f6cb45ad01
add `Vec::extend_from_within` method under `vec_extend_from_within` feature gate
Implement <https://github.com/rust-lang/rfcs/pull/2714>
### tl;dr
This PR adds a `extend_from_within` method to `Vec` which allows copying elements from a range to the end:
```rust
#![feature(vec_extend_from_within)]
let mut vec = vec![0, 1, 2, 3, 4];
vec.extend_from_within(2..);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);
vec.extend_from_within(..2);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);
vec.extend_from_within(4..8);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);
```
### Implementation notes
Originally I've copied `@Shnatsel's` [implementation](690742a0de/src/lib.rs (L74)) with some minor changes to support other ranges:
```rust
pub fn append_from_within<R>(&mut self, src: R)
where
T: Copy,
R: RangeBounds<usize>,
{
let len = self.len();
let Range { start, end } = src.assert_len(len);;
let count = end - start;
self.reserve(count);
unsafe {
// This is safe because `reserve()` above succeeded,
// so `self.len() + count` did not overflow usize
ptr::copy_nonoverlapping(
self.get_unchecked(src.start),
self.as_mut_ptr().add(len),
count,
);
self.set_len(len + count);
}
}
```
But then I've realized that this duplicates most of the code from (private) `Vec::append_elements`, so I've used it instead.
Then I've applied `@KodrAus` suggestions from https://github.com/rust-lang/rust/pull/79015#issuecomment-727200852.
63 lines
1.6 KiB
Rust
63 lines
1.6 KiB
Rust
#![feature(allocator_api)]
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#![feature(box_syntax)]
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#![feature(cow_is_borrowed)]
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#![feature(const_cow_is_borrowed)]
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#![feature(drain_filter)]
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#![feature(exact_size_is_empty)]
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#![feature(new_uninit)]
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#![feature(pattern)]
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#![feature(str_split_once)]
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#![feature(trusted_len)]
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#![feature(try_reserve)]
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#![feature(unboxed_closures)]
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#![feature(associated_type_bounds)]
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#![feature(binary_heap_into_iter_sorted)]
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#![feature(binary_heap_drain_sorted)]
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#![feature(slice_ptr_get)]
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#![feature(binary_heap_retain)]
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#![feature(inplace_iteration)]
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#![feature(iter_map_while)]
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#![feature(vecdeque_binary_search)]
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#![feature(slice_group_by)]
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#![feature(vec_extend_from_within)]
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use std::collections::hash_map::DefaultHasher;
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use std::hash::{Hash, Hasher};
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mod arc;
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mod binary_heap;
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mod borrow;
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mod boxed;
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mod btree_set_hash;
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mod cow_str;
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mod fmt;
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mod heap;
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mod linked_list;
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mod rc;
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mod slice;
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mod str;
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mod string;
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mod vec;
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mod vec_deque;
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fn hash<T: Hash>(t: &T) -> u64 {
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let mut s = DefaultHasher::new();
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t.hash(&mut s);
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s.finish()
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}
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// FIXME: Instantiated functions with i128 in the signature is not supported in Emscripten.
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// See https://github.com/kripken/emscripten-fastcomp/issues/169
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#[cfg(not(target_os = "emscripten"))]
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#[test]
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fn test_boxed_hasher() {
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let ordinary_hash = hash(&5u32);
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let mut hasher_1 = Box::new(DefaultHasher::new());
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5u32.hash(&mut hasher_1);
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assert_eq!(ordinary_hash, hasher_1.finish());
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let mut hasher_2 = Box::new(DefaultHasher::new()) as Box<dyn Hasher>;
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5u32.hash(&mut hasher_2);
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assert_eq!(ordinary_hash, hasher_2.finish());
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}
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