diff options
Diffstat (limited to '')
-rw-r--r-- | library/core/src/option.rs | 57 |
1 files changed, 51 insertions, 6 deletions
diff --git a/library/core/src/option.rs b/library/core/src/option.rs index 505d964e5..7cc00e3f8 100644 --- a/library/core/src/option.rs +++ b/library/core/src/option.rs @@ -72,6 +72,50 @@ //! } //! ``` //! +//! # The question mark operator, `?` +//! +//! Similar to the [`Result`] type, when writing code that calls many functions that return the +//! [`Option`] type, handling `Some`/`None` can be tedious. The question mark +//! operator, [`?`], hides some of the boilerplate of propagating values +//! up the call stack. +//! +//! It replaces this: +//! +//! ``` +//! # #![allow(dead_code)] +//! fn add_last_numbers(stack: &mut Vec<i32>) -> Option<i32> { +//! let a = stack.pop(); +//! let b = stack.pop(); +//! +//! match (a, b) { +//! (Some(x), Some(y)) => Some(x + y), +//! _ => None, +//! } +//! } +//! +//! ``` +//! +//! With this: +//! +//! ``` +//! # #![allow(dead_code)] +//! fn add_last_numbers(stack: &mut Vec<i32>) -> Option<i32> { +//! Some(stack.pop()? + stack.pop()?) +//! } +//! ``` +//! +//! *It's much nicer!* +//! +//! Ending the expression with [`?`] will result in the [`Some`]'s unwrapped value, unless the +//! result is [`None`], in which case [`None`] is returned early from the enclosing function. +//! +//! [`?`] can be used in functions that return [`Option`] because of the +//! early return of [`None`] that it provides. +//! +//! [`?`]: crate::ops::Try +//! [`Some`]: Some +//! [`None`]: None +//! //! # Representation //! //! Rust guarantees to optimize the following types `T` such that @@ -608,13 +652,14 @@ impl<T> Option<T> { /// /// # Examples /// - /// Converts an <code>Option<[String]></code> into an <code>Option<[usize]></code>, preserving - /// the original. The [`map`] method takes the `self` argument by value, consuming the original, - /// so this technique uses `as_ref` to first take an `Option` to a reference - /// to the value inside the original. + /// Calculates the length of an <code>Option<[String]></code> as an <code>Option<[usize]></code> + /// without moving the [`String`]. The [`map`] method takes the `self` argument by value, + /// consuming the original, so this technique uses `as_ref` to first take an `Option` to a + /// reference to the value inside the original. /// /// [`map`]: Option::map /// [String]: ../../std/string/struct.String.html "String" + /// [`String`]: ../../std/string/struct.String.html "String" /// /// ``` /// let text: Option<String> = Some("Hello, world!".to_string()); @@ -902,8 +947,8 @@ impl<T> Option<T> { /// /// # Examples /// - /// Converts an <code>Option<[String]></code> into an <code>Option<[usize]></code>, consuming - /// the original: + /// Calculates the length of an <code>Option<[String]></code> as an + /// <code>Option<[usize]></code>, consuming the original: /// /// [String]: ../../std/string/struct.String.html "String" /// ``` |