1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 //! Type [`Option`] represents an optional value: every [`Option`]
14 //! is either [`Some`] and contains a value, or [`None`], and
15 //! does not. [`Option`] types are very common in Rust code, as
16 //! they have a number of uses:
19 //! * Return values for functions that are not defined
20 //! over their entire input range (partial functions)
21 //! * Return value for otherwise reporting simple errors, where `None` is
23 //! * Optional struct fields
24 //! * Struct fields that can be loaned or "taken"
25 //! * Optional function arguments
26 //! * Nullable pointers
27 //! * Swapping things out of difficult situations
29 //! [`Option`]s are commonly paired with pattern matching to query the presence
30 //! of a value and take action, always accounting for the [`None`] case.
33 //! fn divide(numerator: f64, denominator: f64) -> Option<f64> {
34 //! if denominator == 0.0 {
37 //! Some(numerator / denominator)
41 //! // The return value of the function is an option
42 //! let result = divide(2.0, 3.0);
44 //! // Pattern match to retrieve the value
46 //! // The division was valid
47 //! Some(x) => println!("Result: {}", x),
48 //! // The division was invalid
49 //! None => println!("Cannot divide by 0"),
54 // FIXME: Show how `Option` is used in practice, with lots of methods
56 //! # Options and pointers ("nullable" pointers)
58 //! Rust's pointer types must always point to a valid location; there are
59 //! no "null" pointers. Instead, Rust has *optional* pointers, like
60 //! the optional owned box, [`Option`]`<`[`Box<T>`]`>`.
62 //! The following example uses [`Option`] to create an optional box of
63 //! [`i32`]. Notice that in order to use the inner [`i32`] value first, the
64 //! `check_optional` function needs to use pattern matching to
65 //! determine whether the box has a value (i.e. it is [`Some(...)`][`Some`]) or
69 //! let optional: Option<Box<i32>> = None;
70 //! check_optional(&optional);
72 //! let optional: Option<Box<i32>> = Some(Box::new(9000));
73 //! check_optional(&optional);
75 //! fn check_optional(optional: &Option<Box<i32>>) {
77 //! Some(ref p) => println!("has value {}", p),
78 //! None => println!("has no value"),
83 //! This usage of [`Option`] to create safe nullable pointers is so
84 //! common that Rust does special optimizations to make the
85 //! representation of [`Option`]`<`[`Box<T>`]`>` a single pointer. Optional pointers
86 //! in Rust are stored as efficiently as any other pointer type.
90 //! Basic pattern matching on [`Option`]:
93 //! let msg = Some("howdy");
95 //! // Take a reference to the contained string
96 //! if let Some(ref m) = msg {
97 //! println!("{}", *m);
100 //! // Remove the contained string, destroying the Option
101 //! let unwrapped_msg = msg.unwrap_or("default message");
104 //! Initialize a result to [`None`] before a loop:
107 //! enum Kingdom { Plant(u32, &'static str), Animal(u32, &'static str) }
109 //! // A list of data to search through.
110 //! let all_the_big_things = [
111 //! Kingdom::Plant(250, "redwood"),
112 //! Kingdom::Plant(230, "noble fir"),
113 //! Kingdom::Plant(229, "sugar pine"),
114 //! Kingdom::Animal(25, "blue whale"),
115 //! Kingdom::Animal(19, "fin whale"),
116 //! Kingdom::Animal(15, "north pacific right whale"),
119 //! // We're going to search for the name of the biggest animal,
120 //! // but to start with we've just got `None`.
