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

Andrew Trick atrick at apple.com
Sat Sep 2 16:41:57 CDT 2017

> On Sep 2, 2017, at 2:06 PM, Taylor Swift via swift-evolution <swift-evolution at swift.org> wrote:
> the subscript doesn’t know about the stride that you want to use. If you want to get rid of the `at:` ambiguity, you have to get rid of it everywhere, or users will just wind up having to remember two ways (one ambiguous and one less ambiguous) of doing the same thing, instead of one (ambiguous) way of doing it.
> Certainly, that's a good point. On rethink and another re-reading of the proposal, it's unclear to me that the addition of `at` arguments to UnsafeMutablePointer is sufficiently justified by the proposal text. Is it merely that it's shorter than writing `foo + MemoryLayout<T>.stride * offset`? With the ambiguity of `at`, it seems that the current way of writing it, though longer, is certainly less ambiguous. 
> Please reread it; UnsafeMutablePointer’s methods do not use `at:`.

Regarding the typed buffer pointers, I think it is clear by convention, and will be well documented, that the `at` label refers to a position in `self`.

The raw buffer pointer API isn’t so obvious. Since the `at` refers to `self` it might more logically be a byte offset. Note that `at` as a label name always refers to a strided index.

This would be a bit more explicit:
UnsafeRawBufferPointer.initializeMemory(as:T.self, atByteOffset: position * MemoryLayout<T>.stride, from: bufferOfT)

But possibly less convenient… Since that `at` label currently on UnsafeRawPointer.initializeMemory is almost never used, I don’t think we need to worry too much about convenience.

That existing `at` label on UnsafeRawPointer.initializeMemory, would also need to be renamed, which is fine.

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