| //! Optional values. |
| //! |
| //! Type [`Option`] represents an optional value: every [`Option`] |
| //! is either [`Some`] and contains a value, or [`None`], and |
| //! does not. [`Option`] types are very common in Rust code, as |
| //! they have a number of uses: |
| //! |
| //! * Initial values |
| //! * Return values for functions that are not defined |
| //! over their entire input range (partial functions) |
| //! * Return value for otherwise reporting simple errors, where `None` is |
| //! returned on error |
| //! * Optional struct fields |
| //! * Struct fields that can be loaned or "taken" |
| //! * Optional function arguments |
| //! * Nullable pointers |
| //! * Swapping things out of difficult situations |
| //! |
| //! [`Option`]s are commonly paired with pattern matching to query the presence |
| //! of a value and take action, always accounting for the [`None`] case. |
| //! |
| //! ``` |
| //! fn divide(numerator: f64, denominator: f64) -> Option<f64> { |
| //! if denominator == 0.0 { |
| //! None |
| //! } else { |
| //! Some(numerator / denominator) |
| //! } |
| //! } |
| //! |
| //! // The return value of the function is an option |
| //! let result = divide(2.0, 3.0); |
| //! |
| //! // Pattern match to retrieve the value |
| //! match result { |
| //! // The division was valid |
| //! Some(x) => println!("Result: {}", x), |
| //! // The division was invalid |
| //! None => println!("Cannot divide by 0"), |
| //! } |
| //! ``` |
| //! |
| // |
| // FIXME: Show how `Option` is used in practice, with lots of methods |
| // |
| //! # Options and pointers ("nullable" pointers) |
| //! |
| //! Rust's pointer types must always point to a valid location; there are |
| //! no "null" pointers. Instead, Rust has *optional* pointers, like |
| //! the optional owned box, [`Option`]`<`[`Box<T>`]`>`. |
| //! |
| //! The following example uses [`Option`] to create an optional box of |
| //! [`i32`]. Notice that in order to use the inner [`i32`] value first, the |
| //! `check_optional` function needs to use pattern matching to |
| //! determine whether the box has a value (i.e., it is [`Some(...)`][`Some`]) or |
| //! not ([`None`]). |
| //! |
| //! ``` |
| //! let optional = None; |
| //! check_optional(optional); |
| //! |
| //! let optional = Some(Box::new(9000)); |
| //! check_optional(optional); |
| //! |
| //! fn check_optional(optional: Option<Box<i32>>) { |
| //! match optional { |
| //! Some(ref p) => println!("has value {}", p), |
| //! None => println!("has no value"), |
| //! } |
| //! } |
| //! ``` |
| //! |
| //! This usage of [`Option`] to create safe nullable pointers is so |
| //! common that Rust does special optimizations to make the |
| //! representation of [`Option`]`<`[`Box<T>`]`>` a single pointer. Optional pointers |
| //! in Rust are stored as efficiently as any other pointer type. |
| //! |
| //! # Examples |
| //! |
| //! Basic pattern matching on [`Option`]: |
| //! |
| //! ``` |
| //! let msg = Some("howdy"); |
| //! |
| //! // Take a reference to the contained string |
| //! if let Some(ref m) = msg { |
| //! println!("{}", *m); |
| //! } |
| //! |
| //! // Remove the contained string, destroying the Option |
| //! let unwrapped_msg = msg.unwrap_or("default message"); |
| //! ``` |
| //! |
| //! Initialize a result to [`None`] before a loop: |
| //! |
| //! ``` |
| //! enum Kingdom { Plant(u32, &'static str), Animal(u32, &'static str) } |
| //! |
| //! // A list of data to search through. |
| //! let all_the_big_things = [ |
| //! Kingdom::Plant(250, "redwood"), |
| //! Kingdom::Plant(230, "noble fir"), |
| //! Kingdom::Plant(229, "sugar pine"), |
| //! Kingdom::Animal(25, "blue whale"), |
| //! Kingdom::Animal(19, "fin whale"), |
| //! Kingdom::Animal(15, "north pacific right whale"), |
| //! ]; |
| //! |
| //! // We're going to search for the name of the biggest animal, |
| //! // but to start with we've just got `None`. |
| //! let mut name_of_biggest_animal = None; |
| //! let mut size_of_biggest_animal = 0; |
| //! for big_thing in &all_the_big_things { |
| //! match *big_thing { |
| //! Kingdom::Animal(size, name) if size > size_of_biggest_animal => { |
| //! // Now we've found the name of some big animal |
| //! size_of_biggest_animal = size; |
| //! name_of_biggest_animal = Some(name); |
| //! } |
| //! Kingdom::Animal(..) | Kingdom::Plant(..) => () |
| //! } |
| //! } |
| //! |
| //! match name_of_biggest_animal { |
| //! Some(name) => println!("the biggest animal is {}", name), |
| //! None => println!("there are no animals :("), |
| //! } |
| //! ``` |
| //! |
| //! [`Option`]: enum.Option.html |
| //! [`Some`]: enum.Option.html#variant.Some |
| //! [`None`]: enum.Option.html#variant.None |
| //! [`Box<T>`]: ../../std/boxed/struct.Box.html |
| //! [`i32`]: ../../std/primitive.i32.html |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| use crate::iter::{FromIterator, FusedIterator, TrustedLen}; |
| use crate::{convert, hint, mem, ops::{self, Deref}}; |
| use crate::pin::Pin; |
| |
