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[SR-14731] Self<T> is allowed in generic type, but it doesn't work as expected. #57081

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swift-ci opened this issue Jun 6, 2021 · 4 comments
Closed

[SR-14731] Self<T> is allowed in generic type, but it doesn't work as expected. #57081

swift-ci opened this issue Jun 6, 2021 · 4 comments
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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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@swift-ci
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swift-ci commented Jun 6, 2021

Previous ID SR-14731
Radar rdar://problem/79051797
Original Reporter ensan (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

Apple Swift version 5.4 (swiftlang-1205.0.26.9 clang-1205.0.19.55)
Target: x86_64-apple-darwin20.5.0

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

md5: a6580430cf4875efea2b6580bfa43a4f

Issue Description:

I couldn't find previous report about this behavior. Perhaps this is a known-issue, but just in case.

struct Wrapper<A> {
    // actually WrapperInt is Wrapper<A>
    typealias WrapperInt = Self<Int>
}

I read https://bugs.swift.org/browse/SR-7666, but about this, compiler should cause at least warning, because it must not work as expected. If `Self` stands for `Wrapper`, it should work as expected. If `Self` stands for `Wrapper<A>` then it should be error, because `Wrapper<A><Int>` doesn't make sense.
@typesanitizer
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You're right, this should be an error instead of being silently ignored.

@swift-ci create

@CodaFi
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CodaFi commented Jun 10, 2021

Huh, seems like we're not substituting this thing correctly

struct Wrapper<A> {
    // actually WrapperInt is Wrapper<A>
    typealias WrapperInt = Self<Int>

    func eat(_ x: WrapperInt) {
      x.foo() // error!
    }
}

extension Wrapper where A == Int {
  func foo() {}
}

@slavapestov
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Yeah, I agree that this should be an error. The original proposal did not say anything about substituting in alternate generic arguments with `Self`.

@slavapestov
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#37891

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