732 lines
20 KiB
Rust
732 lines
20 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Optionally nullable values (`Option` type)
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//!
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//! Type `Option` represents an optional value.
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//!
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//! Every `Option<T>` value can either be `Some(T)` or `None`. Where in other
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//! languages you might use a nullable type, in Rust you would use an option
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//! type.
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//!
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//! Options are most commonly used 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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//! # Example
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//!
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//! ```
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//! let msg = Some(~"howdy");
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//!
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//! // Take a reference to the contained string
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//! match msg {
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//! Some(ref m) => println!("{}", *m),
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//! None => ()
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//! }
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//!
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//! // Remove the contained string, destroying the Option
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//! let unwrapped_msg = match msg {
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//! Some(m) => m,
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//! None => ~"default message"
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//! };
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//! ```
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use any::Any;
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use clone::Clone;
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use cmp::{Eq, TotalEq, TotalOrd};
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use default::Default;
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use iter::{Iterator, DoubleEndedIterator, FromIterator, ExactSize};
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use kinds::Send;
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use mem;
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use vec;
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/// The option type
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#[deriving(Clone, Eq, Ord, TotalEq, TotalOrd, Show)]
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pub enum Option<T> {
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/// No value
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None,
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/// Some value `T`
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Some(T)
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}
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/////////////////////////////////////////////////////////////////////////////
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// Type implementation
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/////////////////////////////////////////////////////////////////////////////
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impl<T> Option<T> {
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/////////////////////////////////////////////////////////////////////////
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// Querying the contained values
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/////////////////////////////////////////////////////////////////////////
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/// Returns true if the option contains a `Some` value
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#[inline]
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pub fn is_some(&self) -> bool {
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match *self {
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Some(_) => true,
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None => false
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}
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}
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/// Returns true if the option equals `None`
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#[inline]
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pub fn is_none(&self) -> bool {
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!self.is_some()
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}
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/////////////////////////////////////////////////////////////////////////
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// Adapter for working with references
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/////////////////////////////////////////////////////////////////////////
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/// Convert from `Option<T>` to `Option<&T>`
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#[inline]
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pub fn as_ref<'r>(&'r self) -> Option<&'r T> {
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match *self { Some(ref x) => Some(x), None => None }
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}
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/// Convert from `Option<T>` to `Option<&mut T>`
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#[inline]
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pub fn as_mut<'r>(&'r mut self) -> Option<&'r mut T> {
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match *self { Some(ref mut x) => Some(x), None => None }
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}
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/// Convert from `Option<T>` to `&[T]` (without copying)
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#[inline]
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pub fn as_slice<'r>(&'r self) -> &'r [T] {
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match *self {
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Some(ref x) => vec::ref_slice(x),
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None => &[]
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}
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}
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/// Convert from `Option<T>` to `&mut [T]` (without copying)
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#[inline]
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pub fn as_mut_slice<'r>(&'r mut self) -> &'r mut [T] {
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match *self {
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Some(ref mut x) => vec::mut_ref_slice(x),
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None => &mut []
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}
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}
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/////////////////////////////////////////////////////////////////////////
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// Getting to contained values
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/////////////////////////////////////////////////////////////////////////
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/// Unwraps an option, yielding the content of a `Some`
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/// Fails if the value is a `None` with a custom failure message provided by `msg`.
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#[inline]
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pub fn expect<M: Any + Send>(self, msg: M) -> T {
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match self {
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Some(val) => val,
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None => fail!(msg),
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}
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}
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/// Moves a value out of an option type and returns it.
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///
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/// Useful primarily for getting strings, vectors and unique pointers out
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/// of option types without copying them.
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///
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/// # Failure
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///
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/// Fails if the value equals `None`.
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///
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/// # Safety note
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///
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/// In general, because this function may fail, its use is discouraged.
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/// Instead, prefer to use pattern matching and handle the `None`
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/// case explicitly.
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#[inline]
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pub fn unwrap(self) -> T {
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match self {
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Some(val) => val,
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None => fail!("called `Option::unwrap()` on a `None` value"),
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}
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}
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/// Returns the contained value or a default
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#[inline]
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pub fn unwrap_or(self, def: T) -> T {
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match self {
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Some(x) => x,
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None => def
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}
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}
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/// Returns the contained value or computes it from a closure
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#[inline]
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pub fn unwrap_or_else(self, f: || -> T) -> T {
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match self {
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Some(x) => x,
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None => f()
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}
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}
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/////////////////////////////////////////////////////////////////////////
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// Transforming contained values
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/////////////////////////////////////////////////////////////////////////
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/// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value.