121 //! let mut name_of_biggest_animal = None;
122 //! let mut size_of_biggest_animal = 0;
123 //! for big_thing in &all_the_big_things {
124 //! match *big_thing {
125 //! Kingdom::Animal(size, name) if size > size_of_biggest_animal => {
126 //! // Now we've found the name of some big animal
127 //! size_of_biggest_animal = size;
128 //! name_of_biggest_animal = Some(name);
130 //! Kingdom::Animal(..) | Kingdom::Plant(..) => ()
134 //! match name_of_biggest_animal {
135 //! Some(name) => println!("the biggest animal is {}", name),
136 //! None => println!("there are no animals :("),
140 //! [`Option`]: enum.Option.html
141 //! [`Some`]: enum.Option.html#variant.Some
142 //! [`None`]: enum.Option.html#variant.None
143 //! [`Box<T>`]: ../../std/boxed/struct.Box.html
144 //! [`i32`]: ../../std/primitive.i32.html
146 #![stable(feature = "rust1", since = "1.0.0")]
148 use iter::{FromIterator, FusedIterator, TrustedLen};
151 // Note that this is not a lang item per se, but it has a hidden dependency on
152 // `Iterator`, which is one. The compiler assumes that the `next` method of
153 // `Iterator` is an enumeration with one type parameter and two variants,
154 // which basically means it must be `Option`.
156 /// The `Option` type. See [the module level documentation](index.html) for more.
157 #[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)]
158 #[stable(feature = "rust1", since = "1.0.0")]
161 #[stable(feature = "rust1", since = "1.0.0")]
164 #[stable(feature = "rust1", since = "1.0.0")]
165 Some(#[stable(feature = "rust1", since = "1.0.0")] T),
168 /////////////////////////////////////////////////////////////////////////////
169 // Type implementation
170 /////////////////////////////////////////////////////////////////////////////
173 /////////////////////////////////////////////////////////////////////////
174 // Querying the contained values
175 /////////////////////////////////////////////////////////////////////////
177 /// Returns `true` if the option is a `Some` value.
182 /// let x: Option<u32> = Some(2);
183 /// assert_eq!(x.is_some(), true);
185 /// let x: Option<u32> = None;
186 /// assert_eq!(x.is_some(), false);
189 #[stable(feature = "rust1", since = "1.0.0")]
190 pub fn is_some(&self) -> bool {
197 /// Returns `true` if the option is a `None` value.
202 /// let x: Option<u32> = Some(2);
203 /// assert_eq!(x.is_none(), false);
205 /// let x: Option<u32> = None;
206 /// assert_eq!(x.is_none(), true);
209 #[stable(feature = "rust1", since = "1.0.0")]
210 pub fn is_none(&self) -> bool {
214 /////////////////////////////////////////////////////////////////////////
215 // Adapter for working with references
216 /////////////////////////////////////////////////////////////////////////
218 /// Converts from `Option<T>` to `Option<&T>`.
222 /// Convert an `Option<`[`String`]`>` into an `Option<`[`usize`]`>`, preserving the original.
223 /// The [`map`] method takes the `self` argument by value, consuming the original,
224 /// so this technique uses `as_ref` to first take an `Option` to a reference
225 /// to the value inside the original.
227 /// [`map`]: enum.Option.html#method.map
228 /// [`String`]: ../../std/string/struct.String.html
229 /// [`usize`]: ../../std/primitive.usize.html
232 /// let num_as_str: Option<String> = Some("10".to_string());
233 /// // First, cast `Option<String>` to `Option<&String>` with `as_ref`,
234 /// // then consume *that* with `map`, leaving `num_as_str` on the stack.
235 /// let num_as_int: Option<usize> = num_as_str.as_ref().map(|n| n.len());
236 /// println!("still can print num_as_str: {:?}", num_as_str);
239 #[stable(feature = "rust1", since = "1.0.0")]
240 pub fn as_ref(&self) -> Option<&T> {
242 Some(ref x) => Some(x),
247 /// Converts from `Option<T>` to `Option<&mut T>`.
252 /// let mut x = Some(2);
253 /// match x.as_mut() {
254 /// Some(v) => *v = 42,
257 /// assert_eq!(x, Some(42));
260 #[stable(feature = "rust1", since = "1.0.0")]
261 pub fn as_mut(&mut self) -> Option<&mut T> {
263 Some(ref mut x) => Some(x),
268 /////////////////////////////////////////////////////////////////////////
269 // Getting to contained values
270 /////////////////////////////////////////////////////////////////////////
272 /// Unwraps an option, yielding the content of a `Some`.