| // Note that this is not a lang item per se, but it has a hidden dependency on |
| // `Iterator`, which is one. The compiler assumes that the `next` method of |
| // `Iterator` is an enumeration with one type parameter and two variants, |
| // which basically means it must be `Option`. |
| |
| /// The `Option` type. See [the module level documentation](index.html) for more. |
| #[derive(Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub enum Option<T> { |
| /// No value |
| #[stable(feature = "rust1", since = "1.0.0")] |
| None, |
| /// Some value `T` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| Some(#[stable(feature = "rust1", since = "1.0.0")] T), |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // Type implementation |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| impl<T> Option<T> { |
| ///////////////////////////////////////////////////////////////////////// |
| // Querying the contained values |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Returns `true` if the option is a [`Some`] value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x: Option<u32> = Some(2); |
| /// assert_eq!(x.is_some(), true); |
| /// |
| /// let x: Option<u32> = None; |
| /// assert_eq!(x.is_some(), false); |
| /// ``` |
| /// |
| /// [`Some`]: #variant.Some |
| #[must_use] |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn is_some(&self) -> bool { |
| match *self { |
| Some(_) => true, |
| None => false, |
| } |
| } |
| |
| /// Returns `true` if the option is a [`None`] value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x: Option<u32> = Some(2); |
| /// assert_eq!(x.is_none(), false); |
| /// |
| /// let x: Option<u32> = None; |
| /// assert_eq!(x.is_none(), true); |
| /// ``` |
| /// |
| /// [`None`]: #variant.None |
| #[must_use] |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn is_none(&self) -> bool { |
| !self.is_some() |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Adapter for working with references |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Converts from `&Option<T>` to `Option<&T>`. |
| /// |
| /// # Examples |
| /// |
| /// Converts an `Option<`[`String`]`>` into an `Option<`[`usize`]`>`, preserving the original. |
| /// The [`map`] method takes the `self` argument by value, consuming the original, |
| /// so this technique uses `as_ref` to first take an `Option` to a reference |
| /// to the value inside the original. |
| /// |
| /// [`map`]: enum.Option.html#method.map |
| /// [`String`]: ../../std/string/struct.String.html |
| /// [`usize`]: ../../std/primitive.usize.html |
| /// |
| /// ``` |
| /// let text: Option<String> = Some("Hello, world!".to_string()); |
| /// // First, cast `Option<String>` to `Option<&String>` with `as_ref`, |
| /// // then consume *that* with `map`, leaving `text` on the stack. |
| /// let text_length: Option<usize> = text.as_ref().map(|s| s.len()); |
| /// println!("still can print text: {:?}", text); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn as_ref(&self) -> Option<&T> { |
| match *self { |
| Some(ref x) => Some(x), |
| None => None, |
| } |
| } |
| |
| /// Converts from `&mut Option<T>` to `Option<&mut T>`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = Some(2); |
| /// match x.as_mut() { |
| /// Some(v) => *v = 42, |
| /// None => {}, |
| /// } |
| /// assert_eq!(x, Some(42)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn as_mut(&mut self) -> Option<&mut T> { |
| match *self { |
| Some(ref mut x) => Some(x), |
| None => None, |
| } |
| } |
| |
| |
| /// Converts from `Pin<&Option<T>>` to `Option<Pin<&T>>` |
| #[inline] |
| #[stable(feature = "pin", since = "1.33.0")] |
| pub fn as_pin_ref<'a>(self: Pin<&'a Option<T>>) -> Option<Pin<&'a T>> { |
| unsafe { |
| Pin::get_ref(self).as_ref().map(|x| Pin::new_unchecked(x)) |
| } |
| } |
| |
| /// Converts from `Pin<&mut Option<T>>` to `Option<Pin<&mut T>>` |
| #[inline] |
| #[stable(feature = "pin", since = "1.33.0")] |
| pub fn as_pin_mut<'a>(self: Pin<&'a mut Option<T>>) -> Option<Pin<&'a mut T>> { |
| unsafe { |
| Pin::get_unchecked_mut(self).as_mut().map(|x| Pin::new_unchecked(x)) |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Getting to contained values |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Unwraps an option, yielding the content of a [`Some`]. |
| /// |
| /// # Panics |
| /// |
| /// Panics if the value is a [`None`] with a custom panic message provided by |
| /// `msg`. |
| /// |
| /// [`Some`]: #variant.Some |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("value"); |
| /// assert_eq!(x.expect("the world is ending"), "value"); |
| /// ``` |
| /// |
| /// ```{.should_panic} |
| /// let x: Option<&str> = None; |
| /// x.expect("the world is ending"); // panics with `the world is ending` |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn expect(self, msg: &str) -> T { |
| match self { |
| Some(val) => val, |
| None => expect_failed(msg), |
| } |
| } |
| |
| /// Moves the value `v` out of the `Option<T>` if it is [`Some(v)`]. |
| /// |
