1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
#![stable(feature = "futures_api", since = "1.36.0")]

use crate::convert;
use crate::ops::{self, ControlFlow};
use crate::result::Result;

/// Indicates whether a value is available or if the current task has been
/// scheduled to receive a wakeup instead.
#[must_use = "this `Poll` may be a `Pending` variant, which should be handled"]
#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
#[stable(feature = "futures_api", since = "1.36.0")]
pub enum Poll<T> {
    /// Represents that a value is immediately ready.
    #[lang = "Ready"]
    #[stable(feature = "futures_api", since = "1.36.0")]
    Ready(#[stable(feature = "futures_api", since = "1.36.0")] T),

    /// Represents that a value is not ready yet.
    ///
    /// When a function returns `Pending`, the function *must* also
    /// ensure that the current task is scheduled to be awoken when
    /// progress can be made.
    #[lang = "Pending"]
    #[stable(feature = "futures_api", since = "1.36.0")]
    Pending,
}

impl<T> Poll<T> {
    /// 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
        F: FnOnce(T) -> U,
    {
        match self {
            Poll::Ready(t) => Poll::Ready(f(t)),
            Poll::Pending => Poll::Pending,
        }
    }

    /// 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")]
    pub const fn is_ready(&self) -> bool {
        matches!(*self, Poll::Ready(_))
    }

    /// 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")]
    pub const fn is_pending(&self) -> bool {
        !self.is_ready()
    }
}

impl<T, E> Poll<Result<T, E>> {
    /// 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
        F: FnOnce(T) -> U,
    {
        match self {
            Poll::Ready(Ok(t)) => Poll::Ready(Ok(f(t))),
            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
            Poll::Pending => Poll::Pending,
        }
    }

    /// 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
        F: FnOnce(E) -> U,
    {
        match self {
            Poll::Ready(Ok(t)) => Poll::Ready(Ok(t)),
            Poll::Ready(Err(e)) => Poll::Ready(Err(f(e))),
            Poll::Pending => Poll::Pending,
        }
    }
}

impl<T, E> Poll<Option<Result<T, E>>> {
    /// 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
        F: FnOnce(T) -> U,
    {
        match self {
            Poll::Ready(Some(Ok(t))) => Poll::Ready(Some(Ok(f(t)))),
            Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e))),
            Poll::Ready(None) => Poll::Ready(None),
            Poll::Pending => Poll::Pending,
        }
    }

    /// 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
        F: FnOnce(E) -> U,
    {
        match self {
            Poll::Ready(Some(Ok(t))) => Poll::Ready(Some(Ok(t))),
            Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(f(e)))),
            Poll::Ready(None) => Poll::Ready(None),
            Poll::Pending => Poll::Pending,
        }
    }
}

#[stable(feature = "futures_api", since = "1.36.0")]
impl<T> From<T> for Poll<T> {
    /// Convert to a `Ready` variant.
    ///
    /// # Example
    ///
    /// ```
    /// # use core::task::Poll;
    /// assert_eq!(Poll::from(true), Poll::Ready(true));
    /// ```
    fn from(t: T) -> Poll<T> {
        Poll::Ready(t)
    }
}

#[unstable(feature = "try_trait_v2", issue = "84277")]
impl<T, E> ops::TryV2 for Poll<Result<T, E>> {
    type Output = Poll<T>;
    type Residual = Result<convert::Infallible, E>;

    #[inline]
    fn from_output(c: Self::Output) -> Self {
        c.map(Ok)
    }

    #[inline]
    fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
        match self {
            Poll::Ready(Ok(x)) => ControlFlow::Continue(Poll::Ready(x)),
            Poll::Ready(Err(e)) => ControlFlow::Break(Err(e)),
            Poll::Pending => ControlFlow::Continue(Poll::Pending),
        }
    }
}

#[unstable(feature = "try_trait_v2", issue = "84277")]
impl<T, E, F: From<E>> ops::FromResidual<Result<convert::Infallible, E>> for Poll<Result<T, F>> {
    #[inline]
    fn from_residual(x: Result<convert::Infallible, E>) -> Self {
        match x {
            Err(e) => Poll::Ready(Err(From::from(e))),
        }
    }
}

#[unstable(feature = "try_trait_v2", issue = "84277")]
impl<T, E> ops::TryV2 for Poll<Option<Result<T, E>>> {
    type Output = Poll<Option<T>>;
    type Residual = Result<convert::Infallible, E>;

    #[inline]
    fn from_output(c: Self::Output) -> Self {
        c.map(|x| x.map(Ok))
    }

    #[inline]
    fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
        match self {
            Poll::Ready(Some(Ok(x))) => ControlFlow::Continue(Poll::Ready(Some(x))),
            Poll::Ready(Some(Err(e))) => ControlFlow::Break(Err(e)),
            Poll::Ready(None) => ControlFlow::Continue(Poll::Ready(None)),
            Poll::Pending => ControlFlow::Continue(Poll::Pending),
        }
    }
}

#[unstable(feature = "try_trait_v2", issue = "84277")]
impl<T, E, F: From<E>> ops::FromResidual<Result<convert::Infallible, E>>
    for Poll<Option<Result<T, F>>>
{
    #[inline]
    fn from_residual(x: Result<convert::Infallible, E>) -> Self {
        match x {
            Err(e) => Poll::Ready(Some(Err(From::from(e)))),
        }
    }
}