276 /// Panics if the value is a [`None`] with a custom panic message provided by
279 /// [`None`]: #variant.None
284 /// let x = Some("value");
285 /// assert_eq!(x.expect("the world is ending"), "value");
288 /// ```{.should_panic}
289 /// let x: Option<&str> = None;
290 /// x.expect("the world is ending"); // panics with `the world is ending`
293 #[stable(feature = "rust1", since = "1.0.0")]
294 pub fn expect(self, msg: &str) -> T {
297 None => expect_failed(msg),
301 /// Moves the value `v` out of the `Option<T>` if it is `Some(v)`.
303 /// In general, because this function may panic, its use is discouraged.
304 /// Instead, prefer to use pattern matching and handle the `None`
309 /// Panics if the self value equals [`None`].
311 /// [`None`]: #variant.None
316 /// let x = Some("air");
317 /// assert_eq!(x.unwrap(), "air");
320 /// ```{.should_panic}
321 /// let x: Option<&str> = None;
322 /// assert_eq!(x.unwrap(), "air"); // fails
325 #[stable(feature = "rust1", since = "1.0.0")]
326 pub fn unwrap(self) -> T {
329 None => panic!("called `Option::unwrap()` on a `None` value"),
333 /// Returns the contained value or a default.
338 /// assert_eq!(Some("car").unwrap_or("bike"), "car");
339 /// assert_eq!(None.unwrap_or("bike"), "bike");
342 #[stable(feature = "rust1", since = "1.0.0")]
343 pub fn unwrap_or(self, def: T) -> T {
350 /// Returns the contained value or computes it from a closure.
356 /// assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4);
357 /// assert_eq!(None.unwrap_or_else(|| 2 * k), 20);
360 #[stable(feature = "rust1", since = "1.0.0")]
361 pub fn unwrap_or_else<F: FnOnce() -> T>(self, f: F) -> T {
368 /////////////////////////////////////////////////////////////////////////
369 // Transforming contained values
370 /////////////////////////////////////////////////////////////////////////
372 /// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value.
376 /// Convert an `Option<`[`String`]`>` into an `Option<`[`usize`]`>`, consuming the original:
378 /// [`String`]: ../../std/string/struct.String.html
379 /// [`usize`]: ../../std/primitive.usize.html
382 /// let maybe_some_string = Some(String::from("Hello, World!"));
383 /// // `Option::map` takes self *by value*, consuming `maybe_some_string`
384 /// let maybe_some_len = maybe_some_string.map(|s| s.len());
386 /// assert_eq!(maybe_some_len, Some(13));
389 #[stable(feature = "rust1", since = "1.0.0")]
390 pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Option<U> {
392 Some(x) => Some(f(x)),
397 /// Applies a function to the contained value (if any),
398 /// or returns a `default` (if not).
403 /// let x = Some("foo");
404 /// assert_eq!(x.map_or(42, |v| v.len()), 3);
406 /// let x: Option<&str> = None;
407 /// assert_eq!(x.map_or(42, |v| v.len()), 42);
410 #[stable(feature = "rust1", since = "1.0.0")]
411 pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U {
418 /// Applies a function to the contained value (if any),
419 /// or computes a `default` (if not).
426 /// let x = Some("foo");
427 /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3);
429 /// let x: Option<&str> = None;
430 /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42);
433 #[stable(feature = "rust1", since = "1.0.0")]
434 pub fn map_or_else<U, D: FnOnce() -> U, F: FnOnce(T) -> U>(self, default: D, f: F) -> U {
441 /// Transforms the `Option<T>` into a [`Result<T, E>`], mapping `Some(v)` to
442 /// [`Ok(v)`] and `None` to [`Err(err)`][Err].
444 /// [`Result<T, E>`]: ../../std/result/enum.Result.html
445 /// [`Ok(v)`]: ../../std/result/enum.Result.html#variant.Ok
446 /// [Err]: ../../std/result/enum.Result.html#variant.Err
451 /// let x = Some("foo");
452 /// assert_eq!(x.ok_or(0), Ok("foo"));
454 /// let x: Option<&str> = None;
455 /// assert_eq!(x.ok_or(0), Err(0));
458 #[stable(feature = "rust1", since = "1.0.0")]
459 pub fn ok_or<E>(self, err: E) -> Result<T, E> {
466 /// Transforms the `Option<T>` into a [`Result<T, E>`], mapping `Some(v)` to
467 /// [`Ok(v)`] and `None` to [`Err(err())`][Err].
