rust/library/core
bors 46a934a1dc Auto merge of #83022 - m-ou-se:mem-replace-no-swap, r=nagisa
Don't implement mem::replace with mem::swap.

`swap` is a complicated operation, so this changes the implementation of `replace` to use `read` and `write` instead.

See https://github.com/rust-lang/rust/pull/83019.

I wrote there:

> Implementing the simpler operation (replace) with the much more complicated operation (swap) doesn't make a whole lot of sense. `replace` is just read+write, and the primitive for moving out of a `&mut`. `swap` is for doing that to *two* `&mut` at the same time, which is both more niche and more complicated (as shown by `swap_nonoverlapping_bytes`).

This could be especially interesting for `Option<VeryLargeStruct>::take()`, since swapping such a large structure with `swap_nonoverlapping_bytes` is going to be much less efficient than `ptr::write()`'ing a `None`.

But also for small values where `swap` just reads/writes using temporary variable, this makes a `replace` or `take` operation simpler:
![image](https://user-images.githubusercontent.com/783247/110839393-c7e6bd80-82a3-11eb-97b7-28acb14deffd.png)
2021-03-12 23:27:23 +00:00
..
benches Auto merge of #74024 - Folyd:master, r=m-ou-se 2021-03-05 20:12:13 +00:00
src Auto merge of #83022 - m-ou-se:mem-replace-no-swap, r=nagisa 2021-03-12 23:27:23 +00:00
tests Rollup merge of #79208 - LeSeulArtichaut:stable-unsafe_op_in_unsafe_fn, r=nikomatsakis 2021-03-10 08:01:25 +09:00
Cargo.toml