| /// In general, because this function may panic, its use is discouraged. |
| /// Instead, prefer to use pattern matching and handle the [`None`] |
| /// case explicitly. |
| /// |
| /// # Panics |
| /// |
| /// Panics if the self value equals [`None`]. |
| /// |
| /// [`Some(v)`]: #variant.Some |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("air"); |
| /// assert_eq!(x.unwrap(), "air"); |
| /// ``` |
| /// |
| /// ```{.should_panic} |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.unwrap(), "air"); // fails |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap(self) -> T { |
| match self { |
| Some(val) => val, |
| None => panic!("called `Option::unwrap()` on a `None` value"), |
| } |
| } |
| |
| /// Returns the contained value or a default. |
| /// |
| /// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing |
| /// the result of a function call, it is recommended to use [`unwrap_or_else`], |
| /// which is lazily evaluated. |
| /// |
| /// [`unwrap_or_else`]: #method.unwrap_or_else |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!(Some("car").unwrap_or("bike"), "car"); |
| /// assert_eq!(None.unwrap_or("bike"), "bike"); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap_or(self, def: T) -> T { |
| match self { |
| Some(x) => x, |
| None => def, |
| } |
| } |
| |
| /// Returns the contained value or computes it from a closure. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let k = 10; |
| /// assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4); |
| /// assert_eq!(None.unwrap_or_else(|| 2 * k), 20); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap_or_else<F: FnOnce() -> T>(self, f: F) -> T { |
| match self { |
| Some(x) => x, |
| None => f(), |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Transforming contained values |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value. |
| /// |
| /// # Examples |
| /// |
| /// Converts an `Option<`[`String`]`>` into an `Option<`[`usize`]`>`, consuming the original: |
| /// |
| /// [`String`]: ../../std/string/struct.String.html |
| /// [`usize`]: ../../std/primitive.usize.html |
| /// |
| /// ``` |
| /// let maybe_some_string = Some(String::from("Hello, World!")); |
| /// // `Option::map` takes self *by value*, consuming `maybe_some_string` |
| /// let maybe_some_len = maybe_some_string.map(|s| s.len()); |
| /// |
| /// assert_eq!(maybe_some_len, Some(13)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Option<U> { |
| match self { |
| Some(x) => Some(f(x)), |
| None => None, |
| } |
| } |
| |
| /// Applies a function to the contained value (if any), |
| /// or returns the provided default (if not). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("foo"); |
| /// assert_eq!(x.map_or(42, |v| v.len()), 3); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.map_or(42, |v| v.len()), 42); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U { |
| match self { |
| Some(t) => f(t), |
| None => default, |
| } |
| } |
| |
| /// Applies a function to the contained value (if any), |
| /// or computes a default (if not). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let k = 21; |
| /// |
| /// let x = Some("foo"); |
| /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn map_or_else<U, D: FnOnce() -> U, F: FnOnce(T) -> U>(self, default: D, f: F) -> U { |
| match self { |
| Some(t) => f(t), |
| None => default(), |
| } |
| } |
| |
| /// Transforms the `Option<T>` into a [`Result<T, E>`], mapping [`Some(v)`] to |
| /// [`Ok(v)`] and [`None`] to [`Err(err)`]. |
| /// |
| /// Arguments passed to `ok_or` are eagerly evaluated; if you are passing the |
| /// result of a function call, it is recommended to use [`ok_or_else`], which is |
| /// lazily evaluated. |
| /// |
| /// [`Result<T, E>`]: ../../std/result/enum.Result.html |
| /// [`Ok(v)`]: ../../std/result/enum.Result.html#variant.Ok |
| /// [`Err(err)`]: ../../std/result/enum.Result.html#variant.Err |
| /// [`None`]: #variant.None |
| /// [`Some(v)`]: #variant.Some |
| /// [`ok_or_else`]: #method.ok_or_else |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("foo"); |
| /// assert_eq!(x.ok_or(0), Ok("foo")); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.ok_or(0), Err(0)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn ok_or<E>(self, err: E) -> Result<T, E> { |
| match self { |
| Some(v) => Ok(v), |
| None => Err(err), |
| } |
| } |
| |
| /// Transforms the `Option<T>` into a [`Result<T, E>`], mapping [`Some(v)`] to |
| /// [`Ok(v)`] and [`None`] to [`Err(err())`]. |
| /// |
| /// [`Result<T, E>`]: ../../std/result/enum.Result.html |
| /// [`Ok(v)`]: ../../std/result/enum.Result.html#variant.Ok |
| /// [`Err(err())`]: ../../std/result/enum.Result.html#variant.Err |
| /// [`None`]: #variant.None |
| /// [`Some(v)`]: #variant.Some |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("foo"); |
| /// assert_eq!(x.ok_or_else(|| 0), Ok("foo")); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.ok_or_else(|| 0), Err(0)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E> { |
| match self { |
| Some(v) => Ok(v), |
