Avoid allocations and copying in Vec::leak

mbrubeck · mbrubeck · commit 58b1a127d66b · 2021-09-28T13:23:54.000-07:00
Don't shrink the Vec (by calling into_boxed_slice) before leaking it.
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
@@ -1976,7 +1976,8 @@ impl<T, A: Allocator> Vec<T, A> {
     where
         A: 'a,
     {
-        Box::leak(self.into_boxed_slice())
+        let mut me = ManuallyDrop::new(self);
+        unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }
     }
 
     /// Returns the remaining spare capacity of the vector as a slice of

Original file line number	Diff line number	Diff line change
`@@ -1976,7 +1976,8 @@ impl<T, A: Allocator> Vec<T, A> {`
`1976`	`1976`	`where`
`1977`	`1977`	`A: 'a,`
`1978`	`1978`	`{`
`1979`		`- Box::leak(self.into_boxed_slice())`
	`1979`	`+ let mut me = ManuallyDrop::new(self);`
	`1980`	`+ unsafe { slice::from_raw_parts_mut(me.as_mut_ptr(), me.len) }`
`1980`	`1981`	`}`
`1981`	`1982`
`1982`	`1983`	`/// Returns the remaining spare capacity of the vector as a slice of`