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

[Joe Groff]

COpaquePointer is IMO a vestige that should be eliminated completely. We'd ultimately like to import opaque C structs as distinct, non-constructible types in Swift, so that they can still be well-typed UnsafePointer<OpaqueThing> types in Swift.

-Joe

> 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?)
> 
> - 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>).
> 
> 
> What are others' experiences? Would it be feasible/favorable to have some of these conversions?
> 
> Jacob Bandes-Storch
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