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[SR-6473] Generic subscripts don't work as protocol requirements #49023

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lattner mannequin opened this issue Nov 25, 2017 · 3 comments
Closed

[SR-6473] Generic subscripts don't work as protocol requirements #49023

lattner mannequin opened this issue Nov 25, 2017 · 3 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself

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@lattner
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Mannequin

lattner mannequin commented Nov 25, 2017

Previous ID SR-6473
Radar None
Original Reporter @lattner
Type Bug
Status Resolved
Resolution Invalid
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: edcc85d2bd744a54b39f3b6c82f8aef2

Issue Description:

I'd really like for this to be possible:

public protocol P1 {
subscript<T2> () -> T2 { get }
}
struct Impl : P1 {
subscript() -> Int {
return 42
}
}

we currently reject it incorrectly like this:

t.swift:49:8: error: type 'Impl' does not conform to protocol 'P1'
struct Impl : P1 {
^
t.swift:50:3: note: candidate has non-matching type '() -> Int'
subscript() -> Int {
^
t.swift:46:3: note: protocol requires subscript with type '<T2> () -> T2'; do you want to add a stub?
subscript<T2> () -> T2 { get }
^
@lattner
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Mannequin Author

lattner mannequin commented Nov 25, 2017

@slavapestov, @DougGregor, is this a shallow bug or something really deep?

-Chris

@DougGregor
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The example as written is ill-formed, because Impl’s subscript needs to be generic as well. If generic subscripts are actually broken in protocols, I’d expect the bug to be shallow.

@slavapestov
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This works:

public protocol P1 {
  subscript<T2> (t: T2) -> T2 { get }
}

struct Impl : P1 {
  subscript<T2>(t: T2) -> T2 { return t }
}

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself
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@slavapestov @DougGregor