[swift-evolution] [Review] SE-0107: UnsafeRawPointer API (binding memory to type)

Andrew Trick atrick at apple.com
Sun Jul 10 08:41:55 CDT 2016

> On Jul 4, 2016, at 5:32 PM, Andrew Trick via swift-evolution <swift-evolution at swift.org> wrote:
>> On Jun 28, 2016, at 11:05 PM, Chris Lattner <clattner at apple.com <mailto:clattner at apple.com>> wrote:
>> Hello Swift community,
>> The review of “SE-0107: UnsafeRawPointer API” begins now and runs through July 4, 2016. The proposal is available here:
>> 	https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md <https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md>

I'm revising this proposal based on last week's feedback. A few of the
additive APIs are removed and a number of UnsafePointer and
UnsafeRawPointer methods are renamed.

Here is a PR for the revision. Note that the examples in the proposal
text still need to be updated:

I updated the short-form summary of the API:

The full UnsafeRawPointer API with doc comments is here:

The UnsafePointer and UnsafeRawPointer changes are on this branch:

If you wish to comment line-by-line on the detailed docs or
implementation, you can do so here:

I should preemptively answer the question "why do UnsafeRawPointer
methods take an explicit type argument when it can be inferred?". Such

  rawPtr.initializeMemory(as: Int.self, ...)

These methods don't simply operate on values of some type, they
actively bind memory to that type. At the point of use, that type
needs to be explicit to convey that fact. It's important for
readability, comprehension, and correctness. We cannot rely on type
inferrence on some expression which can change without the original
author's intervention resulting in subtle miscompiles.

The only concern I have about this version of the proposal is this method name: 

  func copyBytes(from: UnsafeRawPointer, count: Int)

because `count` usually refers to a number of values. I think it should be:

  func copy(bytes: Int, from: UnsafeRawPointer)


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