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

[Taylor Swift]

https://github.com/apple/swift-evolution/pull/750
https://github.com/apple/swift/pull/12200

On Sat, Sep 30, 2017 at 2:15 AM, Taylor Swift <kelvin13ma at gmail.com> wrote:

>
>
> On Thu, Sep 28, 2017 at 7:59 PM, Andrew Trick <atrick at apple.com> wrote:
>
>>
>> On Sep 6, 2017, at 10:15 PM, Taylor Swift <kelvin13ma at gmail.com> wrote:
>>
>> okay so I think so far what’s been agreed on is
>>
>> *1*. rename “Bytes” to “Memory” in the raw pointer API. Note: this
>> brings the `copyBytes<C>(from:)` collection method into the scope of
>> this proposal
>>
>> *2*. change raw offsets to be in terms of bytes, not typed strides. This
>> argument will be called `atByteOffset:` and will only appear in
>> UnsafeMutableRawBufferPointer. “at:” arguments are no longer needed in
>> UnsafeMutableRawPointer, since we can just use pointer arithmetic now.
>>
>>
>> *3*. move UnsafeMutableBufferPointer’s `at:` arguments to the front of
>> the parameter list. mostly cause any pointer arithmetic happens in the
>> front so structurally we want to mirror that.
>>
>> *4*. add dual (to:) single element initializers and assigners to
>> UnsafeMutablePointer, but not UnsafeMutableRawPointer because it’s
>> apparently not useful there. `UnsafeMutableRawPointer.initi
>> alizeMemory<T>(as:repeating:count:)` still loses its default count to
>> prevent confusion with its buffer variant.
>>
>> *5*. memory deallocation on buffer pointers is clearly documented to
>> only be defined behavior when the buffer matches a whole heap block.
>>
>>
>> Kelvin,
>>
>> Attempting to limit the scope of this proposal backfired. I was hoping to
>> avoid discussing changes to the slice API, instead providing basic
>> functionality within the buffer API itself. However, Dave Abrahams has
>> argued that once the slice API is extended, the positional arguments are
>> extraneous and less clear.
>>
>> Instead of
>>
>>   buf.intialize(at: i, from: source)
>>
>> We want to force a more obvious idiom:
>>
>>   buf[i..<n].intialize(from: source)
>>
>> I think this is a reasonable argument and convinced myself that it's
>> possible to extend the slice API. I'm also convinced now that we don't need
>> overloads to handle an UnsafeBufferPointer source, instead we can provide a
>> single generic entry point on both UnsafeMutableBufferPointer and its
>> slice, optimized within the implementation:
>>
>>  `initialize<S : Sequence>(from: S) -> (S.Iterator, Index)
>>
>> We can always drop down to the UnsafePointer API to get back to a direct
>> unsafe implementation as a temporary workaround for performance issues.
>>
>> Let's set aside for now whether we support full or partial
>> initialization/assignment, how to handle moveInitialize, and whether we
>> need to return the Iterator/Index. This is going to require another
>> iteration on swift-evolution, which *we should discuss in a separate
>> thread*.
>>
>> At this point, I suggest removing the controversial aspects of SE-0184 so
>> that we can put the other changes behind us and focus future discussion
>> around a smaller follow-up proposal.
>>
>> Here I've summarized the changes that I think could be accepted as-is:
>> https://gist.github.com/atrick/c1ed7afb598e5cc943bdac7683914e3e
>>
>> If you amend SE-0184 accordingly and file a new PR, I think it can be
>> quickly approved.
>>
>> -Andy
>>
>>
> Part one of SE-0184 is here as SE-0184 A
> <https://github.com/kelvin13/swift-evolution/blob/improved-pointers/proposals/0184a-unsafe-pointers-part-1.md>
> I’ll implement it tomorrow and then make the PR
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170930/ab9ebd80/attachment.html>