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[SR-5341] Protocol with associatedtype constrained to another protocol & inheritance does not compile #47915

swift-ci opened this issue Jun 30, 2017 · 4 comments


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@swift-ci swift-ci commented Jun 30, 2017

Previous ID SR-5341
Radar None
Original Reporter nosyjoe (JIRA User)
Type Bug
Status Resolved
Resolution Duplicate

Apple Swift version 3.1 (swiftlang-802.0.53 clang-802.0.42) on macOS Sierra 10.12.5

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: 8c4e951fe2798e81b8c0c71c8419931f


  • SR-55 non-@objc protocol existentials do not conform to their own protocol type

Issue Description:

Given the following three protocol and one class:

protocol View { }

protocol ExtendedView: View {
    func foo()

protocol Presenter {
    associatedtype ConcreteView: View
    func attach(view: ConcreteView)

class APresenter: Presenter {
    typealias ConcreteView = ExtendedView
    func attach(view: ExtendedView) { }

the compiler produces the following error:

{{Error🙁25, 7) type 'APresenter' does not conform to protocol }}'Presenter'

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@belkadan belkadan commented Jul 1, 2017

This is correct-ish behavior, in that a protocol value does not count as a type that conforms to the protocol. @jckarter, is there a particular SR we're tracking this under?

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Collaborator Author

@swift-ci swift-ci commented Jul 4, 2017

Comment by Philipp Engel (JIRA)

Are you considering to change this? To me it makes sense and to have a protocol count as a conforming type.

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@jckarter jckarter commented Jul 5, 2017

Yeah, it's one facet of "generalized existentials" under Doug's generics manifesto. SR-55 looks like the canonical SR.

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Collaborator Author

@swift-ci swift-ci commented Jul 6, 2017

Comment by Philipp Engel (JIRA)

ok great thx guys! I'm going to check out the Generics Manifesto and follow the process of SR-55 from now on.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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