| None => Err(err()), |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Iterator constructors |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Returns an iterator over the possibly contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some(4); |
| /// assert_eq!(x.iter().next(), Some(&4)); |
| /// |
| /// let x: Option<u32> = None; |
| /// assert_eq!(x.iter().next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn iter(&self) -> Iter<'_, T> { |
| Iter { inner: Item { opt: self.as_ref() } } |
| } |
| |
| /// Returns a mutable iterator over the possibly contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = Some(4); |
| /// match x.iter_mut().next() { |
| /// Some(v) => *v = 42, |
| /// None => {}, |
| /// } |
| /// assert_eq!(x, Some(42)); |
| /// |
| /// let mut x: Option<u32> = None; |
| /// assert_eq!(x.iter_mut().next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn iter_mut(&mut self) -> IterMut<'_, T> { |
| IterMut { inner: Item { opt: self.as_mut() } } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Boolean operations on the values, eager and lazy |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Returns [`None`] if the option is [`None`], otherwise returns `optb`. |
| /// |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some(2); |
| /// let y: Option<&str> = None; |
| /// assert_eq!(x.and(y), None); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y = Some("foo"); |
| /// assert_eq!(x.and(y), None); |
| /// |
| /// let x = Some(2); |
| /// let y = Some("foo"); |
| /// assert_eq!(x.and(y), Some("foo")); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y: Option<&str> = None; |
| /// assert_eq!(x.and(y), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn and<U>(self, optb: Option<U>) -> Option<U> { |
| match self { |
| Some(_) => optb, |
| None => None, |
| } |
| } |
| |
| /// Returns [`None`] if the option is [`None`], otherwise calls `f` with the |
| /// wrapped value and returns the result. |
| /// |
| /// Some languages call this operation flatmap. |
| /// |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// fn sq(x: u32) -> Option<u32> { Some(x * x) } |
| /// fn nope(_: u32) -> Option<u32> { None } |
| /// |
| /// assert_eq!(Some(2).and_then(sq).and_then(sq), Some(16)); |
| /// assert_eq!(Some(2).and_then(sq).and_then(nope), None); |
| /// assert_eq!(Some(2).and_then(nope).and_then(sq), None); |
| /// assert_eq!(None.and_then(sq).and_then(sq), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn and_then<U, F: FnOnce(T) -> Option<U>>(self, f: F) -> Option<U> { |
| match self { |
| Some(x) => f(x), |
| None => None, |
| } |
| } |
| |
| /// Returns `None` if the option is `None`, otherwise calls `predicate` |
| /// with the wrapped value and returns: |
| /// |
| /// - `Some(t)` if `predicate` returns `true` (where `t` is the wrapped |
| /// value), and |
| /// - `None` if `predicate` returns `false`. |
| /// |
| /// This function works similar to `Iterator::filter()`. You can imagine |
| /// the `Option<T>` being an iterator over one or zero elements. `filter()` |
| /// lets you decide which elements to keep. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// fn is_even(n: &i32) -> bool { |
| /// n % 2 == 0 |
| /// } |
| /// |
| /// assert_eq!(None.filter(is_even), None); |
| /// assert_eq!(Some(3).filter(is_even), None); |
| /// assert_eq!(Some(4).filter(is_even), Some(4)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "option_filter", since = "1.27.0")] |
| pub fn filter<P: FnOnce(&T) -> bool>(self, predicate: P) -> Self { |
| if let Some(x) = self { |
| if predicate(&x) { |
| return Some(x) |
| } |
| } |
| None |
| } |
| |
| /// Returns the option if it contains a value, otherwise returns `optb`. |
| /// |
| /// Arguments passed to `or` are eagerly evaluated; if you are passing the |
| /// result of a function call, it is recommended to use [`or_else`], which is |
| /// lazily evaluated. |
| /// |
| /// [`or_else`]: #method.or_else |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some(2); |
| /// let y = None; |
| /// assert_eq!(x.or(y), Some(2)); |
| /// |
| /// let x = None; |
| /// let y = Some(100); |
| /// assert_eq!(x.or(y), Some(100)); |
| /// |
| /// let x = Some(2); |
| /// let y = Some(100); |
| /// assert_eq!(x.or(y), Some(2)); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y = None; |
| /// assert_eq!(x.or(y), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn or(self, optb: Option<T>) -> Option<T> { |
| match self { |
| Some(_) => self, |
| None => optb, |
| } |
| } |
| |
| /// Returns the option if it contains a value, otherwise calls `f` and |
| /// returns the result. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// fn nobody() -> Option<&'static str> { None } |
| /// fn vikings() -> Option<&'static str> { Some("vikings") } |
| /// |
| /// assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians")); |
| /// assert_eq!(None.or_else(vikings), Some("vikings")); |
| /// assert_eq!(None.or_else(nobody), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn or_else<F: FnOnce() -> Option<T>>(self, f: F) -> Option<T> { |
