Be more precise about array cookies #123
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Per discussion with @zygoloid, the standard does not permit cookie alignment to be factored into allocations, either by changing the resolution of operator new[] or changing the `std::align_val_t` argument. We could ask for this to be changed, but it's not clear that there's any reasonable solution for class-specific allocators that don't take an explicit alignment, which it seems reasonable to say should be allowed to return something based on the alignment of the class. Given that, the only reasonable decision is to not always align the cookie. We should still be able to assume it's aligned in common cases.
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I've updated the PR per an offline conversation with @zygoloid. The standard does not appear to permit cookie alignment to be factored into allocations, either by changing the resolution of operator new[] or changing the Implementations should still be able to assume the cookie is aligned in common cases. I will leave this open for this rest of this week for review. |
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
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Is there any need to discuss this with WG21's CWG? |
My understanding is that Richard asked the reflector about it a few years ago and didn't get any response. If the committee decides in the future that implementations can/should upgrade the alignment of array allocations, it's mostly non-ABI-breaking for us to start doing that. The only concern would be what alignment we can assume in |
Addresses issue #119.