("), //! } //! ``` -//! -//! [`Box`]: ../../std/boxed/struct.Box.html -//! [`Box`]: ../../std/boxed/struct.Box.html -//! [`num::NonZero*`]: crate::num -//! [`ptr::NonNull`]: crate::ptr::NonNull #![stable(feature = "rust1", since = "1.0.0")] diff --git a/library/core/src/result.rs b/library/core/src/result.rs index 325efe721e3..53aaa5219b1 100644 --- a/library/core/src/result.rs +++ b/library/core/src/result.rs @@ -224,6 +224,250 @@ //! [`Ok(T)`]: Ok //! [`Err(E)`]: Err //! [`io::Error`]: ../../std/io/struct.Error.html +//! +//! # Method overview +//! +//! In addition to working with pattern matching, [`Result`] provides a +//! wide variety of different methods. +//! +//! ## Querying the variant +//! +//! The [`is_ok`] and [`is_err`] methods return [`true`] if the [`Result`] +//! is [`Ok`] or [`Err`], respectively. +//! +//! [`is_err`]: Result::is_err +//! [`is_ok`]: Result::is_ok +//! +//! ## Adapters for working with references +//! +//! * [`as_ref`] converts from `&Result` to `Result<&T, &E>` +//! * [`as_mut`] converts from `&mut Result` to `Result<&mut T, &mut E>` +//! * [`as_deref`] converts from `&Result` to `Result<&T::Target, &E>` +//! * [`as_deref_mut`] converts from `&mut Result` to +//! `Result<&mut T::Target, &mut E>` +//! +//! [`as_deref`]: Result::as_deref +//! [`as_deref_mut`]: Result::as_deref_mut +//! [`as_mut`]: Result::as_mut +//! [`as_ref`]: Result::as_ref +//! +//! ## Extracting contained values +//! +//! These methods extract the contained value in a [`Result`] when it +//! is the [`Ok`] variant. If the [`Result`] is [`Err`]: +//! +//! * [`expect`] panics with a provided custom message +//! * [`unwrap`] panics with a generic message +//! * [`unwrap_or`] returns the provided default value +//! * [`unwrap_or_default`] returns the default value of the type `T` +//! (which must implement the [`Default`] trait) +//! * [`unwrap_or_else`] returns the result of evaluating the provided +//! function +//! +//! The panicking methods [`expect`] and [`unwrap`] require `E` to +//! implement the [`Debug`] trait. +//! +//! [`Debug`]: crate::fmt::Debug +//! [`expect`]: Result::expect +//! [`unwrap`]: Result::unwrap +//! [`unwrap_or`]: Result::unwrap_or +//! [`unwrap_or_default`]: Result::unwrap_or_default +//! [`unwrap_or_else`]: Result::unwrap_or_else +//! +//! These methods extract the contained value in a [`Result`] when it +//! is the [`Err`] variant. They require `T` to implement the [`Debug`] +//! trait. If the [`Result`] is [`Ok`]: +//! +//! * [`expect_err`] panics with a provided custom message +//! * [`unwrap_err`] panics with a generic message +//! +//! [`Debug`]: crate::fmt::Debug +//! [`expect_err`]: Result::expect_err +//! [`unwrap_err`]: Result::unwrap_err +//! +//! ## Transforming contained values +//! +//! These methods transform [`Result`] to [`Option`]: +//! +//! * [`err`][Result::err] transforms [`Result`] into [`Option`], +//! mapping [`Err(e)`] to [`Some(e)`] and [`Ok(v)`] to [`None`] +//! * [`ok`][Result::ok] transforms [`Result`] into [`Option`], +//! mapping [`Ok(v)`] to [`Some(v)`] and [`Err(e)`] to [`None`] +//! * [`transpose`] transposes a [`Result`] of an [`Option`] into an +//! [`Option`] of a [`Result`] +//! +// Do NOT add link reference definitions for `err` or `ok`, because they +// will generate numerous incorrect URLs for `Err` and `Ok` elsewhere, due +// to case folding. +//! +//! [`Err(e)`]: Err +//! [`Ok(v)`]: Ok +//! [`Some(e)`]: Option::Some +//! [`Some(v)`]: Option::Some +//! [`transpose`]: Result::transpose +//! +//! This method transforms the contained value of the [`Ok`] variant: +//! +//! * [`map`] transforms [`Result`] into [`Result`] by applying +//! the provided function to the contained value of [`Ok`] and leaving +//! [`Err`] values unchanged +//! +//! [`map`]: Result::map +//! +//! This method transforms the contained value of the [`Err`] variant: +//! +//! * [`map_err`] transforms [`Result`] into [`Result`] by +//! applying the provided function to the contained value of [`Err`] and +//! leaving [`Ok`] values unchanged +//! +//! [`map_err`]: Result::map_err +//! +//! These methods transform a [`Result`] into a value of a possibly +//! different type `U`: +//! +//! * [`map_or`] applies the provided function to the contained value of +//! [`Ok`], or returns the provided default value if the [`Result`] is +//! [`Err`] +//! * [`map_or_else`] applies the provided function to the contained value +//! of [`Ok`], or applies the provided fallback function to the contained +//! value of [`Err`] +//! +//! [`map_or`]: Result::map_or +//! [`map_or_else`]: Result::map_or_else +//! +//! ## Boolean operators +//! +//! These methods treat the [`Result`] as a boolean value, where [`Ok`] +//! acts like [`true`] and [`Err`] acts like [`false`]. There are two +//! categories of these methods: ones that take a [`Result`] as input, and +//! ones that take a function as input (to be lazily evaluated). +//! +//! The [`and`] and [`or`] methods take another [`Result`] as input, and +//! produce a [`Result`] as output. The [`and`] method can produce a +//! [`Result`] value having a different inner type `U` than +//! [`Result`]. The [`or`] method can produce a [`Result`] +//! value having a different error type `F` than [`Result`]. +//! +//! | method | self | input | output | +//! |---------|----------|-----------|----------| +//! | [`and`] | `Err(e)` | (ignored) | `Err(e)` | +//! | [`and`] | `Ok(x)` | `Err(d)` | `Err(d)` | +//! | [`and`] | `Ok(x)` | `Ok(y)` | `Ok(y)` | +//! | [`or`] | `Err(e)` | `Err(d)` | `Err(d)` | +//! | [`or`] | `Err(e)` | `Ok(y)` | `Ok(y)` | +//! | [`or`] | `Ok(x)` | (ignored) | `Ok(x)` | +//! +//! [`and`]: Result::and +//! [`or`]: Result::or +//! +//! The [`and_then`] and [`or_else`] methods take a function as input, and +//! only evaluate the function when they need to produce a new value. The +//! [`and_then`] method can produce a [`Result`] value having a +//! different inner type `U` than [`Result`]. The [`or_else`] method +//! can produce a [`Result`] value having a different error type `F` +//! than [`Result`]. +//! +//! | method | self | function input | function result | output | +//! |--------------|----------|----------------|-----------------|----------| +//! | [`and_then`] | `Err(e)` | (not provided) | (not evaluated) | `Err(e)` | +//! | [`and_then`] | `Ok(x)` | `x` | `Err(d)` | `Err(d)` | +//! | [`and_then`] | `Ok(x)` | `x` | `Ok(y)` | `Ok(y)` | +//! | [`or_else`] | `Err(e)` | `e` | `Err(d)` | `Err(d)` | +//! | [`or_else`] | `Err(e)` | `e` | `Ok(y)` | `Ok(y)` | +//! | [`or_else`] | `Ok(x)` | (not provided) | (not evaluated) | `Ok(x)` | +//! +//! [`and_then`]: Result::and_then +//! [`or_else`]: Result::or_else +//! +//! ## Iterating over `Result` +//! +//! A [`Result`] can be iterated over. This can be helpful if you need an +//! iterator that is