[swift-evolution] [Review] SE-0156: Class and Subtype existentials

Adrian Zubarev adrian.zubarev at devandartist.com
Wed Mar 1 01:56:42 CST 2017

1) What is your evaluation of the proposal?

This is a critical must have feature in Swift. I’ve been waiting for it since Swift 1.2.

2) Is the problem being addressed significant enough to warrant a change to Swift?


3) Does this proposal fit well with the feel and direction of Swift?

No doubt.

4) If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?

Yes in Objective-C. This proposal does not add the where clause to existentials yet, but it leaves the door open to add that in the future, which would make the feature even more powerful.

5) How much effort did you put into your review? A glance, a quick reading, or an in-depth study?

I originally pitched the idea of class existentials calling them type<A,B> compared to the old style protocol<A,B> in 2016. Then I tracked every topic about existentials on the mailing list. And I carefully read every pitch and proposal including existentials.

Adrian Zubarev
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