| match self { |
| Some(_) => self, |
| None => f(), |
| } |
| } |
| |
| /// Returns [`Some`] if exactly one of `self`, `optb` is [`Some`], otherwise returns `None`. |
| /// |
| /// [`Some`]: #variant.Some |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some(2); |
| /// let y: Option<u32> = None; |
| /// assert_eq!(x.xor(y), Some(2)); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y = Some(2); |
| /// assert_eq!(x.xor(y), Some(2)); |
| /// |
| /// let x = Some(2); |
| /// let y = Some(2); |
| /// assert_eq!(x.xor(y), None); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y: Option<u32> = None; |
| /// assert_eq!(x.xor(y), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "option_xor", since = "1.37.0")] |
| pub fn xor(self, optb: Option<T>) -> Option<T> { |
| match (self, optb) { |
| (Some(a), None) => Some(a), |
| (None, Some(b)) => Some(b), |
| _ => None, |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Entry-like operations to insert if None and return a reference |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Inserts `v` into the option if it is [`None`], then |
| /// returns a mutable reference to the contained value. |
| /// |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = None; |
| /// |
| /// { |
| /// let y: &mut u32 = x.get_or_insert(5); |
| /// assert_eq!(y, &5); |
| /// |
| /// *y = 7; |
| /// } |
| /// |
| /// assert_eq!(x, Some(7)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "option_entry", since = "1.20.0")] |
| pub fn get_or_insert(&mut self, v: T) -> &mut T { |
| match *self { |
| None => *self = Some(v), |
| _ => (), |
| } |
| |
| match *self { |
| Some(ref mut v) => v, |
| None => unsafe { hint::unreachable_unchecked() }, |
| } |
| } |
| |
| /// Inserts a value computed from `f` into the option if it is [`None`], then |
| /// returns a mutable reference to the contained value. |
| /// |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = None; |
| /// |
| /// { |
| /// let y: &mut u32 = x.get_or_insert_with(|| 5); |
| /// assert_eq!(y, &5); |
| /// |
| /// *y = 7; |
| /// } |
| /// |
| /// assert_eq!(x, Some(7)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "option_entry", since = "1.20.0")] |
| pub fn get_or_insert_with<F: FnOnce() -> T>(&mut self, f: F) -> &mut T { |
| match *self { |
| None => *self = Some(f()), |
| _ => (), |
| } |
| |
| match *self { |
| Some(ref mut v) => v, |
| None => unsafe { hint::unreachable_unchecked() }, |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Misc |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Takes the value out of the option, leaving a [`None`] in its place. |
| /// |
| /// [`None`]: #variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = Some(2); |
| /// let y = x.take(); |
| /// assert_eq!(x, None); |
| /// assert_eq!(y, Some(2)); |
| /// |
| /// let mut x: Option<u32> = None; |
| /// let y = x.take(); |
| /// assert_eq!(x, None); |
| /// assert_eq!(y, None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn take(&mut self) -> Option<T> { |
| mem::replace(self, None) |
| } |
| |
| /// Replaces the actual value in the option by the value given in parameter, |
| /// returning the old value if present, |
| /// leaving a [`Some`] in its place without deinitializing either one. |
| /// |
| /// [`Some`]: #variant.Some |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = Some(2); |
| /// let old = x.replace(5); |
| /// assert_eq!(x, Some(5)); |
| /// assert_eq!(old, Some(2)); |
| /// |
| /// let mut x = None; |
| /// let old = x.replace(3); |
| /// assert_eq!(x, Some(3)); |
| /// assert_eq!(old, None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "option_replace", since = "1.31.0")] |
| pub fn replace(&mut self, value: T) -> Option<T> { |
| mem::replace(self, Some(value)) |
| } |
| } |
| |
| impl<T: Copy> Option<&T> { |
| /// Maps an `Option<&T>` to an `Option<T>` by copying the contents of the |
| /// option. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = 12; |
| /// let opt_x = Some(&x); |
| /// assert_eq!(opt_x, Some(&12)); |
| /// let copied = opt_x.copied(); |
| /// assert_eq!(copied, Some(12)); |
| /// ``` |
| #[stable(feature = "copied", since = "1.35.0")] |
| pub fn copied(self) -> Option<T> { |
| self.map(|&t| t) |
| } |
| } |
| |
| impl<T: Copy> Option<&mut T> { |
| /// Maps an `Option<&mut T>` to an `Option<T>` by copying the contents of the |
| /// option. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = 12; |
| /// let opt_x = Some(&mut x); |
| /// assert_eq!(opt_x, Some(&mut 12)); |
| /// let copied = opt_x.copied(); |
| /// assert_eq!(copied, Some(12)); |
| /// ``` |
| #[stable(feature = "copied", since = "1.35.0")] |
| pub fn copied(self) -> Option<T> { |
| self.map(|&mut t| t) |
| } |
| } |
| |
| impl<T: Clone> Option<&T> { |
| /// Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the |
| /// option. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = 12; |
| /// let opt_x = Some(&x); |
| /// assert_eq!(opt_x, Some(&12)); |