469 /// [`Result<T, E>`]: ../../std/result/enum.Result.html
470 /// [`Ok(v)`]: ../../std/result/enum.Result.html#variant.Ok
471 /// [Err]: ../../std/result/enum.Result.html#variant.Err
476 /// let x = Some("foo");
477 /// assert_eq!(x.ok_or_else(|| 0), Ok("foo"));
479 /// let x: Option<&str> = None;
480 /// assert_eq!(x.ok_or_else(|| 0), Err(0));
483 #[stable(feature = "rust1", since = "1.0.0")]
484 pub fn ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E> {
491 /////////////////////////////////////////////////////////////////////////
492 // Iterator constructors
493 /////////////////////////////////////////////////////////////////////////
495 /// Returns an iterator over the possibly contained value.
501 /// assert_eq!(x.iter().next(), Some(&4));
503 /// let x: Option<u32> = None;
504 /// assert_eq!(x.iter().next(), None);
507 #[stable(feature = "rust1", since = "1.0.0")]
508 pub fn iter(&self) -> Iter<T> {
509 Iter { inner: Item { opt: self.as_ref() } }
512 /// Returns a mutable iterator over the possibly contained value.
517 /// let mut x = Some(4);
518 /// match x.iter_mut().next() {
519 /// Some(v) => *v = 42,
522 /// assert_eq!(x, Some(42));
524 /// let mut x: Option<u32> = None;
525 /// assert_eq!(x.iter_mut().next(), None);
528 #[stable(feature = "rust1", since = "1.0.0")]
529 pub fn iter_mut(&mut self) -> IterMut<T> {
530 IterMut { inner: Item { opt: self.as_mut() } }
533 /////////////////////////////////////////////////////////////////////////
534 // Boolean operations on the values, eager and lazy
535 /////////////////////////////////////////////////////////////////////////
537 /// Returns `None` if the option is `None`, otherwise returns `optb`.
543 /// let y: Option<&str> = None;
544 /// assert_eq!(x.and(y), None);
546 /// let x: Option<u32> = None;
547 /// let y = Some("foo");
548 /// assert_eq!(x.and(y), None);
551 /// let y = Some("foo");
552 /// assert_eq!(x.and(y), Some("foo"));
554 /// let x: Option<u32> = None;
555 /// let y: Option<&str> = None;
556 /// assert_eq!(x.and(y), None);
559 #[stable(feature = "rust1", since = "1.0.0")]
560 pub fn and<U>(self, optb: Option<U>) -> Option<U> {
567 /// Returns `None` if the option is `None`, otherwise calls `f` with the
568 /// wrapped value and returns the result.
570 /// Some languages call this operation flatmap.
575 /// fn sq(x: u32) -> Option<u32> { Some(x * x) }
576 /// fn nope(_: u32) -> Option<u32> { None }
578 /// assert_eq!(Some(2).and_then(sq).and_then(sq), Some(16));
579 /// assert_eq!(Some(2).and_then(sq).and_then(nope), None);
580 /// assert_eq!(Some(2).and_then(nope).and_then(sq), None);
581 /// assert_eq!(None.and_then(sq).and_then(sq), None);
584 #[stable(feature = "rust1", since = "1.0.0")]
585 pub fn and_then<U, F: FnOnce(T) -> Option<U>>(self, f: F) -> Option<U> {
592 /// Returns the option if it contains a value, otherwise returns `optb`.
599 /// assert_eq!(x.or(y), Some(2));
602 /// let y = Some(100);
603 /// assert_eq!(x.or(y), Some(100));
606 /// let y = Some(100);
607 /// assert_eq!(x.or(y), Some(2));
609 /// let x: Option<u32> = None;
611 /// assert_eq!(x.or(y), None);
614 #[stable(feature = "rust1", since = "1.0.0")]
615 pub fn or(self, optb: Option<T>) -> Option<T> {
622 /// Returns the option if it contains a value, otherwise calls `f` and
623 /// returns the result.
