Support uninitialized elements in .assign() and .fill() #798
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The trick is simply to traverse the target array using a raw view / raw pointers; this means we don't create any references to potentially-uninitialized values. Assignment `*x = y.clone()` is used where x is a *mut A, y is a &A; this will work as intended when A: Copy; assignment should not need that the value being overwritten, when Copy, is initialized. Unfortunately we use Zip here instead of the older methods (zip_mut_with, unordered_foreach_mut); because Zip implemnets equivalent functionality but in a generic way. The access pattern and performance is not guaranteed to be identical.
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Benchmarks suggest .fill() is unchanged. Looks like we don't have an assign benchmark. |
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Source to back us up on that assignment through |
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Thoughts for next time: Rethink - we introduced |
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The trick is simply to traverse the target array using a raw view / raw
pointers; this means we don't create any references to
potentially-uninitialized values.
Assignment
*x = y.clone()is used where x is a *mut A, y is a &A;this will work as intended when A: Copy; assignment should not need that
the value being overwritten, when Copy, is initialized.
Unfortunately we use Zip here instead of the older methods
(zip_mut_with, unordered_foreach_mut); because Zip implements equivalent
functionality but in a generic way. The access pattern and performance
is not guaranteed to be identical.
Related to issue #685