[swift-evolution] Unmanaged, and COpaquePointer vs. Unsafe(Mutable)Pointer

[John McCall]

> On Dec 8, 2015, at 12:26 AM, Jacob Bandes-Storch via swift-evolution <swift-evolution at swift.org> wrote:
> One hopes to avoid COpaquePointer and Unsafe(Mutable)Pointer, but in practice I've had occasion to use them a few times.
> 
> Things that are nice:
> 
> - Unmanaged.passUnretained/takeRetained/etc. which make memory management semantics explicit.
> 
> Things I've been frustrated by:
> 
> - An API takes UnsafeMutablePointer<Void>, but Unmanaged.toOpaque() returns a COpaquePointer.
> 
> - An API gives me UnsafeMutablePointer<Void>, but Unmanaged.fromOpaque() takes a COpaquePointer.
> 
> 
> In practice, I end up with monstrosities like:
> 
> Unmanaged.passRetained(CFCopyDescription(Unmanaged<AnyObject>.fromOpaque(COpaquePointer($0)).takeUnretainedValue()))
> 
> 
> I think a few things could help:
> 
> - Phase out COpaquePointer in favor of UnsafePointer<Void> (is this already happening?)

I think this is planned, but it would be good to verify that.  We should definitely be consistent about which type we’re using.

> - Add implicit conversion from COpaquePointer to Unsafe(Mutable)Pointer<Void>, and/or vice versa.
> 
> - Even better, add implicit conversion from Unmanaged<T> to COpaquePointer or UnsafePointer<Void>, behaving the way toOpaque() currently does. Also, replace Unmanaged.fromOpaque() with an initializer Unmanaged(_: UnsafePointer<Void>).

We try very hard to avoid adding new implicit conversions.

John.
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