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Auto merge of #86598 - yoshuawuyts:poll-method-docs, r=JohnTitor

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Add examples to the various methods of `core::task::Poll`

This improves the documentation of the various methods of [`core::task::Poll`](https://doc.rust-lang.org/std/task/enum.Poll.html). These currently have fairly simple docs with no examples. This PR changes these methods to be closer to `core::option::Option` and adds usage examples (and importantly: tests!) to `Poll`'s methods.

cc/ `@rust-lang/wg-async-foundations`

## Screenshots

<details>
<summary>View generated rustdoc page</summary>
<image src="https://user-images.githubusercontent.com/2467194/123286616-59ee9b00-d50e-11eb-9e02-40269070f904.png" alt="Poll in core::task"></details>
This commit is contained in:
bors 2021-07-04 20:00:57 +00:00
commit b3d11f95cc
1 changed files with 100 additions and 7 deletions
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107
library/core/src/task/poll.rs
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@ -26,7 +26,21 @@ pub enum Poll<T> {
}
impl<T> Poll<T> {
/// Changes the ready value of this `Poll` with the closure provided.
/// Maps a `Poll<T>` to `Poll<U>` by applying a function to a contained value.
///
/// # Examples
///
/// Converts a `Poll<`[`String`]`>` into an `Poll<`[`usize`]`>`, consuming the original:
///
/// [`String`]: ../../std/string/struct.String.html
/// ```
/// # use core::task::Poll;
/// let poll_some_string = Poll::Ready(String::from("Hello, World!"));
/// // `Poll::map` takes self *by value*, consuming `poll_some_string`
/// let poll_some_len = poll_some_string.map(|s| s.len());
///
/// assert_eq!(poll_some_len, Poll::Ready(13));
/// ```
#[stable(feature = "futures_api", since = "1.36.0")]
pub fn map<U, F>(self, f: F) -> Poll<U>
where
@ -38,7 +52,18 @@ impl<T> Poll<T> {
}
}
/// Returns `true` if this is `Poll::Ready`
/// Returns `true` if the poll is a [`Poll::Ready`] value.
///
/// # Examples
///
/// ```
/// # use core::task::Poll;
/// let x: Poll<u32> = Poll::Ready(2);
/// assert_eq!(x.is_ready(), true);
///
/// let x: Poll<u32> = Poll::Pending;
/// assert_eq!(x.is_ready(), false);
/// ```
#[inline]
#[rustc_const_stable(feature = "const_poll", since = "1.49.0")]
#[stable(feature = "futures_api", since = "1.36.0")]
@ -46,7 +71,20 @@ impl<T> Poll<T> {
matches!(*self, Poll::Ready(_))
}
/// Returns `true` if this is `Poll::Pending`
/// Returns `true` if the poll is a [`Pending`] value.
///
/// [`Pending`]: Poll::Pending
///
/// # Examples
///
/// ```
/// # use core::task::Poll;
/// let x: Poll<u32> = Poll::Ready(2);
/// assert_eq!(x.is_pending(), false);
///
/// let x: Poll<u32> = Poll::Pending;
/// assert_eq!(x.is_pending(), true);
/// ```
#[inline]
#[rustc_const_stable(feature = "const_poll", since = "1.49.0")]
#[stable(feature = "futures_api", since = "1.36.0")]
@ -56,7 +94,20 @@ impl<T> Poll<T> {
}
impl<T, E> Poll<Result<T, E>> {
/// Changes the success value of this `Poll` with the closure provided.
/// Maps a `Poll<Result<T, E>>` to `Poll<Result<U, E>>` by applying a
/// function to a contained `Poll::Ready(Ok)` value, leaving all other
/// variants untouched.
///
/// This function can be used to compose the results of two functions.
///
/// # Examples
///
/// ```
/// # use core::task::Poll;
/// let res: Poll<Result<u8, _>> = Poll::Ready("12".parse());
/// let squared = res.map_ok(|n| n * n);
/// assert_eq!(squared, Poll::Ready(Ok(144)));
/// ```
#[stable(feature = "futures_api", since = "1.36.0")]
pub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>
where
@ -69,7 +120,21 @@ impl<T, E> Poll<Result<T, E>> {
}
}
/// Changes the error value of this `Poll` with the closure provided.
/// Maps a `Poll::Ready<Result<T, E>>` to `Poll::Ready<Result<T, F>>` by
/// applying a function to a contained `Poll::Ready(Err)` value, leaving all other
/// variants untouched.
///
/// This function can be used to pass through a successful result while handling
/// an error.
///
/// # Examples
///
/// ```
/// # use core::task::Poll;
/// let res: Poll<Result<u8, _>> = Poll::Ready("oops".parse());
/// let res = res.map_err(|_| 0_u8);
/// assert_eq!(res, Poll::Ready(Err(0)));
/// ```
#[stable(feature = "futures_api", since = "1.36.0")]
pub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>
where
@ -84,7 +149,20 @@ impl<T, E> Poll<Result<T, E>> {
}
impl<T, E> Poll<Option<Result<T, E>>> {
/// Changes the success value of this `Poll` with the closure provided.
/// Maps a `Poll<Option<Result<T, E>>>` to `Poll<Option<Result<U, E>>>` by
/// applying a function to a contained `Poll::Ready(Some(Ok))` value,
/// leaving all other variants untouched.
///
/// This function can be used to compose the results of two functions.
///
/// # Examples
///
/// ```
/// # use core::task::Poll;
/// let res: Poll<Option<Result<u8, _>>> = Poll::Ready(Some("12".parse()));
/// let squared = res.map_ok(|n| n * n);
/// assert_eq!(squared, Poll::Ready(Some(Ok(144))));
/// ```
#[stable(feature = "poll_map", since = "1.51.0")]
pub fn map_ok<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>
where
@ -98,7 +176,22 @@ impl<T, E> Poll<Option<Result<T, E>>> {
}
}
/// Changes the error value of this `Poll` with the closure provided.
/// Maps a `Poll::Ready<Option<Result<T, E>>>` to
/// `Poll::Ready<Option<Result<T, F>>>` by applying a function to a
/// contained `Poll::Ready(Some(Err))` value, leaving all other variants
/// untouched.
///
/// This function can be used to pass through a successful result while handling
/// an error.
///
/// # Examples
///
/// ```
/// # use core::task::Poll;
/// let res: Poll<Option<Result<u8, _>>> = Poll::Ready(Some("oops".parse()));
/// let res = res.map_err(|_| 0_u8);
/// assert_eq!(res, Poll::Ready(Some(Err(0))));
/// ```
#[stable(feature = "poll_map", since = "1.51.0")]
pub fn map_err<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>
where