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#[inline]
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pub fn map<U>(self, f: |T| -> U) -> Option<U> {
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match self { Some(x) => Some(f(x)), None => None }
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}
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/// Applies a function to the contained value or returns a default.
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#[inline]
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pub fn map_or<U>(self, def: U, f: |T| -> U) -> U {
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match self { None => def, Some(t) => f(t) }
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}
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/// Apply a function to the contained value or do nothing.
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/// Returns true if the contained value was mutated.
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pub fn mutate(&mut self, f: |T| -> T) -> bool {
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if self.is_some() {
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*self = Some(f(self.take_unwrap()));
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true
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} else { false }
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}
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/// Apply a function to the contained value or set it to a default.
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/// Returns true if the contained value was mutated, or false if set to the default.
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pub fn mutate_or_set(&mut self, def: T, f: |T| -> T) -> bool {
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if self.is_some() {
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*self = Some(f(self.take_unwrap()));
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true
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} else {
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*self = Some(def);
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false
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}
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}
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/////////////////////////////////////////////////////////////////////////
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// Iterator constructors
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/////////////////////////////////////////////////////////////////////////
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/// Return an iterator over the possibly contained value
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#[inline]
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pub fn iter<'r>(&'r self) -> Item<&'r T> {
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Item{opt: self.as_ref()}
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}
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/// Return a mutable iterator over the possibly contained value
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#[inline]
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pub fn mut_iter<'r>(&'r mut self) -> Item<&'r mut T> {
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Item{opt: self.as_mut()}
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}
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/// Return a consuming iterator over the possibly contained value
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#[inline]
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pub fn move_iter(self) -> Item<T> {
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Item{opt: self}
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}
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/////////////////////////////////////////////////////////////////////////
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// Boolean operations on the values, eager and lazy
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/////////////////////////////////////////////////////////////////////////
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/// Returns `None` if the option is `None`, otherwise returns `optb`.
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#[inline]
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pub fn and<U>(self, optb: Option<U>) -> Option<U> {
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match self {
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Some(_) => optb,
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None => None,
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}
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}
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/// Returns `None` if the option is `None`, otherwise calls `f` with the
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/// wrapped value and returns the result.
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#[inline]
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pub fn and_then<U>(self, f: |T| -> Option<U>) -> Option<U> {
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match self {
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Some(x) => f(x),
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None => None,
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}
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}
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/// Returns the option if it contains a value, otherwise returns `optb`.
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#[inline]
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pub fn or(self, optb: Option<T>) -> Option<T> {
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match self {
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Some(_) => self,
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None => optb
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}
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}
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/// Returns the option if it contains a value, otherwise calls `f` and
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/// returns the result.
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#[inline]
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pub fn or_else(self, f: || -> Option<T>) -> Option<T> {
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match self {
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Some(_) => self,
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None => f(),
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}
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}
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/////////////////////////////////////////////////////////////////////////
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// Misc
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/////////////////////////////////////////////////////////////////////////
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/// Take the value out of the option, leaving a `None` in its place.
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#[inline]
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pub fn take(&mut self) -> Option<T> {
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mem::replace(self, None)
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}
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/// Filters an optional value using a given function.
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#[inline(always)]
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pub fn filtered(self, f: |t: &T| -> bool) -> Option<T> {
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match self {
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Some(x) => if f(&x) {Some(x)} else {None},
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None => None
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}
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}
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/// Applies a function zero or more times until the result is `None`.
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#[inline]
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pub fn while_some(self, f: |v: T| -> Option<T>) {
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let mut opt = self;
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loop {
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match opt {
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Some(x) => opt = f(x),
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None => break
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}
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}
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}
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/////////////////////////////////////////////////////////////////////////
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// Common special cases
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/////////////////////////////////////////////////////////////////////////
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/// The option dance. Moves a value out of an option type and returns it,
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/// replacing the original with `None`.
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///
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/// # Failure
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///
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/// Fails if the value equals `None`.
