From f3024073f92b15d38b42241e65067f0ba796896c Mon Sep 17 00:00:00 2001
From: Scott McMurray <scottmcm@users.noreply.github.com>
Date: Tue, 25 Aug 2020 09:40:53 -0700
Subject: [PATCH] Suggest `mem::forget` if `mem::ManuallyDrop::new` isn't used
I think this communicates the intent better, and is shorter anyway.
---
library/core/src/mem/manually_drop.rs | 6 +++++-
library/core/src/mem/mod.rs | 2 +-
library/std/src/lazy.rs | 2 +-
3 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/library/core/src/mem/manually_drop.rs b/library/core/src/mem/manually_drop.rs
index e45aa86c0795a..aab0e96d83ab9 100644
--- a/library/core/src/mem/manually_drop.rs
+++ b/library/core/src/mem/manually_drop.rs
@@ -74,8 +74,12 @@ impl<T> ManuallyDrop<T> {
///
/// ```rust
/// use std::mem::ManuallyDrop;
- /// ManuallyDrop::new(Box::new(()));
+ /// let mut x = ManuallyDrop::new(String::from("Hello World!"));
+ /// x.truncate(5); // You can still safely operate on the value
+ /// assert_eq!(*x, "Hello");
+ /// // But `Drop` will not be run here
/// ```
+ #[must_use = "if you don't need the wrapper, you can use `mem::forget` instead"]
#[stable(feature = "manually_drop", since = "1.20.0")]
#[rustc_const_stable(feature = "const_manually_drop", since = "1.36.0")]
#[inline(always)]
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index 9107c570a8970..6d8ed2f4ffb1a 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -145,7 +145,7 @@ pub use crate::intrinsics::transmute;
#[rustc_const_stable(feature = "const_forget", since = "1.46.0")]
#[stable(feature = "rust1", since = "1.0.0")]
pub const fn forget<T>(t: T) {
- ManuallyDrop::new(t);
+ let _ = ManuallyDrop::new(t);
}
/// Like [`forget`], but also accepts unsized values.
diff --git a/library/std/src/lazy.rs b/library/std/src/lazy.rs
index f0548582d2f5d..d0f27df518505 100644
--- a/library/std/src/lazy.rs
+++ b/library/std/src/lazy.rs
@@ -293,7 +293,7 @@ impl<T> SyncOnceCell<T> {
// Don't drop this `SyncOnceCell`. We just moved out one of the fields, but didn't set
// the state to uninitialized.
- mem::ManuallyDrop::new(self);
+ mem::forget(self);
inner
}