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

[Jacob Bandes-Storch]

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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