628 /// fn nobody() -> Option<&'static str> { None }
629 /// fn vikings() -> Option<&'static str> { Some("vikings") }
631 /// assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians"));
632 /// assert_eq!(None.or_else(vikings), Some("vikings"));
633 /// assert_eq!(None.or_else(nobody), None);
636 #[stable(feature = "rust1", since = "1.0.0")]
637 pub fn or_else<F: FnOnce() -> Option<T>>(self, f: F) -> Option<T> {
644 /////////////////////////////////////////////////////////////////////////
645 // Entry-like operations to insert if None and return a reference
646 /////////////////////////////////////////////////////////////////////////
648 /// Inserts `v` into the option if it is `None`, then
649 /// returns a mutable reference to the contained value.
654 /// #![feature(option_entry)]
656 /// let mut x = None;
659 /// let y: &mut u32 = x.get_or_insert(5);
660 /// assert_eq!(y, &5);
665 /// assert_eq!(x, Some(7));
668 #[unstable(feature = "option_entry", issue = "39288")]
669 pub fn get_or_insert(&mut self, v: T) -> &mut T {
671 None => *self = Some(v),
676 Some(ref mut v) => v,
681 /// Inserts a value computed from `f` into the option if it is `None`, then
682 /// returns a mutable reference to the contained value.
687 /// #![feature(option_entry)]
689 /// let mut x = None;
692 /// let y: &mut u32 = x.get_or_insert_with(|| 5);
693 /// assert_eq!(y, &5);
698 /// assert_eq!(x, Some(7));
701 #[unstable(feature = "option_entry", issue = "39288")]
702 pub fn get_or_insert_with<F: FnOnce() -> T>(&mut self, f: F) -> &mut T {
704 None => *self = Some(f()),
709 Some(ref mut v) => v,
714 /////////////////////////////////////////////////////////////////////////
716 /////////////////////////////////////////////////////////////////////////
718 /// Takes the value out of the option, leaving a `None` in its place.
723 /// let mut x = Some(2);
725 /// assert_eq!(x, None);
727 /// let mut x: Option<u32> = None;
729 /// assert_eq!(x, None);
732 #[stable(feature = "rust1", since = "1.0.0")]
733 pub fn take(&mut self) -> Option<T> {
734 mem::replace(self, None)
738 impl<'a, T: Clone> Option<&'a T> {
739 /// Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the
746 /// let opt_x = Some(&x);
747 /// assert_eq!(opt_x, Some(&12));
748 /// let cloned = opt_x.cloned();
749 /// assert_eq!(cloned, Some(12));
751 #[stable(feature = "rust1", since = "1.0.0")]
752 pub fn cloned(self) -> Option<T> {
753 self.map(|t| t.clone())
757 impl<T: Default> Option<T> {
758 /// Returns the contained value or a default
760 /// Consumes the `self` argument then, if `Some`, returns the contained
761 /// value, otherwise if `None`, returns the default value for that
766 /// Convert a string to an integer, turning poorly-formed strings
767 /// into 0 (the default value for integers). `parse` converts
768 /// a string to any other type that implements `FromStr`, returning
772 /// let good_year_from_input = "1909";
773 /// let bad_year_from_input = "190blarg";
774 /// let good_year = good_year_from_input.parse().ok().unwrap_or_default();
775 /// let bad_year = bad_year_from_input.parse().ok().unwrap_or_default();
777 /// assert_eq!(1909, good_year);
778 /// assert_eq!(0, bad_year);
781 #[stable(feature = "rust1", since = "1.0.0")]
782 pub fn unwrap_or_default(self) -> T {
785 None => Default::default(),
790 // This is a separate function to reduce the code size of .expect() itself.