conditionally empty. The iterator will either produce +//! a single value (when the [`Result`] is [`Ok`]), or produce no values +//! (when the [`Result`] is [`Err`]). For example, [`into_iter`] acts like +//! [`once(v)`] if the [`Result`] is [`Ok(v)`], and like [`empty()`] if the +//! [`Result`] is [`Err`]. +//! +//! [`Ok(v)`]: Ok +//! [`empty()`]: crate::iter::empty +//! [`once(v)`]: crate::iter::once +//! +//! Iterators over [`Result`] come in three types: +//! +//! * [`into_iter`] consumes the [`Result`] and produces the contained +//! value +//! * [`iter`] produces an immutable reference of type `&T` to the +//! contained value +//! * [`iter_mut`] produces a mutable reference of type `&mut T` to the +//! contained value +//! +//! See [Iterating over `Option`] for examples of how this can be useful. +//! +//! [Iterating over `Option`]: crate::option#iterating-over-option +//! [`into_iter`]: Result::into_iter +//! [`iter`]: Result::iter +//! [`iter_mut`]: Result::iter_mut +//! +//! You might want to use an iterator chain to do multiple instances of an +//! operation that can fail, but would like to ignore failures while +//! continuing to process the successful results. In this example, we take +//! advantage of the iterable nature of [`Result`] to select only the +//! [`Ok`] values using [`flatten`][Iterator::flatten]. +//! +//! ``` +//! # use std::str::FromStr; +//! let mut results = vec![]; +//! let mut errs = vec![]; +//! let nums: Vec<_> = vec!["17", "not a number", "99", "-27", "768"] +//! .into_iter() +//! .map(u8::from_str) +//! // Save clones of the raw `Result` values to inspect +//! .inspect(|x| results.push(x.clone())) +//! // Challenge: explain how this captures only the `Err` values +//! .inspect(|x| errs.extend(x.clone().err())) +//! .flatten() +//! .collect(); +//! assert_eq!(errs.len(), 3); +//! assert_eq!(nums, [17, 99]); +//! println!("results {:?}", results); +//! println!("errs {:?}", errs); +//! println!("nums {:?}", nums); +//! ``` +//! +//! ## Collecting into `Result` +//! +//! [`Result`] implements the [`FromIterator`][impl-FromIterator] trait, +//! which allows an iterator over [`Result`] values to be collected into a +//! [`Result`] of a collection of each contained value of the original +//! [`Result`] values, or [`Err`] if any of the elements was [`Err`]. +//! +//! [impl-FromIterator]: Result#impl-FromIterator%3CResult%3CA%2C%20E%3E%3E +//! +//! ``` +//! let v = vec![Ok(2), Ok(4), Err("err!"), Ok(8)]; +//! let res: Result, &str> = v.into_iter().collect(); +//! assert_eq!(res, Err("err!")); +//! let v = vec![Ok(2), Ok(4), Ok(8)]; +//! let res: Result, &str> = v.into_iter().collect(); +//! assert_eq!(res, Ok(vec![2, 4, 8])); +//! ``` +//! +//! [`Result`] also implements the [`Product`][impl-Product] and +//! [`Sum`][impl-Sum] traits, allowing an iterator over [`Result`] values +//! to provide the [`product`][Iterator::product] and +//! [`sum`][Iterator::sum] methods. +//! +//! [impl-Product]: Result#impl-Product%3CResult%3CU%2C%20E%3E%3E +//! [impl-Sum]: Result#impl-Sum%3CResult%3CU%2C%20E%3E%3E +//! +//! ``` +//! let v = vec![Err("error!"), Ok(1), Ok(2), Ok(3), Err("foo")]; +//! let res: Result = v.into_iter().sum(); +//! assert_eq!(res, Err("error!")); +//! let v: Vec> = vec![Ok(1), Ok(2), Ok(21)]; +//! let res: Result = v.into_iter().product(); +//! assert_eq!(res, Ok(42)); +//! ``` #![stable(feature = "rust1", since = "1.0.0")]