| /// let cloned = opt_x.cloned(); |
| /// assert_eq!(cloned, Some(12)); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn cloned(self) -> Option<T> { |
| self.map(|t| t.clone()) |
| } |
| } |
| |
| impl<T: Clone> Option<&mut T> { |
| /// Maps an `Option<&mut T>` to an `Option<T>` by cloning the contents of the |
| /// option. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = 12; |
| /// let opt_x = Some(&mut x); |
| /// assert_eq!(opt_x, Some(&mut 12)); |
| /// let cloned = opt_x.cloned(); |
| /// assert_eq!(cloned, Some(12)); |
| /// ``` |
| #[stable(since = "1.26.0", feature = "option_ref_mut_cloned")] |
| pub fn cloned(self) -> Option<T> { |
| self.map(|t| t.clone()) |
| } |
| } |
| |
| impl<T: Default> Option<T> { |
| /// Returns the contained value or a default |
| /// |
| /// Consumes the `self` argument then, if [`Some`], returns the contained |
| /// value, otherwise if [`None`], returns the [default value] for that |
| /// type. |
| /// |
| /// # Examples |
| /// |
| /// Converts a string to an integer, turning poorly-formed strings |
| /// into 0 (the default value for integers). [`parse`] converts |
| /// a string to any other type that implements [`FromStr`], returning |
| /// [`None`] on error. |
| /// |
| /// ``` |
| /// let good_year_from_input = "1909"; |
| /// let bad_year_from_input = "190blarg"; |
| /// let good_year = good_year_from_input.parse().ok().unwrap_or_default(); |
| /// let bad_year = bad_year_from_input.parse().ok().unwrap_or_default(); |
| /// |
| /// assert_eq!(1909, good_year); |
| /// assert_eq!(0, bad_year); |
| /// ``` |
| /// |
| /// [`Some`]: #variant.Some |
| /// [`None`]: #variant.None |
| /// [default value]: ../default/trait.Default.html#tymethod.default |
| /// [`parse`]: ../../std/primitive.str.html#method.parse |
| /// [`FromStr`]: ../../std/str/trait.FromStr.html |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap_or_default(self) -> T { |
| match self { |
| Some(x) => x, |
| None => Default::default(), |
| } |
| } |
| } |
| |
| #[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")] |
| impl<T: Deref> Option<T> { |
| /// Converts from `&Option<T>` to `Option<&T::Target>`. |
| /// |
| /// Leaves the original Option in-place, creating a new one with a reference |
| /// to the original one, additionally coercing the contents via `Deref`. |
| pub fn deref(&self) -> Option<&T::Target> { |
| self.as_ref().map(|t| t.deref()) |
| } |
| } |
| |
| impl<T, E> Option<Result<T, E>> { |
| /// Transposes an `Option` of a `Result` into a `Result` of an `Option`. |
| /// |
| /// `None` will be mapped to `Ok(None)`. |
| /// `Some(Ok(_))` and `Some(Err(_))` will be mapped to `Ok(Some(_))` and `Err(_)`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #[derive(Debug, Eq, PartialEq)] |
| /// struct SomeErr; |
| /// |
| /// let x: Result<Option<i32>, SomeErr> = Ok(Some(5)); |
| /// let y: Option<Result<i32, SomeErr>> = Some(Ok(5)); |
| /// assert_eq!(x, y.transpose()); |
| /// ``` |
| #[inline] |
| #[stable(feature = "transpose_result", since = "1.33.0")] |
| pub fn transpose(self) -> Result<Option<T>, E> { |
| match self { |
| Some(Ok(x)) => Ok(Some(x)), |
| Some(Err(e)) => Err(e), |
| None => Ok(None), |
| } |
| } |
| } |
| |
| // This is a separate function to reduce the code size of .expect() itself. |
| #[inline(never)] |
| #[cold] |
| fn expect_failed(msg: &str) -> ! { |
| panic!("{}", msg) |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // Trait implementations |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: Clone> Clone for Option<T> { |
| #[inline] |
| fn clone(&self) -> Self { |
| match self { |
| Some(x) => Some(x.clone()), |
| None => None, |
| } |
| } |
| |
| #[inline] |
| fn clone_from(&mut self, source: &Self) { |
| match (self, source) { |
| (Some(to), Some(from)) => to.clone_from(from), |
| (to, from) => *to = from.clone(), |
| } |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T> Default for Option<T> { |
| /// Returns [`None`][Option::None]. |
| #[inline] |
| fn default() -> Option<T> { None } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T> IntoIterator for Option<T> { |
| type Item = T; |
| type IntoIter = IntoIter<T>; |
| |
| /// Returns a consuming iterator over the possibly contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("string"); |
| /// let v: Vec<&str> = x.into_iter().collect(); |
| /// assert_eq!(v, ["string"]); |
| /// |
| /// let x = None; |
| /// let v: Vec<&str> = x.into_iter().collect(); |
| /// assert!(v.is_empty()); |
| /// ``` |
| #[inline] |
| fn into_iter(self) -> IntoIter<T> { |
| IntoIter { inner: Item { opt: self } } |
| } |
| } |
| |
| #[stable(since = "1.4.0", feature = "option_iter")] |
| impl<'a, T> IntoIterator for &'a Option<T> { |
| type Item = &'a T; |
| type IntoIter = Iter<'a, T>; |
| |
| fn into_iter(self) -> Iter<'a, T> { |
| self.iter() |
| } |
| } |
| |
| #[stable(since = "1.4.0", feature = "option_iter")] |
| impl<'a, T> IntoIterator for &'a mut Option<T> { |
| type Item = &'a mut T; |
| type IntoIter = IterMut<'a, T>; |
