46a934a1dc
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:  |
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