> On Aug 8, 2017, at 6:51 PM, Taylor Swift <kelvin1...@gmail.com> wrote:
> On Tue, Aug 8, 2017 at 9:38 PM, Andrew Trick <atr...@apple.com 
> <mailto:atr...@apple.com>> wrote:
>> > UnsafeMutableRawBufferPointer.allocate(bytes:alignedTo:)
>> Well, I think it's somewhat ridiculous for users to write this every time 
>> they allocate a buffer:
>> `UnsafeMutableRawBufferPointer.allocate(bytes: size, alignedTo: 
>> MemoryLayout<UInt>.alignment)`
>> If anyone reading the code is unsure about the Swift API's alignment
>> guarantee, it's trivial to check the API docs.
>> You could introduce a clearly documented default `alignedTo`
>> argument. The reason I didn't do that is that the runtime won't
>> respect it anyway. But I think it would be fair to go ahead with the
>> API and file a bug against the runtime.
>> Default argument of MemoryLayout<Int>.alignment is the way to go but as you 
>> said i don’t know if that is actually allowed/works. An alternative is to 
>> have two allocate methods each, one that takes an alignment argument and one 
>> that doesn’t (and aligns to pointer alignment) but that feels inelegant. 
>> Default arguments would be better.
> Default argument makes sense to me too. Then the raw buffer pointer and 
> regular raw pointer APIs can be consistent with each other.
> Runtime bug: https://bugs.swift.org/browse/SR-5664 
> <https://bugs.swift.org/browse/SR-5664>
> yikes i was not aware of this. I don’t think it’s bad enough to warrant 
> dropping the argument like with deallocate(capacity:) but I can imagine bad 
> things happening to code that crams extra inhabitants into pointers.

If we ever need to do pointer adjustment during deallocation to accommodate 
alignment, then I think the Swift runtime can track that. I see no reason to 
muddy the UnsafeRawPointer API with it. So, I agree with your proposed change 
to drop `alignedTo` there.

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