src/poll_fn.rs

   1 //! `poll_fn` reimplementation as it is otherwise the only thing we need from the futures crate.
   2 //!
   3 //! Our `futures` crate dependency is optional.
   4
   5 use std::future::Future;
   6 use std::pin::Pin;
   7 use std::task::{Context, Poll};
   8
   9 pub struct PollFn<F> {
  10     func: Option<F>,
  11 }
  12
  13 pub fn poll_fn<F, R>(func: F) -> PollFn<F>
  14 where
  15     F: FnMut(&mut Context) -> Poll<R>,
  16 {
  17     PollFn { func: Some(func) }
  18 }
  19
  20 impl<F, R> Future for PollFn<F>
  21 where
  22     F: FnMut(&mut Context) -> Poll<R>,
  23 {
  24     type Output = R;
  25
  26     fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
  27         let this = unsafe { self.get_unchecked_mut() };
  28         match &mut this.func {
  29             None => panic!("poll() after Ready"),
  30             Some(func) => {
  31                 let res = func(cx);
  32                 if res.is_ready() {
  33                     this.func = None;
  34                 }
  35                 res
  36             }
  37         }
  38     }
  39 }