Add #[must_use] to non-mutating verb methods

[rust.git] / library / alloc / src / sync.rs

diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 1d4216d7d571af24f947a39bc7695773ecd0f8f7..905e3d72a458c65254b8beebd0cf924c9791e783 100644 (file)
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -146,7 +146,7 @@ macro_rules! acquire {
 /// use std::sync::Arc;
 ///
 /// let my_arc = Arc::new(());
-/// Arc::downgrade(&my_arc);
+/// let my_weak = Arc::downgrade(&my_arc);
 /// ```
 ///
 /// `Arc<T>`'s implementations of traits like `Clone` may also be called using
@@ -897,6 +897,8 @@ pub unsafe fn from_raw(ptr: *const T) -> Self {
     ///
     /// let weak_five = Arc::downgrade(&five);
     /// ```
+    #[must_use = "this returns a new `Weak` pointer, \
+                  without modifying the original `Arc`"]
     #[stable(feature = "arc_weak", since = "1.4.0")]
     pub fn downgrade(this: &Self) -> Weak<T> {
         // This Relaxed is OK because we're checking the value in the CAS
@@ -1861,6 +1863,8 @@ impl<T: ?Sized> Weak<T> {
     ///
     /// assert!(weak_five.upgrade().is_none());
     /// ```
+    #[must_use = "this returns a new `Arc`, \
+                  without modifying the original weak pointer"]
     #[stable(feature = "arc_weak", since = "1.4.0")]
     pub fn upgrade(&self) -> Option<Arc<T>> {
         // We use a CAS loop to increment the strong count instead of a