[SR-5181] Protocol extension with constrained associated type doesn't work when using custom operator #47757

swift-ci · 2017-06-10T00:15:08Z


Previous ID	SR-5181
Radar	rdar://problem/33142387
Original Reporter	inamiy (JIRA User)
Type	Bug

Environment

Xcode Version 9.0 beta (9M136h)

Additional Detail from JIRA


Votes	0
Component/s	Compiler
Labels	Bug, TypeChecker
Assignee	@xedin
Priority	Medium

md5: 0a78b8ece4c44ce927fa4a680a607c65

is duplicated by:

SR-7476 Incorrect “ambiguous operator” error

Issue Description:

protocol Addable {
    associatedtype SomeType
    
    static func + (a: Self, b: Self) -> Self
    func sayHello()
    static func sayHello()
}

extension Addable {
    static func + (a: Self, b: Self) -> Self {
        print("add<default>")
        return a
    }
    
    func sayHello() {
        print("hello<default>")
    }
    
    static func sayHello() {
        print("hello<default>")
    }
}

extension Addable where SomeType == Int {
    static func + (a: Self, b: Self) -> Self {
        print("add<Int>")
        return a
    }
    
    func sayHello() {
        print("hello<Int>")
    }
    
    static func sayHello() {
        print("hello<Int>")
    }
}

struct Concrete<T>: Addable {
    typealias SomeType = T
}

let a = Concrete<Int>()

a.sayHello()             // OK: prints hello<Int>
Concrete<Int>.sayHello() // OK: prints hello<Int>

a + a                    // Not OK: prints add<default> ... why?

And when static func + (a: Self, b: Self) -> Self is commented out, a + a will work correctly.

See also: https://gist.github.com/taketo1024/88af341a8bf51af2bc133dee08cff3ae

The text was updated successfully, but these errors were encountered:

belkadan · 2017-06-10T01:19:35Z

Seems like a bug that they're inconsistent, but note that you're probably not getting the behavior you think you are:

func callSayHello<T: Addable>(_ obj: T) {
  obj.sayHello()
}
callSayHello(a) // default

What's happening is that Concrete has to pick one implementation of each requirement no matter what generic parameter it gets instantiated with. You'd have to call some method on the generic parameter or check the type with as? to get different behavior in a generic context.

I'm not sure why + is being treated different than sayHello in the fully-concrete context, though.

belkadan · 2017-06-10T01:19:46Z

cc @rudkx, @xedin

rudkx · 2017-07-05T22:03:20Z

@swift-ci create

xedin · 2018-04-11T21:47:38Z

Currently the behavior is that we consider something found in the declaration of the nominal better than anything which is declared in extension, that's why removing declaration from the protocol make everything behave as expected. I think we need to refine how we do look up and use only default implementation instead of both which would lead to a correct behavior in this case.

xedin · 2018-07-19T01:09:27Z

inamiy (JIRA User) Sorry for the delay, I had couple of PRs out to try and correct this inconsistency but unfortunately there is no easy fix for it and it requires swift evolution discussion, which might be a part of apple/swift-evolution#857

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

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[SR-5181] Protocol extension with constrained associated type doesn't work when using custom operator #47757

[SR-5181] Protocol extension with constrained associated type doesn't work when using custom operator #47757

swift-ci commented Jun 10, 2017

belkadan commented Jun 10, 2017

belkadan commented Jun 10, 2017

rudkx commented Jul 5, 2017

xedin commented Apr 11, 2018

xedin commented Jul 19, 2018

[SR-5181] Protocol extension with constrained associated type doesn't work when using custom operator #47757

[SR-5181] Protocol extension with constrained associated type doesn't work when using custom operator #47757

Comments

swift-ci commented Jun 10, 2017

belkadan commented Jun 10, 2017

belkadan commented Jun 10, 2017

rudkx commented Jul 5, 2017

xedin commented Apr 11, 2018

xedin commented Jul 19, 2018