cool,, as for UnsafeMutableRawBufferPointer.copy(from:bytes:), I cannot find such a function anywhere in the API. There is copyBytes(from:) <https://developer.apple.com/documentation/swift/unsafemutablerawbufferpointer/2635415-copybytes>, but the documentation is messed up and mentions a nonexistent count: argument over and over again. The documentation also doesn’t mention what happens if there is a length mismatch, so users are effectively relying on an implementation detail. I don’t know how to best resolve this.
On Tue, Aug 8, 2017 at 11:33 PM, Andrew Trick <atr...@apple.com> wrote: > > On Aug 8, 2017, at 8:29 PM, Taylor Swift <kelvin1...@gmail.com> wrote: > > > > On Tue, Aug 8, 2017 at 11:24 PM, Andrew Trick <atr...@apple.com> wrote: > >> >> 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> 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 >>> >>> >> 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. >> >> -Andy >> > > oh lol I was talking about assuming the pointer returned by > allocate(bytes:alignedTo:) is a multiple of alignedTo. Some code might be > relying on the last few bits of the pointer being zero; i.e. sticking bit > flags there like how some implementations store the red/black color > information in a red-black tree node. > > > Oh, sure. But I think it will be easy to fix the runtime. We could > probably do it before the proposal is accepted if necessary. > -Andy > >
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