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[SR-11955] Cannot chain key path dynamic member subscripts #54375

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hamishknight opened this issue Dec 14, 2019 · 1 comment
Open

[SR-11955] Cannot chain key path dynamic member subscripts #54375

hamishknight opened this issue Dec 14, 2019 · 1 comment
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis

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@hamishknight
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Previous ID SR-11955
Radar rdar://problem/58435668
Original Reporter @hamishknight
Type Bug
Environment

Swift version 5.2-dev (Swift 7cdb285)
Target: x86_64-apple-darwin19.0.0

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

md5: 55ca75a77b438338ccb55a570c89d580

Issue Description:

We allow the chaining of key path dynamic members for a reference to a property, for example:

struct Q {
  var i = 0
}

@dynamicMemberLookup
struct R {
  subscript(dynamicMember kp: KeyPath<Q, Int>) -> Int { 0 }
}

@dynamicMemberLookup
struct S {
  subscript(dynamicMember kp: KeyPath<R, Int>) -> Int { 0 }
}

func foo(_ x: S) {
  _ = x.i
}

However we don't appear to be able to the same for subscripts:

struct Q {
  subscript(_ x: Int) -> Int { 0 }
}

@dynamicMemberLookup
struct R {
  subscript(dynamicMember kp: KeyPath<Q, Int>) -> Int { 0 }
}

@dynamicMemberLookup
struct S {
  subscript(dynamicMember kp: KeyPath<R, Int>) -> Int { 0 }
}

func foo(_ x: S) {
  _ = x[0] // error: Cannot convert value of type 'Int' to expected argument type 'KeyPath<R, Int>'
}
@beccadax
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@swift-ci create

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis
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@beccadax @hamishknight