[swift-evolution] [swift-evolution-announce] [Review] SE-0017: Change Unmanaged to use UnsafePointer

[Andrew Trick]

> On Apr 28, 2016, at 11:10 AM, Chris Lattner <clattner at apple.com> wrote:
> 
> Hello Swift community,
> 
> The review of "SE-0017: Change Unmanaged to use UnsafePointer" begins now and runs through May 3. The proposal is available here:
> 
> 	https://github.com/apple/swift-evolution/blob/master/proposals/0017-convert-unmanaged-to-use-unsafepointer.md


I have some concerns, but let me just suggest a simple alternative and see what people think...

- Leave the existing from/toOpaque API until we can come up with a better plan for moving away from OpaquePointer.

- Add initializers to avoid boilerplate, but only for "safe" variants of the cast:

extension Unmanaged {
  @_transparent
  public init(_ from : UnsafePointer<Instance>)

  @_transparent
  public init?(_ from : UnsafePointer<Instance>?)
}

extension UnsafeMutablePointer where Pointee : AnyObject {
  @_transparent
  public init(_ from : Unmanaged<Pointee>)

  @_transparent
  public init?(_ from : Unmanaged<Pointee>?)
}

- This doesn't solve the stated problem of passing unmanaged pointers to 'void*' imports. Is that really an issue? I believe the correct fix is to stop importing 'void*' as UnsafePointer<Void>. We should have a nominally distinct "opaque" pointer type, 'void*' should be imported as that type, and casting from any UnsafePointer to the opaque pointer type should be inferred and implicit for function arguments. I can send a proposal for eliminating UnsafePointer<Void> next week, but the scope of that proposal will be much broader.

-Andy