diff options
| -rw-r--r-- | library/core/src/mem/mod.rs | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs index a79a204e2c6..7ef84b0f5b5 100644 --- a/library/core/src/mem/mod.rs +++ b/library/core/src/mem/mod.rs @@ -909,6 +909,10 @@ pub fn take<T: Default>(dest: &mut T) -> T { #[rustc_const_unstable(feature = "const_replace", issue = "83164")] #[cfg_attr(not(test), rustc_diagnostic_item = "mem_replace")] pub const fn replace<T>(dest: &mut T, src: T) -> T { + // It may be tempting to use `swap` to avoid `unsafe` here. Don't! + // The compiler optimizes the implementation below to two `memcpy`s + // while `swap` would require at least three. See PR#83022 for details. + // SAFETY: We read from `dest` but directly write `src` into it afterwards, // such that the old value is not duplicated. Nothing is dropped and // nothing here can panic. |