[swift-evolution] [swift-evolution-announce] [Review] SE-0184: Unsafe[Mutable][Raw][Buffer]Pointer: add missing methods, adjust existing labels for clarity, and remove deallocation size

Jean-Daniel mailing at xenonium.com
Sat Sep 9 05:15:39 CDT 2017

> Le 8 sept. 2017 à 03:03, Andrew Trick via swift-evolution <swift-evolution at swift.org> a écrit :
>> On Sep 7, 2017, at 5:37 PM, Joe Groff <jgroff at apple.com> wrote:
>>> The important thing is that the UnsafeBufferPointer API is clearly documented. We do not want users to think it’s ok to deallocate a smaller buffer than they allocated.
>>> Unfortunately, there’s actually no way to assert this in the runtime because malloc_size could be larger than the allocated capacity. Incorrect code could happen to work and we can live with that.
>> Would it be sufficient to assert that malloc_good_size(passedCapacity) == malloc_size(base) ? It wouldn't be perfect but could still catch a lot of misuses.
> That theory does hold up for a million random values, but I don’t know if we can rely on malloc_size never being larger than roundUp(sz, 16). Greg?

You can’t. This may be true while alloc size if less than a page, but a quick test show that:

malloc_size(malloc(4097)) = 4608

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