summaryrefslogtreecommitdiffstats
path: root/third_party/rust/hyper/src/common/lazy.rs
diff options
context:
space:
mode:
Diffstat (limited to 'third_party/rust/hyper/src/common/lazy.rs')
-rw-r--r--third_party/rust/hyper/src/common/lazy.rs76
1 files changed, 76 insertions, 0 deletions
diff --git a/third_party/rust/hyper/src/common/lazy.rs b/third_party/rust/hyper/src/common/lazy.rs
new file mode 100644
index 0000000000..2722077303
--- /dev/null
+++ b/third_party/rust/hyper/src/common/lazy.rs
@@ -0,0 +1,76 @@
+use pin_project_lite::pin_project;
+
+use super::{task, Future, Pin, Poll};
+
+pub(crate) trait Started: Future {
+ fn started(&self) -> bool;
+}
+
+pub(crate) fn lazy<F, R>(func: F) -> Lazy<F, R>
+where
+ F: FnOnce() -> R,
+ R: Future + Unpin,
+{
+ Lazy {
+ inner: Inner::Init { func },
+ }
+}
+
+// FIXME: allow() required due to `impl Trait` leaking types to this lint
+pin_project! {
+ #[allow(missing_debug_implementations)]
+ pub(crate) struct Lazy<F, R> {
+ #[pin]
+ inner: Inner<F, R>,
+ }
+}
+
+pin_project! {
+ #[project = InnerProj]
+ #[project_replace = InnerProjReplace]
+ enum Inner<F, R> {
+ Init { func: F },
+ Fut { #[pin] fut: R },
+ Empty,
+ }
+}
+
+impl<F, R> Started for Lazy<F, R>
+where
+ F: FnOnce() -> R,
+ R: Future,
+{
+ fn started(&self) -> bool {
+ match self.inner {
+ Inner::Init { .. } => false,
+ Inner::Fut { .. } | Inner::Empty => true,
+ }
+ }
+}
+
+impl<F, R> Future for Lazy<F, R>
+where
+ F: FnOnce() -> R,
+ R: Future,
+{
+ type Output = R::Output;
+
+ fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+ let mut this = self.project();
+
+ if let InnerProj::Fut { fut } = this.inner.as_mut().project() {
+ return fut.poll(cx);
+ }
+
+ match this.inner.as_mut().project_replace(Inner::Empty) {
+ InnerProjReplace::Init { func } => {
+ this.inner.set(Inner::Fut { fut: func() });
+ if let InnerProj::Fut { fut } = this.inner.project() {
+ return fut.poll(cx);
+ }
+ unreachable!()
+ }
+ _ => unreachable!("lazy state wrong"),
+ }
+ }
+}