1use core::ptr;
2
3use super::{IsZero, Vec};
4use crate::alloc::Allocator;
5use crate::raw_vec::RawVec;
6
7// Specialization trait used for Vec::from_elem
8pub(super) trait SpecFromElem: Sized {
9 fn from_elem<A: Allocator>(elem: Self, n: usize, alloc: A) -> Vec<Self, A>;
10}
11
12impl<T: Clone> SpecFromElem for T {
13 #[track_caller]
14 default fn from_elem<A: Allocator>(elem: Self, n: usize, alloc: A) -> Vec<Self, A> {
15 let mut v: Vec = Vec::with_capacity_in(capacity:n, alloc);
16 v.extend_with(n, value:elem);
17 v
18 }
19}
20
21impl<T: Clone + IsZero> SpecFromElem for T {
22 #[inline]
23 #[track_caller]
24 default fn from_elem<A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
25 if elem.is_zero() {
26 return Vec { buf: RawVec::with_capacity_zeroed_in(capacity:n, alloc), len: n };
27 }
28 let mut v: Vec = Vec::with_capacity_in(capacity:n, alloc);
29 v.extend_with(n, value:elem);
30 v
31 }
32}
33
34impl SpecFromElem for i8 {
35 #[inline]
36 #[track_caller]
37 fn from_elem<A: Allocator>(elem: i8, n: usize, alloc: A) -> Vec<i8, A> {
38 if elem == 0 {
39 return Vec { buf: RawVec::with_capacity_zeroed_in(capacity:n, alloc), len: n };
40 }
41 let mut v: Vec = Vec::with_capacity_in(capacity:n, alloc);
42 unsafe {
43 ptr::write_bytes(dst:v.as_mut_ptr(), val:elem as u8, count:n);
44 v.set_len(new_len:n);
45 }
46 v
47 }
48}
49
50impl SpecFromElem for u8 {
51 #[inline]
52 #[track_caller]
53 fn from_elem<A: Allocator>(elem: u8, n: usize, alloc: A) -> Vec<u8, A> {
54 if elem == 0 {
55 return Vec { buf: RawVec::with_capacity_zeroed_in(capacity:n, alloc), len: n };
56 }
57 let mut v: Vec = Vec::with_capacity_in(capacity:n, alloc);
58 unsafe {
59 ptr::write_bytes(dst:v.as_mut_ptr(), val:elem, count:n);
60 v.set_len(new_len:n);
61 }
62 v
63 }
64}
65
66// A better way would be to implement this for all ZSTs which are `Copy` and have trivial `Clone`
67// but the latter cannot be detected currently
68impl SpecFromElem for () {
69 #[inline]
70 fn from_elem<A: Allocator>(_elem: (), n: usize, alloc: A) -> Vec<(), A> {
71 let mut v: Vec<(), A> = Vec::with_capacity_in(capacity:n, alloc);
72 // SAFETY: the capacity has just been set to `n`
73 // and `()` is a ZST with trivial `Clone` implementation
74 unsafe {
75 v.set_len(new_len:n);
76 }
77 v
78 }
79}
80