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[SR-9501] Subclass existential with predefined associated type witness should be supported as existential #51955

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AnthonyLatsis opened this issue Dec 13, 2018 · 1 comment
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[SR-9501] Subclass existential with predefined associated type witness should be supported as existential #51955

AnthonyLatsis opened this issue Dec 13, 2018 · 1 comment
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compiler The Swift compiler in itself duplicate Resolution: Duplicates another issue existentials Feature: values of types like `any Collection`, `Any` and `AnyObject`; type-erased values feature A feature request or implementation improvement swift evolution implemented Flag → feature: A feature that was approved through the Swift evolution process and implemented type checker Area → compiler: Semantic analysis

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@AnthonyLatsis
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AnthonyLatsis commented Dec 13, 2018 •
edited

Previous ID SR-9501
Radar None
Original Reporter @AnthonyLatsis
Type Bug
Status Resolved
Resolution Duplicate
Environment

Xcode 10.1 (10B61) & master

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

md5: 075e0f26634a1fe1f91a9305b41c2dac

duplicates:

  • SR-4758 SE-0142: derived protocol that restricts associatedtype should be allowed as a variable type

Issue Description:

This is a variation of SR-4758 that I believe should be faced separately. Here, the associated type is known to be concrete through a type alias in the class component of a subclass existential (rather than through where clauses on protocol declarations that directly constraint an assoc. type).

class Class {
  typealias Assoc = Int
}
protocol Proto {
    associatedtype Assoc
}

func foo(arg: Class & Proto) {} // protocol 'Proto' can only be used as a generic constraint because it has Self or associated type requirements.
@belkadan
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belkadan commented Dec 13, 2018 •
edited by AnthonyLatsis

This doesn't work today, but it probably should:

class Class {
  typealias Assoc = Int
}
protocol Proto {
  associatedtype Assoc
}
class Sub: Class, Proto {
  typealias Assoc = String // shadows Class.Assoc
}

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@AnthonyLatsis AnthonyLatsis added duplicate Resolution: Duplicates another issue improvement type checker Area → compiler: Semantic analysis swift evolution implemented Flag → feature: A feature that was approved through the Swift evolution process and implemented existentials Feature: values of types like `any Collection`, `Any` and `AnyObject`; type-erased values feature A feature request or implementation and removed bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. labels Jan 28, 2023
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Labels
compiler The Swift compiler in itself duplicate Resolution: Duplicates another issue existentials Feature: values of types like `any Collection`, `Any` and `AnyObject`; type-erased values feature A feature request or implementation improvement swift evolution implemented Flag → feature: A feature that was approved through the Swift evolution process and implemented type checker Area → compiler: Semantic analysis
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@belkadan @AnthonyLatsis