| |
| fn into_iter(self) -> IterMut<'a, T> { |
| self.iter_mut() |
| } |
| } |
| |
| #[stable(since = "1.12.0", feature = "option_from")] |
| impl<T> From<T> for Option<T> { |
| fn from(val: T) -> Option<T> { |
| Some(val) |
| } |
| } |
| |
| #[stable(feature = "option_ref_from_ref_option", since = "1.30.0")] |
| impl<'a, T> From<&'a Option<T>> for Option<&'a T> { |
| fn from(o: &'a Option<T>) -> Option<&'a T> { |
| o.as_ref() |
| } |
| } |
| |
| #[stable(feature = "option_ref_from_ref_option", since = "1.30.0")] |
| impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T> { |
| fn from(o: &'a mut Option<T>) -> Option<&'a mut T> { |
| o.as_mut() |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // The Option Iterators |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| #[derive(Clone, Debug)] |
| struct Item<A> { |
| opt: Option<A> |
| } |
| |
| impl<A> Iterator for Item<A> { |
| type Item = A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<A> { |
| self.opt.take() |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| match self.opt { |
| Some(_) => (1, Some(1)), |
| None => (0, Some(0)), |
| } |
| } |
| } |
| |
| impl<A> DoubleEndedIterator for Item<A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<A> { |
| self.opt.take() |
| } |
| } |
| |
| impl<A> ExactSizeIterator for Item<A> {} |
| impl<A> FusedIterator for Item<A> {} |
| unsafe impl<A> TrustedLen for Item<A> {} |
| |
| /// An iterator over a reference to the [`Some`] variant of an [`Option`]. |
| /// |
| /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none. |
| /// |
| /// This `struct` is created by the [`Option::iter`] function. |
| /// |
| /// [`Option`]: enum.Option.html |
| /// [`Some`]: enum.Option.html#variant.Some |
| /// [`Option::iter`]: enum.Option.html#method.iter |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[derive(Debug)] |
| pub struct Iter<'a, A: 'a> { inner: Item<&'a A> } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> Iterator for Iter<'a, A> { |
| type Item = &'a A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<&'a A> { self.inner.next() } |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> DoubleEndedIterator for Iter<'a, A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<&'a A> { self.inner.next_back() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> ExactSizeIterator for Iter<'_, A> {} |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<A> FusedIterator for Iter<'_, A> {} |
| |
| #[unstable(feature = "trusted_len", issue = "37572")] |
| unsafe impl<A> TrustedLen for Iter<'_, A> {} |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> Clone for Iter<'_, A> { |
| #[inline] |
| fn clone(&self) -> Self { |
| Iter { inner: self.inner.clone() } |
| } |
| } |
| |
| /// An iterator over a mutable reference to the [`Some`] variant of an [`Option`]. |
| /// |
| /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none. |
| /// |
| /// This `struct` is created by the [`Option::iter_mut`] function. |
| /// |
| /// [`Option`]: enum.Option.html |
| /// [`Some`]: enum.Option.html#variant.Some |
| /// [`Option::iter_mut`]: enum.Option.html#method.iter_mut |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[derive(Debug)] |
| pub struct IterMut<'a, A: 'a> { inner: Item<&'a mut A> } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> Iterator for IterMut<'a, A> { |
| type Item = &'a mut A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<&'a mut A> { self.inner.next() } |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> DoubleEndedIterator for IterMut<'a, A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<&'a mut A> { self.inner.next_back() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> ExactSizeIterator for IterMut<'_, A> {} |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<A> FusedIterator for IterMut<'_, A> {} |
| #[unstable(feature = "trusted_len", issue = "37572")] |
| unsafe impl<A> TrustedLen for IterMut<'_, A> {} |
| |
| /// An iterator over the value in [`Some`] variant of an [`Option`]. |
| /// |
| /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none. |
| /// |
| /// This `struct` is created by the [`Option::into_iter`] function. |
| /// |
| /// [`Option`]: enum.Option.html |
| /// [`Some`]: enum.Option.html#variant.Some |
| /// [`Option::into_iter`]: enum.Option.html#method.into_iter |
| #[derive(Clone, Debug)] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct IntoIter<A> { inner: Item<A> } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> Iterator for IntoIter<A> { |
| type Item = A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<A> { self.inner.next() } |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> DoubleEndedIterator for IntoIter<A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<A> { self.inner.next_back() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> ExactSizeIterator for IntoIter<A> {} |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<A> FusedIterator for IntoIter<A> {} |
| |
| #[unstable(feature = "trusted_len", issue = "37572")] |
