Some functions in future module to no_std

src/future/mod.rs

@@ -48,17 +48,14 @@
 
 cfg_alloc! {
     pub use future::Future;
-    pub(crate) mod future;
-}
-
-cfg_std! {
+    pub use ready::ready;
     pub use pending::pending;
     pub use poll_fn::poll_fn;
-    pub use ready::ready;
 
+    pub(crate) mod future;
+    mod ready;
     mod pending;
     mod poll_fn;
-    mod ready;
 }
 
 cfg_default! {

src/future/pending.rs

@@ -1,6 +1,6 @@
-use std::future::Future;
-use std::marker::PhantomData;
-use std::pin::Pin;
+use core::future::Future;
+use core::marker::PhantomData;
+use core::pin::Pin;
 
 use crate::task::{Context, Poll};
 
@@ -24,14 +24,17 @@ use crate::task::{Context, Poll};
 /// #
 /// # })
 /// ```
-pub async fn pending<T>() -> T {
-    let fut = Pending {
+pub fn pending<T>() -> Pending<T> {
+    Pending {
         _marker: PhantomData,
-    };
-    fut.await
+    }
 }
 
-struct Pending<T> {
+/// This future is constructed by the [`pending`] function.
+///
+/// [`pending`]: fn.pending.html
+#[derive(Debug)]
+pub struct Pending<T> {
     _marker: PhantomData<T>,
 }
 

src/future/poll_fn.rs

@@ -1,5 +1,5 @@
-use std::pin::Pin;
-use std::future::Future;
+use core::future::Future;
+use core::pin::Pin;
 
 use crate::task::{Context, Poll};
 
@@ -23,15 +23,18 @@ use crate::task::{Context, Poll};
 /// #
 /// # })
 /// ```
-pub async fn poll_fn<F, T>(f: F) -> T
+pub fn poll_fn<F, T>(f: F) -> PollFn<F>
 where
     F: FnMut(&mut Context<'_>) -> Poll<T>,
 {
-    let fut = PollFn { f };
-    fut.await
+    PollFn { f }
 }
 
-struct PollFn<F> {
+/// This future is constructed by the [`poll_fn`] function.
+///
+/// [`poll_fn`]: fn.poll_fn.html
+#[derive(Debug)]
+pub struct PollFn<F> {
     f: F,
 }
 

src/future/ready.rs

@@ -1,3 +1,8 @@
+use core::future::Future;
+use core::pin::Pin;
+
+use crate::task::{Context, Poll};
+
 /// Resolves to the provided value.
 ///
 /// This function is an async version of [`std::convert::identity`].
@@ -15,6 +20,22 @@
 /// #
 /// # })
 /// ```
-pub async fn ready<T>(val: T) -> T {
-    val
+pub fn ready<T>(val: T) -> Ready<T> {
+    Ready(Some(val))
+}
+
+/// This future is constructed by the [`ready`] function.
+///
+/// [`ready`]: fn.ready.html
+#[derive(Debug)]
+pub struct Ready<T>(Option<T>);
+
+impl<T> Unpin for Ready<T> {}
+
+impl<T> Future for Ready<T> {
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<T> {
+        Poll::Ready(self.0.take().unwrap())
+    }
 }