[swift-evolution] Question about heterogeneous collections

Jason Sadler jason.sadler at gmail.com
Wed Mar 30 12:11:53 CDT 2016

Hi folks,

I have an issue with using a heterogeneous array of objects conforming to a
protocol - I want to write an extension on Array (or CollectionType) that
applies only when Element : MyProtocol, but I can’t call methods in that
extension from an instance of [MyProtocol] because "Using ‘MyProtocol' as a
concrete type conforming to protocol ‘MyProtocol' is not supported”

(For more background, my full use case can be seen in this gist:

I’ve asked about this on swift-users (
and got some good workarounds but no one was able to provide me with
information on any future plans in swift to address this issue - whether
that’s making protocols conform to themselves, or some other improved
approach to heterogeneous collections. I wonder if anyone here can shed
some light on this? (I’m new to the mailing lists, sorry!)

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