> On Dec 15, 2015, at 6:39 PM, Dave Abrahams via swift-dev
> <swift-dev@swift.org> wrote:
>
>
>> On Dec 15, 2015, at 6:33 PM, Kevin Ballard via swift-dev
>> <swift-dev@swift.org> wrote:
>>
>> On Tue, Dec 15, 2015, at 03:03 PM, Joe Groff via swift-dev wrote:
>>>
>>> Yeah, it seems to me like a reasonable refinement for 'withUnsafePointer'
>>> to take an immutable parameter. Since this is a stdlib API change, you
>>> should suggest that on swift-evolution.
>>
>> A change like that is going to break any code that relies on the inout
>> optimization (where it uses call-by-reference instead of copy-in copy-out
>> when possible). Yes, such code is in violation of Swift semantics today, but
>> it does work.
>
> Two questions:
>
> 1. Don’t we want a withUnsafeMutablePointer for the mutating cases (where the
> inout optimization can take effect) anyway?
Yeah, a withUnsafeMutablePointer variant that is inout would be necessary.
> 2. Joe, these APIs predate many of your changes that make &x transparently
> convert to Unsafe[Mutable]Pointer arguments. Are they obsolete? Can we
> replace them with { x: Unsafe[Mutable]Pointer in … }(&y) ?
Not if you need the same pointer across multiple calls, or you need to convert
or adjust the pointer before the call. A call like foo(&x) that involves a
pointer conversion only guarantees that pointer for that exact call, as if
you'd written withUnsafe[Mutable]Pointer(&x) { foo($0) }.
-Joe
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