793 fn expect_failed(msg: &str) -> ! {
798 /////////////////////////////////////////////////////////////////////////////
799 // Trait implementations
800 /////////////////////////////////////////////////////////////////////////////
802 #[stable(feature = "rust1", since = "1.0.0")]
803 impl<T> Default for Option<T> {
806 fn default() -> Option<T> { None }
809 #[stable(feature = "rust1", since = "1.0.0")]
810 impl<T> IntoIterator for Option<T> {
812 type IntoIter = IntoIter<T>;
814 /// Returns a consuming iterator over the possibly contained value.
819 /// let x = Some("string");
820 /// let v: Vec<&str> = x.into_iter().collect();
821 /// assert_eq!(v, ["string"]);
824 /// let v: Vec<&str> = x.into_iter().collect();
825 /// assert!(v.is_empty());
828 fn into_iter(self) -> IntoIter<T> {
829 IntoIter { inner: Item { opt: self } }
833 #[stable(since = "1.4.0", feature = "option_iter")]
834 impl<'a, T> IntoIterator for &'a Option<T> {
836 type IntoIter = Iter<'a, T>;
838 fn into_iter(self) -> Iter<'a, T> {
843 #[stable(since = "1.4.0", feature = "option_iter")]
844 impl<'a, T> IntoIterator for &'a mut Option<T> {
845 type Item = &'a mut T;
846 type IntoIter = IterMut<'a, T>;
848 fn into_iter(mut self) -> IterMut<'a, T> {
853 #[stable(since = "1.12.0", feature = "option_from")]
854 impl<T> From<T> for Option<T> {
855 fn from(val: T) -> Option<T> {
860 /////////////////////////////////////////////////////////////////////////////
861 // The Option Iterators
862 /////////////////////////////////////////////////////////////////////////////
864 #[derive(Clone, Debug)]
869 impl<A> Iterator for Item<A> {
873 fn next(&mut self) -> Option<A> {
878 fn size_hint(&self) -> (usize, Option<usize>) {
880 Some(_) => (1, Some(1)),
881 None => (0, Some(0)),
886 impl<A> DoubleEndedIterator for Item<A> {
888 fn next_back(&mut self) -> Option<A> {
893 impl<A> ExactSizeIterator for Item<A> {}
894 impl<A> FusedIterator for Item<A> {}
895 unsafe impl<A> TrustedLen for Item<A> {}
897 /// An iterator over a reference to the [`Some`] variant of an [`Option`].
899 /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.
901 /// This `struct` is created by the [`Option::iter`] function.
903 /// [`Option`]: enum.Option.html
904 /// [`Some`]: enum.Option.html#variant.Some
905 /// [`Option::iter`]: enum.Option.html#method.iter
906 #[stable(feature = "rust1", since = "1.0.0")]
908 pub struct Iter<'a, A: 'a> { inner: Item<&'a A> }
910 #[stable(feature = "rust1", since = "1.0.0")]
911 impl<'a, A> Iterator for Iter<'a, A> {
915 fn next(&mut self) -> Option<&'a A> { self.inner.next() }
917 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
920 #[stable(feature = "rust1", since = "1.0.0")]
921 impl<'a, A> DoubleEndedIterator for Iter<'a, A> {
923 fn next_back(&mut self) -> Option<&'a A> { self.inner.next_back() }
926 #[stable(feature = "rust1", since = "1.0.0")]
927 impl<'a, A> ExactSizeIterator for Iter<'a, A> {}
929 #[unstable(feature = "fused", issue = "35602")]
930 impl<'a, A> FusedIterator for Iter<'a, A> {}
932 #[unstable(feature = "trusted_len", issue = "37572")]
933 unsafe impl<'a, A> TrustedLen for Iter<'a, A> {}
935 #[stable(feature = "rust1", since = "1.0.0")]
936 impl<'a, A> Clone for Iter<'a, A> {
937 fn clone(&self) -> Iter<'a, A> {
938 Iter { inner: self.inner.clone() }
942 /// An iterator over a mutable reference to the [`Some`] variant of an [`Option`].
944 /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.
946 /// This `struct` is created by the [`Option::iter_mut`] function.
