diff --git a/library/alloc/src/vec/spec_from_elem.rs b/library/alloc/src/vec/spec_from_elem.rs index da43d17bf36..4e4150d9435 100644 --- a/library/alloc/src/vec/spec_from_elem.rs +++ b/library/alloc/src/vec/spec_from_elem.rs @@ -36,12 +36,12 @@ impl SpecFromElem for i8 { if elem == 0 { return Vec { buf: RawVec::with_capacity_zeroed_in(n, alloc), len: n }; } + let mut v = Vec::with_capacity_in(n, alloc); unsafe { - let mut v = Vec::with_capacity_in(n, alloc); ptr::write_bytes(v.as_mut_ptr(), elem as u8, n); v.set_len(n); - v } + v } } @@ -51,11 +51,26 @@ impl SpecFromElem for u8 { if elem == 0 { return Vec { buf: RawVec::with_capacity_zeroed_in(n, alloc), len: n }; } + let mut v = Vec::with_capacity_in(n, alloc); unsafe { - let mut v = Vec::with_capacity_in(n, alloc); ptr::write_bytes(v.as_mut_ptr(), elem, n); v.set_len(n); - v } + v + } +} + +// A better way would be to implement this for all ZSTs which are `Copy` and have trivial `Clone` +// but this cannot be implemented currently +impl SpecFromElem for () { + #[inline] + fn from_elem(elem: (), n: usize, alloc: A) -> Vec<(), A> { + let mut v = Vec::with_capacity_in(n, alloc); + // SAFETY: the capacity has just been set to `n` and `()` + // is a ZST with trivial `Clone` implementation + unsafe { + v.set_len(n); + } + v } }