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[SR-12459] Cannot call equality operator declared as a static member of a protocol #54899

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ahoppen opened this issue Mar 31, 2020 · 5 comments
Closed

[SR-12459] Cannot call equality operator declared as a static member of a protocol #54899

ahoppen opened this issue Mar 31, 2020 · 5 comments
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@ahoppen
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis

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@ahoppen
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ahoppen commented Mar 31, 2020

Previous ID SR-12459
Radar rdar://problem/62202443
Original Reporter @ahoppen
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, TypeChecker
Assignee @ahoppen
Priority Medium

md5: 886bc3d5b61b666595f45872e20f5f63

Issue Description:

Take a look at the following code:

protocol Foo {}


extension Foo {
  static func ==(lhs: Foo, rhs: Foo) -> Bool {
    fatalError()
  }
}


struct Bar: Foo {}

let a: Foo = Bar()
let b: Foo = Bar()
print(a == b) // Error: Binary operator '==' cannot be applied to two 'Foo' operands

I would expect a == b to call the == operator declared in the extension of Foo. However, I get an error „Binary operator '==' cannot be applied to two 'Foo' operands“.

Using Swift 5.2 shipped with Xcode 11.4 (11E146, swiftlang-1103.0.32.1)
@hamishknight
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The problem is that there's no way to infer the type for the implicit Self parameter, we should probably emit a warning explaining this to the user and suggest making it a top-level operator function instead.

@ahoppen
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ahoppen commented Apr 3, 2020

A warning sounds like a good solution to me if it's not easy to get it to work 👍

@beccadax
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@swift-ci create

@theblixguy
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On master, the diagnostic now says:

/Users/spare/Desktop/test.swift:15:9: error: generic parameter 'Self' could not be inferred
print(a == b)
        ^

@xedin
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xedin commented Mar 30, 2021

I think diagnostic about `generic parameter 'Self' could not be inferred` makes sense here.

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

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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis
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@xedin @beccadax @theblixguy @ahoppen @hamishknight