| unsafe impl<A> TrustedLen for IntoIter<A> {} |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // FromIterator |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> { |
| /// Takes each element in the [`Iterator`]: if it is [`None`][Option::None], |
| /// no further elements are taken, and the [`None`][Option::None] is |
| /// returned. Should no [`None`][Option::None] occur, a container with the |
| /// values of each [`Option`] is returned. |
| /// |
| /// # Examples |
| /// |
| /// Here is an example which increments every integer in a vector. |
| /// We use the checked variant of `add` that returns `None` when the |
| /// calculation would result in an overflow. |
| /// |
| /// ``` |
| /// let items = vec![0_u16, 1, 2]; |
| /// |
| /// let res: Option<Vec<u16>> = items |
| /// .iter() |
| /// .map(|x| x.checked_add(1)) |
| /// .collect(); |
| /// |
| /// assert_eq!(res, Some(vec![1, 2, 3])); |
| /// ``` |
| /// |
| /// As you can see, this will return the expected, valid items. |
| /// |
| /// Here is another example that tries to subtract one from another list |
| /// of integers, this time checking for underflow: |
| /// |
| /// ``` |
| /// let items = vec![2_u16, 1, 0]; |
| /// |
| /// let res: Option<Vec<u16>> = items |
| /// .iter() |
| /// .map(|x| x.checked_sub(1)) |
| /// .collect(); |
| /// |
| /// assert_eq!(res, None); |
| /// ``` |
| /// |
| /// Since the last element is zero, it would underflow. Thus, the resulting |
| /// value is `None`. |
| /// |
| /// Here is a variation on the previous example, showing that no |
| /// further elements are taken from `iter` after the first `None`. |
| /// |
| /// ``` |
| /// let items = vec![3_u16, 2, 1, 10]; |
| /// |
| /// let mut shared = 0; |
| /// |
| /// let res: Option<Vec<u16>> = items |
| /// .iter() |
| /// .map(|x| { shared += x; x.checked_sub(2) }) |
| /// .collect(); |
| /// |
| /// assert_eq!(res, None); |
| /// assert_eq!(shared, 6); |
| /// ``` |
| /// |
| /// Since the third element caused an underflow, no further elements were taken, |
| /// so the final value of `shared` is 6 (= `3 + 2 + 1`), not 16. |
| /// |
| /// [`Iterator`]: ../iter/trait.Iterator.html |
| #[inline] |
| fn from_iter<I: IntoIterator<Item=Option<A>>>(iter: I) -> Option<V> { |
| // FIXME(#11084): This could be replaced with Iterator::scan when this |
| // performance bug is closed. |
| |
| struct Adapter<Iter> { |
| iter: Iter, |
| found_none: bool, |
| } |
| |
| impl<T, Iter: Iterator<Item=Option<T>>> Iterator for Adapter<Iter> { |
| type Item = T; |
| |
| #[inline] |
| fn next(&mut self) -> Option<T> { |
| match self.iter.next() { |
| Some(Some(value)) => Some(value), |
| Some(None) => { |
| self.found_none = true; |
| None |
| } |
| None => None, |
| } |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| if self.found_none { |
| (0, Some(0)) |
| } else { |
| let (_, upper) = self.iter.size_hint(); |
| (0, upper) |
| } |
| } |
| } |
| |
| let mut adapter = Adapter { iter: iter.into_iter(), found_none: false }; |
| let v: V = FromIterator::from_iter(adapter.by_ref()); |
| |
| if adapter.found_none { |
| None |
| } else { |
| Some(v) |
| } |
| } |
| } |
| |
| /// The error type that results from applying the try operator (`?`) to a `None` value. If you wish |
| /// to allow `x?` (where `x` is an `Option<T>`) to be converted into your error type, you can |
| /// implement `impl From<NoneError>` for `YourErrorType`. In that case, `x?` within a function that |
| /// returns `Result<_, YourErrorType>` will translate a `None` value into an `Err` result. |
| #[unstable(feature = "try_trait", issue = "42327")] |
| #[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)] |
| pub struct NoneError; |
| |
| #[unstable(feature = "try_trait", issue = "42327")] |
| impl<T> ops::Try for Option<T> { |
| type Ok = T; |
| type Error = NoneError; |
| |
| #[inline] |
| fn into_result(self) -> Result<T, NoneError> { |
| self.ok_or(NoneError) |
| } |
| |
| #[inline] |
| fn from_ok(v: T) -> Self { |
| Some(v) |
| } |
| |
| #[inline] |
| fn from_error(_: NoneError) -> Self { |
| None |
| } |
| } |
| |
| impl<T> Option<Option<T>> { |
| /// Converts from `Option<Option<T>>` to `Option<T>` |
| /// |
| /// # Examples |
| /// Basic usage: |
| /// ``` |
| /// #![feature(option_flattening)] |
| /// let x: Option<Option<u32>> = Some(Some(6)); |
| /// assert_eq!(Some(6), x.flatten()); |
| /// |
| /// let x: Option<Option<u32>> = Some(None); |
| /// assert_eq!(None, x.flatten()); |
| /// |
| /// let x: Option<Option<u32>> = None; |
| /// assert_eq!(None, x.flatten()); |
| /// ``` |
| /// Flattening once only removes one level of nesting: |
| /// ``` |
| /// #![feature(option_flattening)] |
| /// let x: Option<Option<Option<u32>>> = Some(Some(Some(6))); |
| /// assert_eq!(Some(Some(6)), x.flatten()); |
| /// assert_eq!(Some(6), x.flatten().flatten()); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "option_flattening", issue = "60258")] |
| pub fn flatten(self) -> Option<T> { |
| self.and_then(convert::identity) |
| } |
| } |