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#[inline]
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pub fn take_unwrap(&mut self) -> T {
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match self.take() {
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Some(x) => x,
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None => fail!("called `Option::take_unwrap()` on a `None` value")
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}
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}
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/// Gets an immutable reference to the value inside an option.
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///
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/// # Failure
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///
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/// Fails if the value equals `None`
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///
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/// # Safety note
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///
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/// In general, because this function may fail, its use is discouraged
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/// (calling `get` on `None` is akin to dereferencing a null pointer).
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/// Instead, prefer to use pattern matching and handle the `None`
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/// case explicitly.
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#[inline]
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pub fn get_ref<'a>(&'a self) -> &'a T {
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match *self {
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Some(ref x) => x,
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None => fail!("called `Option::get_ref()` on a `None` value"),
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}
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}
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/// Gets a mutable reference to the value inside an option.
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///
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/// # Failure
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///
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/// Fails if the value equals `None`
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///
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/// # Safety note
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///
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/// In general, because this function may fail, its use is discouraged
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/// (calling `get` on `None` is akin to dereferencing a null pointer).
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/// Instead, prefer to use pattern matching and handle the `None`
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/// case explicitly.
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#[inline]
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pub fn get_mut_ref<'a>(&'a mut self) -> &'a mut T {
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match *self {
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Some(ref mut x) => x,
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None => fail!("called `Option::get_mut_ref()` on a `None` value"),
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}
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}
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}
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impl<T: Default> Option<T> {
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/// Returns the contained value or default (for this type)
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#[inline]
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pub fn unwrap_or_default(self) -> T {
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match self {
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Some(x) => x,
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None => Default::default()
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}
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}
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}
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/////////////////////////////////////////////////////////////////////////////
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// Trait implementations
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/////////////////////////////////////////////////////////////////////////////
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impl<T> Default for Option<T> {
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#[inline]
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fn default() -> Option<T> { None }
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}
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/////////////////////////////////////////////////////////////////////////////
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// The Option Iterator
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/////////////////////////////////////////////////////////////////////////////
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/// An iterator that yields either one or zero elements
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#[deriving(Clone)]
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pub struct Item<A> {
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priv opt: Option<A>
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}
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impl<A> Iterator<A> for Item<A> {
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#[inline]
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fn next(&mut self) -> Option<A> {
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self.opt.take()
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}
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#[inline]
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fn size_hint(&self) -> (uint, Option<uint>) {
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match self.opt {
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Some(_) => (1, Some(1)),
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None => (0, Some(0)),
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}
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}
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}
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impl<A> DoubleEndedIterator<A> for Item<A> {
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#[inline]
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fn next_back(&mut self) -> Option<A> {
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self.opt.take()
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}
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}
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impl<A> ExactSize<A> for Item<A> {}
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/////////////////////////////////////////////////////////////////////////////
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// Free functions
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/////////////////////////////////////////////////////////////////////////////
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/// Takes each element in the `Iterator`: if it is `None`, no further
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/// elements are taken, and the `None` is returned. Should no `None` occur, a
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/// vector containing the values of each `Option` is returned.
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///
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/// Here is an example which increments every integer in a vector,
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/// checking for overflow:
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///
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/// fn inc_conditionally(x: uint) -> Option<uint> {
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/// if x == uint::MAX { return None; }
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/// else { return Some(x+1u); }
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/// }
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/// let v = [1u, 2, 3];
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/// let res = collect(v.iter().map(|&x| inc_conditionally(x)));
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/// assert!(res == Some(~[2u, 3, 4]));
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#[inline]
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pub fn collect<T, Iter: Iterator<Option<T>>, V: FromIterator<T>>(iter: Iter) -> Option<V> {
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// FIXME(#11084): This should be twice as fast once this bug is closed.
