Refactor unsafe implementation of std::mem::replace #117189
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The function now defers to mem::swap, which both eliminates the use of `unsafe` in the function, and also allows it (and mem::take) to benefit from any performance enhancements to mem::swap, such as the current use of ptr::swap_nonoverlapping for large types.
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| The Miri subtree was changed cc @rust-lang/miri |
| Seems that there are more performance implications than I expected, as evidenced by the failure of |
| } | ||
| pub const fn replace<T>(dest: &mut T, mut src: T) -> T { | ||
| swap(dest, &mut src); | ||
| src |
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You were essentially trying to revert #83022 here.
Maybe we should have a comment explaining why this is not calling swap?
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I think a comment is a good idea. It's not immediately clear that swap was being avoided for performance reasons.
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Do you want to make a PR for that? :)
…t, r=thomcc Explain implementation of mem::replace This adds a comment to explain why `mem::replace` is not implemented in terms of `mem::swap` to prevent [naïfs like me](rust-lang#117189) from trying to "fix" it.
Rollup merge of rust-lang#117243 - chfogelman:replace-not-swap-comment, r=thomcc Explain implementation of mem::replace This adds a comment to explain why `mem::replace` is not implemented in terms of `mem::swap` to prevent [naïfs like me](rust-lang#117189) from trying to "fix" it.
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The function now defers to mem::swap, which both eliminates the use of
unsafein the function, and also allows it (and mem::take) to benefit from any performance enhancements to mem::swap, such as the current use of ptr::swap_nonoverlapping for large types.