[swift-users] experimental conditional conformances flag

[Matt Whiteside]

Thanks Jens.  Your example does work for me.  The use case I have been trying to accomplish is conditional conformance of a protocol, not a struct.  After re-reading, it looks like this is not covered by SE-0143.

import CoreGraphics

protocol Drawable {
  func draw()
}

protocol Point2D{
  associatedtype T:FloatingPoint & ExpressibleByFloatLiteral
  var x:T{
    get
  }
  var y:T{
    get
  }
}

extension Collection: Drawable where Element:Point2D {//error: Extension of protocol ‘Collection’ cannot have an inheritance clause
  func draw(){
    print("drawing something here")
  }
}

Matt


> On Dec 6, 2017, at 00:25, Jens Persson <jens at bitcycle.com> wrote:
> 
> Oh I forgot to include the step where I select the newly installed toolchain ...
> 
> On Wed, Dec 6, 2017 at 9:24 AM, Jens Persson via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
> I've now installed 2017-12-05 snapshot and can confirm that it too works for me.
> In more detail:
> 
> 1. Install swift-DEVELOPMENT-SNAPSHOT-2017-12-05-a-osx.pkg
> 
> 2. Restart Xcode (I'm using Xcode 9.2 (9C40b))
>     (I guess it shouldn't be necessary to restart, but I think it might be ...)
> 
> 3. Create a new command line project.
> 
> 4. Put -enable-experimental-conditional-conformances in Other Swift Flags in the project's Build Settings.
> 
> 5. Enter the following code in main.swift and Build (which works without errors):
> 
> protocol P {}
> struct S<T> {}
> extension S: P where T: P {}
> 
> 
> Regarding step 2. I'm not 100% sure, but I think that it might be necessary to restart Xcode after installing a new snapshot, because even if the new snapshot can be selected from the toolchains menu, it doesn't take affect until after restarting Xcode. I'm always restarting Xcode after installing and selecting a new toolchain. Someone please correct me if you can prove that this isn't necessary.
> 
> /Jens
> 
> On Wed, Dec 6, 2017 at 7:48 AM, Jens Persson via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
> It works for me with Xcode 9.1 and 9.2 using latest dev snapshot (from 2017-11-28 and 2017-12-03), I added -enable-experimental-conditional-conformances in Other Swift Flags as you show in the screenshot.
> /Jens
> 
> On Wed, Dec 6, 2017 at 4:32 AM, Matt Whiteside via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
> Hello Swift Users,
> 
> [This is a resend with smaller attachment]  Has anyone had luck passing the new '-enable-experimental-conditional-conformances' flag to Xcode?  It works when I run swift from the command line, with the Dec. 5th snapshot toolchain, but not Xcode.  I have tried whats in the screenshot below as well as adding -Xfrontend, but I’m still getting the usual ‘extension of protocol cannot have an inheritance clause’ error:
> 
> Thanks for any suggestions on this,
> 
> Matt
> 
> 
> <Screen Shot 2017-12-05 at 19.19.06.png>
> 
> 
> 
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