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let mut iter = iter.scan(false, |state, x| {
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match x {
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Some(x) => Some(x),
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None => {
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*state = true;
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None
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}
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}
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});
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let v: V = FromIterator::from_iterator(&mut iter);
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if iter.state {
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None
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} else {
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Some(v)
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}
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}
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/////////////////////////////////////////////////////////////////////////////
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// Tests
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/////////////////////////////////////////////////////////////////////////////
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#[cfg(test)]
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mod tests {
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use super::*;
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use prelude::*;
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use iter::range;
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use str::StrSlice;
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use kinds::marker;
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use vec::ImmutableVector;
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#[test]
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fn test_get_ptr() {
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unsafe {
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let x = ~0;
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let addr_x: *int = ::cast::transmute(&*x);
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let opt = Some(x);
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let y = opt.unwrap();
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let addr_y: *int = ::cast::transmute(&*y);
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assert_eq!(addr_x, addr_y);
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}
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}
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#[test]
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fn test_get_str() {
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let x = ~"test";
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let addr_x = x.as_ptr();
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let opt = Some(x);
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let y = opt.unwrap();
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let addr_y = y.as_ptr();
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assert_eq!(addr_x, addr_y);
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}
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#[test]
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fn test_get_resource() {
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use rc::Rc;
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use cell::RefCell;
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struct R {
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i: Rc<RefCell<int>>,
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}
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#[unsafe_destructor]
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impl ::ops::Drop for R {
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fn drop(&mut self) {
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let ii = self.i.deref();
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ii.set(ii.get() + 1);
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}
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}
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fn R(i: Rc<RefCell<int>>) -> R {
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R {
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i: i
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}
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}
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let i = Rc::new(RefCell::new(0));
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{
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let x = R(i.clone());
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let opt = Some(x);
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let _y = opt.unwrap();
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}
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assert_eq!(i.deref().get(), 1);
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}
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#[test]
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fn test_option_dance() {
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let x = Some(());
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let mut y = Some(5);
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let mut y2 = 0;
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for _x in x.iter() {
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y2 = y.take_unwrap();
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}
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assert_eq!(y2, 5);
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assert!(y.is_none());
