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

[Andrew Trick]

> On Jul 11, 2016, at 10:22 AM, Dave Abrahams <dabrahams at apple.com> wrote:
> 
> 
> on Mon Jul 11 2016, Andrew Trick <atrick-AT-apple.com <http://atrick-at-apple.com/>> wrote:
> 
>>> On Jul 11, 2016, at 12:50 AM, Ben Rimmington <me at benrimmington.com> wrote:
>>> 
>>> 
>>>> On 10 Jul 2016, at 14:41, Andrew Trick via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>> 
>>>> 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:
>>>> https://github.com/apple/swift-evolution/pull/420
>>>> 
>>>> I updated the short-form summary of the API:
>>>> https://github.com/atrick/swift-evolution/blob/3122ace9d2fb55072ebd7395c7353fcbf497318a/proposals/0107-unsaferawpointer.md#full-unsaferawpointer-api
>>>> 
>>>> The full UnsafeRawPointer API with doc comments is here:
>>>> https://github.com/atrick/swift/blob/22e3a2885e4236888ec447a7148acf633d8544f5/stdlib/public/core/UnsafeRawPointer.swift.gyb
>>>> 
>>>> The UnsafePointer and UnsafeRawPointer changes are on this branch:
>>>> https://github.com/atrick/swift/commits/rawptr
>>>> 
>>>> If you wish to comment line-by-line on the detailed docs or
>>>> implementation, you can do so here:
>>>> https://github.com/apple/swift/pull/3437
>>>> 
>>>> ---
>>>> 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)
>>> 
>>> Using `bytes` to label the count / length / size would be inconsistent with:
>>> 
>>> 	Foundation.Data.init(bytes:count:)
>>> 	<https://developer.apple.com/reference/foundation/data/1780158-init>
>>> 
>>> 	Foundation.Data.copyBytes(to:count:)
>>> 	<https://developer.apple.com/reference/foundation/data/1780297-copybytes>
>>> 
>>> UnsafeMutableRawPointer could use a `size` or `sizeInBytes` label.
>>> (This also applies to the `allocate` and `deallocate` methods).
>>> 
>>> — Ben
>> 
>> Thanks for pointing that out.
>> 
>> My concern is code like:
>> 
>>  let ptrToInt: UnsafePointer<Int32> = …
>>  rawPtr.copyBytes(from: ptrToInt, count: 4)
>> 
>> which looks a lot like 4 Int32s will be copied when only 1 Int32 will actually be copied.
>> 
>> Anyone care to vote on this?
> 
> I think you're being overly fussy.  The name clearly says we're copying
> bytes.  count says how many.  But if you want to avoid any possibility
> of confusion, only support source pointers that are UnsafeRawPointer.


Thanks. I’ll take that as a +1 for the current form.

We support implicit argument conversion from UnsafePointer<T> to UnsafeRawPointer primarily so that UnsafePointers can be passed as `void*` arguments.

-Andy

>> 
>> 
>> Current:
>> 
>>  let rawPtr = UnsafeMutableRawPointer.allocate(bytes: 24)
>>  rawPtr.copyBytes(from: ptrToInt, count: 24)
>>  rawPtr.deallocate(bytes: 24)
>> 
>> Proposed:
>> 
>>  let rawPtr = UnsafeMutableRawPointer.allocate(sizeInBytes: 24)
>>  rawPtr.copyBytes(from: ptrToInt, sizeInBytes: 24)
>>  rawPtr.deallocate(sizeInBytes: 24)
>> 
>> -Andy
> 
> -- 
> Dave

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