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