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}
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#[test] #[should_fail]
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fn test_option_too_much_dance() {
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let mut y = Some(marker::NoPod);
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let _y2 = y.take_unwrap();
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let _y3 = y.take_unwrap();
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}
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#[test]
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fn test_and() {
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let x: Option<int> = Some(1);
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assert_eq!(x.and(Some(2)), Some(2));
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assert_eq!(x.and(None::<int>), None);
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let x: Option<int> = None;
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assert_eq!(x.and(Some(2)), None);
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assert_eq!(x.and(None::<int>), None);
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}
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#[test]
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fn test_and_then() {
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let x: Option<int> = Some(1);
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assert_eq!(x.and_then(|x| Some(x + 1)), Some(2));
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assert_eq!(x.and_then(|_| None::<int>), None);
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let x: Option<int> = None;
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assert_eq!(x.and_then(|x| Some(x + 1)), None);
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assert_eq!(x.and_then(|_| None::<int>), None);
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}
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#[test]
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fn test_or() {
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let x: Option<int> = Some(1);
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assert_eq!(x.or(Some(2)), Some(1));
|
|
assert_eq!(x.or(None), Some(1));
|
|
|
|
let x: Option<int> = None;
|
|
assert_eq!(x.or(Some(2)), Some(2));
|
|
assert_eq!(x.or(None), None);
|
|
}
|
|
|
|
#[test]
|
|
fn test_or_else() {
|
|
let x: Option<int> = Some(1);
|
|
assert_eq!(x.or_else(|| Some(2)), Some(1));
|
|
assert_eq!(x.or_else(|| None), Some(1));
|
|
|
|
let x: Option<int> = None;
|
|
assert_eq!(x.or_else(|| Some(2)), Some(2));
|
|
assert_eq!(x.or_else(|| None), None);
|
|
}
|
|
|
|
#[test]
|
|
fn test_option_while_some() {
|
|
let mut i = 0;
|
|
Some(10).while_some(|j| {
|
|
i += 1;
|
|
if j > 0 {
|
|
Some(j-1)
|
|
} else {
|
|
None
|
|
}
|
|
});
|
|
assert_eq!(i, 11);
|
|
}
|
|
|
|
#[test]
|
|
fn test_unwrap() {
|
|
assert_eq!(Some(1).unwrap(), 1);
|
|
assert_eq!(Some(~"hello").unwrap(), ~"hello");
|
|
}
|
|
|
|
#[test]
|
|
#[should_fail]
|
|
fn test_unwrap_fail1() {
|
|
let x: Option<int> = None;
|
|
x.unwrap();
|
|
}
|
|
|
|
#[test]
|
|
#[should_fail]
|
|
fn test_unwrap_fail2() {
|
|
let x: Option<~str> = None;
|
|
x.unwrap();
|
|
}
|
|
|
|
#[test]
|
|
fn test_unwrap_or() {
|
|
let x: Option<int> = Some(1);
|
|
assert_eq!(x.unwrap_or(2), 1);
|
|
|
|
let x: Option<int> = None;
|
|
assert_eq!(x.unwrap_or(2), 2);
|
|
}
|
|
|
|
#[test]
|
|
fn test_unwrap_or_else() {
|
|
let x: Option<int> = Some(1);
|
|
assert_eq!(x.unwrap_or_else(|| 2), 1);
|
|
|
|
let x: Option<int> = None;
|
|
assert_eq!(x.unwrap_or_else(|| 2), 2);
|
|
}
|
|
|
|
#[test]
|
|
fn test_filtered() {
|
|
let some_stuff = Some(42);
|
|
let modified_stuff = some_stuff.filtered(|&x| {x < 10});
|
|
assert_eq!(some_stuff.unwrap(), 42);
|
|
assert!(modified_stuff.is_none());
|
|
}
|
|
|
|
#[test]
|
|
fn test_iter() {
|
|
let val = 5;
|
|
|
|
let x = Some(val);
|
|
let mut it = x.iter();
|
|
|
|
assert_eq!(it.size_hint(), (1, Some(1)));
|
|
assert_eq!(it.next(), Some(&val));
|
|
assert_eq!(it.size_hint(), (0, Some(0)));
|
|
assert!(it.next().is_none());
|
|
}
|
|
|
|
#[test]
|
|
fn test_mut_iter() {
|
|
let val = 5;
|
|
let new_val = 11;
|
|
|
|
let mut x = Some(val);
|
|
{
|
|
let mut it = x.mut_iter();
|
|
|
|
assert_eq!(it.size_hint(), (1, Some(1)));
|
|
|
|
match it.next() {
|
|
Some(interior) => {
|
|
assert_eq!(*interior, val);
|
|
*interior = new_val;
|
|
}
|
|
None => assert!(false),
|
|
}
|
|
|
|
assert_eq!(it.size_hint(), (0, Some(0)));
|
|
assert!(it.next().is_none());
|
|
}
|
|
assert_eq!(x, Some(new_val));
|
|
}
|
|
|
|
#[test]
|
|
fn test_ord() {
|
|
let small = Some(1.0);
|
|
let big = Some(5.0);
|
|
let nan = Some(0.0/0.0);
|
|
assert!(!(nan < big));
|
|
assert!(!(nan > big));
|
|
assert!(small < big);
|
|
assert!(None < big);
|
|
assert!(big > None);
|
|
}
|
|
|
|
#[test]
|
|
fn test_mutate() {
|
|
let mut x = Some(3i);
|
|
assert!(x.mutate(|i| i+1));
|
|
assert_eq!(x, Some(4i));
|
|
assert!(x.mutate_or_set(0, |i| i+1));
|
|
assert_eq!(x, Some(5i));
|
|
x = None;
|
|
assert!(!x.mutate(|i| i+1));
|
|
assert_eq!(x, None);
|
|
assert!(!x.mutate_or_set(0i, |i| i+1));
|
|
assert_eq!(x, Some(0i));
|
|
}
|
|
|
|
#[test]
|
|
fn test_collect() {
|
|
let v: Option<~[int]> = collect(range(0, 0)
|
|
.map(|_| Some(0)));
|
|
assert_eq!(v, Some(~[]));
|
|
|
|
let v: Option<~[int]> = collect(range(0, 3)
|
|
.map(|x| Some(x)));
|
|
assert_eq!(v, Some(~[0, 1, 2]));
|
|
|
|
let v: Option<~[int]> = collect(range(0, 3)
|
|
.map(|x| if x > 1 { None } else { Some(x) }));
|
|
assert_eq!(v, None);
|
|
|
|
// test that it does not take more elements than it needs
|
|
let functions = [|| Some(()), || None, || fail!()];
|
|
|
|
let v: Option<~[()]> = collect(functions.iter().map(|f| (*f)()));
|
|
|
|
assert_eq!(v, None);
|
|
}
|
|
}
|