> On Dec 16, 2015, at 11:59 AM, Kevin Ballard <ke...@sb.org> wrote:
>
> On Wed, Dec 16, 2015, at 11:49 AM, Joe Groff wrote:
>>
>>> On Dec 16, 2015, at 11:47 AM, Kevin Ballard <ke...@sb.org
>>> <mailto:ke...@sb.org>> wrote:
>>>
>>> On Wed, Dec 16, 2015, at 11:42 AM, Joe Groff wrote:
>>>>
>>>>> On Dec 16, 2015, at 11:24 AM, Kevin Ballard via swift-dev
>>>>> <swift-dev@swift.org <mailto:swift-dev@swift.org>> wrote:
>>>>>
>>>>> On Wed, Dec 16, 2015, at 12:12 AM, Dave Abrahams wrote:
>>>>>>
>>>>>>> Come to think of it, what's the actual use-case for withUnsafePointer()?
>>>>>>
>>>>>> I'm not sure we still have one that isn't covered by &x; that's my point.
>>>>>>
>>>>>>> If a value is mutable, you can already use &x or
>>>>>>> withUnsafeMutablePointer(), and if it's immutable, you can't call
>>>>>>> withUnsafePointer() today anyway. The proposed change would just make
>>>>>>> withUnsafePointer() into the equivalent of `var x = value;
>>>>>>> callSomethingWith(&x)`. The only reason to really want a
>>>>>>> withUnsafePointer() function is if it can give you an UnsafePointer to
>>>>>>> an immutable value without copying it, but we can't do that. I'm
>>>>>>> inclined to say we should just get rid of withUnsafePointer() entirely,
>>>>>>> at least until such time as Swift has a way to pass immutable values
>>>>>>> by-ref.
>>>>>>
>>>>>> I'm inclined to agree. Proposal?
>>>>>
>>>>> Sure, I'll write one up. I suspect that withUnsafePointer() /
>>>>> withUnsafeMutablePointer() are likely to be rarely used today, and most
>>>>> uses can probably be trivially replaced with just passing a &x ref, so
>>>>> this shouldn't be a big deal.
>>>>
>>>> We can't remove withUnsafe[Mutable]Pointer; as I mentioned to Dave, it's
>>>> necessary to persist a pointer for more than one immediate call.
>>>
>>> Rare cases like that can be covered by either declaring a nested function
>>> taking the pointer and calling it, calling an anonymous local closure of
>>> the right type, or even using withExtendedLifetime(&x) { (ptr:
>>> UnsafePointer<T>) in ... }.
>>
>> These are all just withUnsafePointer with different spelling.
>
> That's true, but they all have the benefit of not requiring extra stdlib
> functions. swiftdoc.org lists 36 global functions, a full 4 of which are
> withUnsafePointer + variants. The existence of the functions also implies
> that they're necessary to work with pointers (especially the documentation).
> My suspicion is that nearly all current uses of these functions can be
> replaced with &x refs with no change in functionality. Even the stdlib only
> has a handful of uses of withUnsafeMutablePointer (and none at all for
> withUnsafePointer), and looking through them quickly, it looks like only the
> ones in public/core/Runtime.swift.gyb require a workaround.
>
The standard library isn't a representative sample, since it doesn't interact
directly with that much C code. I would check out Github for more information;
I've had a number of discussions with developers who were doing things that are
only possible with withUnsafePointer.
-Joe
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