From 736d19fdf73779242aca66b58d91269c1ae00970 Mon Sep 17 00:00:00 2001
From: Jeron Aldaron Lau <aldaronlau@gmail.com>
Date: Fri, 5 Aug 2022 13:23:50 -0500
Subject: [PATCH] Add `Weak`, a weak reference to a `Channel`

---
 CHANGELOG.md |  3 +++
 src/lib.rs   | 28 +++++++++++++++++++++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 988212e..bbfc6c1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://github.com/AldaronLau/semver).
 
 ## [0.5.0] - Unreleased
+### Added
+ - `Weak` reference to a `Channel`
+
 ### Removed
  - `Message`
 
diff --git a/src/lib.rs b/src/lib.rs
index a3b6b32..c008774 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -91,7 +91,7 @@
 
 extern crate alloc;
 
-use alloc::sync::Arc;
+use alloc::sync::{self, Arc};
 use core::{
     cell::UnsafeCell,
     future::Future,
@@ -271,6 +271,12 @@ impl<T: Send + Unpin, const S: usize, const R: usize> Channel<T, S, R> {
     pub async fn recv(&mut self) -> T {
         self.await
     }
+
+    /// Create a new corresponding [`Weak`] channel.
+    #[inline]
+    pub fn downgrade(&self) -> Weak<T, S, R> {
+        Weak(Arc::downgrade(&self.0))
+    }
 }
 
 impl<T, const S: usize, const R: usize> Future for Channel<T, S, R>
@@ -327,6 +333,26 @@ where
     }
 }
 
+/// A weak version of a `Channel`.
+#[derive(Debug, Default)]
+pub struct Weak<T: Send + Unpin, const S: usize = 1, const R: usize = 1>(
+    sync::Weak<Shared<T, S, R>>,
+);
+
+impl<T: Send + Unpin, const S: usize, const R: usize> Weak<T, S, R> {
+    /// Calling `upgrade()` will always return `None`.
+    #[inline]
+    pub fn new() -> Self {
+        Self(sync::Weak::new())
+    }
+
+    /// Attempt to upgrade the Weak channel to a [`Channel`].
+    #[inline]
+    pub fn upgrade(&self) -> Option<Channel<T, S, R>> {
+        Some(Channel(self.0.upgrade()?, usize::MAX))
+    }
+}
+
 /// A message in the process of being sent over a [`Channel`].
 #[derive(Debug)]
 struct Message<T: Send + Unpin, const S: usize, const R: usize>(