library/core/src/iter/sources/from_generator.rs

   1 use crate::ops::{Generator, GeneratorState};
   2 use crate::pin::Pin;
   3
   4 /// Creates a new iterator where each iteration calls the provided generator.
   5 ///
   6 /// Similar to [`iter::from_fn`].
   7 ///
   8 /// [`iter::from_fn`]: crate::iter::from_fn
   9 ///
  10 /// # Examples
  11 ///
  12 /// ```
  13 /// #![feature(generators)]
  14 /// #![feature(iter_from_generator)]
  15 ///
  16 /// let it = std::iter::from_generator(|| {
  17 ///     yield 1;
  18 ///     yield 2;
  19 ///     yield 3;
  20 /// });
  21 /// let v: Vec<_> = it.collect();
  22 /// assert_eq!(v, [1, 2, 3]);
  23 /// ```
  24 #[inline]
  25 #[unstable(feature = "iter_from_generator", issue = "43122", reason = "generators are unstable")]
  26 pub fn from_generator<G: Generator<Return = ()> + Unpin>(
  27     generator: G,
  28 ) -> impl Iterator<Item = G::Yield> {
  29     FromGenerator(generator)
  30 }
  31
  32 struct FromGenerator<G>(G);
  33
  34 impl<G: Generator<Return = ()> + Unpin> Iterator for FromGenerator<G> {
  35     type Item = G::Yield;
  36
  37     fn next(&mut self) -> Option<Self::Item> {
  38         match Pin::new(&mut self.0).resume(()) {
  39             GeneratorState::Yielded(n) => Some(n),
  40             GeneratorState::Complete(()) => None,
  41         }
  42     }
  43 }