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/target
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Cargo.lock
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[package]
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name = "futures-lite"
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version = "0.1.1"
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authors = ["Stjepan Glavina <stjepang@gmail.com>"]
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edition = "2018"
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description = "A lightweight subset of the futures crate"
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license = "Apache-2.0 OR MIT"
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[features]
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default = ["std"]
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std = []
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[dependencies]
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futures-core = "0.3.5"
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futures-io = { version = "0.3.5", default-features = false, features = ["std"] }
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use std::fmt;
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use std::pin::Pin;
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use std::task::{Context, Poll};
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pub use futures_core::{Future, Stream};
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pub use futures_io::{AsyncRead, AsyncSeek, AsyncWrite};
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#[macro_export]
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macro_rules! ready {
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($e:expr $(,)?) => {
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match $e {
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std::task::Poll::Ready(t) => t,
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std::task::Poll::Pending => return std::task::Poll::Pending,
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}
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};
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}
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#[macro_export]
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macro_rules! pin {
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($($x:ident),* $(,)?) => {
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$(
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let mut $x = $x;
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#[allow(unused_mut)]
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let mut $x = unsafe {
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std::pin::Pin::new_unchecked(&mut $x)
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};
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)*
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}
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}
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pub mod future {
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use super::*;
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/// Future for the [`poll_fn`] function.
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct PollFn<F> {
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f: F,
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}
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impl<F> Unpin for PollFn<F> {}
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/// Creates a new future wrapping around a function returning [`Poll`].
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///
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/// Polling the returned future delegates to the wrapped function.
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pub fn poll_fn<T, F>(f: F) -> PollFn<F>
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where
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F: FnMut(&mut Context<'_>) -> Poll<T>,
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{
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PollFn { f }
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}
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impl<F> fmt::Debug for PollFn<F> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("PollFn").finish()
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}
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}
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impl<T, F> Future for PollFn<F>
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where
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F: FnMut(&mut Context<'_>) -> Poll<T>,
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{
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type Output = T;
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
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(&mut self.f)(cx)
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}
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}
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}
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pub mod stream {
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use super::*;
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/// Creates a `Stream` from a seed and a closure returning a `Future`.
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///
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/// This function is the dual for the `Stream::fold()` adapter: while
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/// `Stream::fold()` reduces a `Stream` to one single value, `unfold()` creates a
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/// `Stream` from a seed value.
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///
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/// `unfold()` will call the provided closure with the provided seed, then wait
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/// for the returned `Future` to complete with `(a, b)`. It will then yield the
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/// value `a`, and use `b` as the next internal state.
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///
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/// If the closure returns `None` instead of `Some(Future)`, then the `unfold()`
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/// will stop producing items and return `Poll::Ready(None)` in future
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/// calls to `poll()`.
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///
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/// This function can typically be used when wanting to go from the "world of
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/// futures" to the "world of streams": the provided closure can build a
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/// `Future` using other library functions working on futures, and `unfold()`
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/// will turn it into a `Stream` by repeating the operation.
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pub fn unfold<T, F, Fut, Item>(init: T, f: F) -> Unfold<T, F, Fut>
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where
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F: FnMut(T) -> Fut,
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Fut: Future<Output = Option<(Item, T)>>,
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{
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Unfold {
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f,
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state: Some(init),
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fut: None,
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}
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}
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/// Stream for the [`unfold`] function.
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#[must_use = "streams do nothing unless polled"]
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pub struct Unfold<T, F, Fut> {
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f: F,
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state: Option<T>,
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fut: Option<Fut>,
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}
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impl<T, F, Fut> fmt::Debug for Unfold<T, F, Fut>
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where
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T: fmt::Debug,
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Fut: fmt::Debug,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("Unfold")
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.field("state", &self.state)
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.field("fut", &self.fut)
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.finish()
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}
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}
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impl<T, F, Fut, Item> Stream for Unfold<T, F, Fut>
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where
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F: FnMut(T) -> Fut,
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Fut: Future<Output = Option<(Item, T)>>,
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{
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type Item = Item;
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fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
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let mut this = unsafe { self.get_unchecked_mut() };
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if let Some(state) = this.state.take() {
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this.fut = Some((this.f)(state));
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}
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let fut = unsafe {
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Pin::new_unchecked(
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this.fut
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.as_mut()
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.expect("Unfold must not be polled after it returned `Poll::Ready(None)`"),
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)
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};
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let step = futures_core::ready!(fut.poll(cx));
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this.fut = None;
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if let Some((item, next_state)) = step {
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this.state = Some(next_state);
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Poll::Ready(Some(item))
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} else {
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Poll::Ready(None)
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}
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}
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}
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}
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