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rust/library
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bors f6cb45ad01 Auto merge of #79015 - WaffleLapkin:vec_append_from_within, r=KodrAus 
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.
2021-02-02 09:12:53 +00:00
..
alloc Auto merge of #79015 - WaffleLapkin:vec_append_from_within, r=KodrAus 2021-02-02 09:12:53 +00:00
backtrace@af078ecc0b std: Update the backtrace crate submodule 2020-11-20 11:56:07 -08:00
core Auto merge of #80851 - m-ou-se:panic-2021, r=petrochenkov 2021-02-01 10:25:31 +00:00
panic_abort slightly more typed interface to panic implementation 2020-12-21 13:37:59 +01:00
panic_unwind stabilize int_bits_const 2021-01-31 21:50:47 +10:00
proc_macro Bump bootstrap compiler to 1.50 beta 2020-12-30 09:27:19 -05:00
profiler_builtins Fix warning whe building profiler_builtins crate 2020-09-04 15:10:29 +02:00
rtstartup Bump bootstrap compiler to 1.50 beta 2020-12-30 09:27:19 -05:00
rustc-std-workspace-alloc
rustc-std-workspace-core Fix rustc-std-workspace-core documentation 2020-12-20 15:23:21 +08:00
rustc-std-workspace-std
std Rollup merge of #81598 - sivadeilra:windows_dll_imports_fix_x86, r=m-ou-se 2021-02-01 14:29:45 +01:00
stdarch@9c732a56f6 Update stdarch submodule 2020-12-21 00:00:00 +00:00
term
test Rollup merge of #80053 - gilescope:include-ignore, r=m-ou-se 2021-01-31 01:47:22 +01:00
unwind Don't build in-tree llvm-libunwind if system-llvm-libunwind is enable 2021-01-09 12:50:08 +08:00