948 /// [`Option`]: enum.Option.html
949 /// [`Some`]: enum.Option.html#variant.Some
950 /// [`Option::iter_mut`]: enum.Option.html#method.iter_mut
951 #[stable(feature = "rust1", since = "1.0.0")]
953 pub struct IterMut<'a, A: 'a> { inner: Item<&'a mut A> }
955 #[stable(feature = "rust1", since = "1.0.0")]
956 impl<'a, A> Iterator for IterMut<'a, A> {
957 type Item = &'a mut A;
960 fn next(&mut self) -> Option<&'a mut A> { self.inner.next() }
962 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
965 #[stable(feature = "rust1", since = "1.0.0")]
966 impl<'a, A> DoubleEndedIterator for IterMut<'a, A> {
968 fn next_back(&mut self) -> Option<&'a mut A> { self.inner.next_back() }
971 #[stable(feature = "rust1", since = "1.0.0")]
972 impl<'a, A> ExactSizeIterator for IterMut<'a, A> {}
974 #[unstable(feature = "fused", issue = "35602")]
975 impl<'a, A> FusedIterator for IterMut<'a, A> {}
976 #[unstable(feature = "trusted_len", issue = "37572")]
977 unsafe impl<'a, A> TrustedLen for IterMut<'a, A> {}
979 /// An iterator over the value in [`Some`] variant of an [`Option`].
981 /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.
983 /// This `struct` is created by the [`Option::into_iter`] function.
985 /// [`Option`]: enum.Option.html
986 /// [`Some`]: enum.Option.html#variant.Some
987 /// [`Option::into_iter`]: enum.Option.html#method.into_iter
988 #[derive(Clone, Debug)]
989 #[stable(feature = "rust1", since = "1.0.0")]
990 pub struct IntoIter<A> { inner: Item<A> }
992 #[stable(feature = "rust1", since = "1.0.0")]
993 impl<A> Iterator for IntoIter<A> {
997 fn next(&mut self) -> Option<A> { self.inner.next() }
999 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1002 #[stable(feature = "rust1", since = "1.0.0")]
1003 impl<A> DoubleEndedIterator for IntoIter<A> {
1005 fn next_back(&mut self) -> Option<A> { self.inner.next_back() }
1008 #[stable(feature = "rust1", since = "1.0.0")]
1009 impl<A> ExactSizeIterator for IntoIter<A> {}
1011 #[unstable(feature = "fused", issue = "35602")]
1012 impl<A> FusedIterator for IntoIter<A> {}
1014 #[unstable(feature = "trusted_len", issue = "37572")]
1015 unsafe impl<A> TrustedLen for IntoIter<A> {}
1017 /////////////////////////////////////////////////////////////////////////////
1019 /////////////////////////////////////////////////////////////////////////////
1021 #[stable(feature = "rust1", since = "1.0.0")]
1022 impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> {
1023 /// Takes each element in the `Iterator`: if it is `None`, no further
1024 /// elements are taken, and the `None` is returned. Should no `None` occur, a
1025 /// container with the values of each `Option` is returned.
1027 /// Here is an example which increments every integer in a vector,
1028 /// checking for overflow:
1033 /// let v = vec![1, 2];
1034 /// let res: Option<Vec<u16>> = v.iter().map(|&x: &u16|
1035 /// if x == u16::MAX { None }
1036 /// else { Some(x + 1) }
1038 /// assert!(res == Some(vec![2, 3]));
1041 fn from_iter<I: IntoIterator<Item=Option<A>>>(iter: I) -> Option<V> {
1042 // FIXME(#11084): This could be replaced with Iterator::scan when this
1043 // performance bug is closed.
1045 struct Adapter<Iter> {
1050 impl<T, Iter: Iterator<Item=Option<T>>> Iterator for Adapter<Iter> {
1054 fn next(&mut self) -> Option<T> {
1055 match self.iter.next() {
1056 Some(Some(value)) => Some(value),
1058 self.found_none = true;
1066 let mut adapter = Adapter { iter: iter.into_iter(), found_none: false };
1067 let v: V = FromIterator::from_iter(adapter.by_ref());
1069 if adapter.found_none {