Over-aligned Vec<u8> can potentially be converted into Vec<u16> without violating the requirement of dealloc with the correct alignment by a layout-changing realloc
This would probably take the shape of unsafe fn grow(&self, ptr: *mut u8, old_layout: Layout, new_layout: Layout) -> *mut u8 { ... } and shrink for GlobalAlloc along with the plumbing to see that through. These should probably be defaulted to call realloc where possible to avoid pessimization of old GlobalAlloc implementers.
Alternatively to providing the grow/shrink split on GlobalAlloc, some alternative symbol to realloc could be used which still allows both grow and shrink. C-inspired bad idea: realloc_s 😛 but resize might be fine. realloc will still exist (maybe deprecated) to point at resize as the improved alternative.
This is a short-term potentially stabilizable incremental improvement on the status quo.
Zulip discussion
There's at least two benefits to doing this:
reallocthat takesLayoutwill allow it to benefit from https://github.com/rust-lang/rust/pull/95295Vec<u8>can potentially be converted intoVec<u16>without violating the requirement of dealloc with the correct alignment by a layout-changingreallocThis would probably take the shape of
unsafe fn grow(&self, ptr: *mut u8, old_layout: Layout, new_layout: Layout) -> *mut u8 { ... }andshrinkforGlobalAllocalong with the plumbing to see that through. These should probably be defaulted to callreallocwhere possible to avoid pessimization of oldGlobalAllocimplementers.Alternatively to providing the
grow/shrinksplit onGlobalAlloc, some alternative symbol torealloccould be used which still allows both grow and shrink. C-inspired bad idea:realloc_s😛 butresizemight be fine.reallocwill still exist (maybe deprecated) to point atresizeas the improved alternative.