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[SR-3702] Generic matching ignores function-type alternative in favor of non-function-type alternative #46287

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swift-ci opened this issue Jan 24, 2017 · 3 comments
Open

[SR-3702] Generic matching ignores function-type alternative in favor of non-function-type alternative #46287

swift-ci opened this issue Jan 24, 2017 · 3 comments
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@DougGregor
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 3.0 type checker Area → compiler: Semantic analysis

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@swift-ci
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Previous ID SR-3702
Radar None
Original Reporter bromine (JIRA User)
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 3.0Regression, TypeChecker
Assignee @DougGregor
Priority Medium

md5: 6f7aea53970e5598c3e985ce953a1950

Issue Description:

Given declaration of (T) -> String and (() -> T) -> String, Swift 2 would choose the latter whereas Swift 3 chooses the former when a function argument is passed. Questions: is this intentional? Is this desirable? Is there a way to get Swift 2 behavior in Swift 3?

Example code:

func test<T>(_ x: T) -> String {
    return "From not-a-maker \(x)"
}

func test<T>(_ x: () -> T) -> String {
    return "From other maker \(x), producing \(x())"
}

func test(_ x: () -> String) -> String {
    return "From string maker \(x), producing \(x())"
}

func test(_ x: () -> Int) -> String {
    return "From int maker \(x), producing \(x())"
}

print("T str closure: \(test({"a"}))")
print("T int closure: \(test({1}))")
print("T float closure: \(test({1.0}))")

Swift 2 output:

T str closure: From string maker (Function), producing a
T int closure: From int maker (Function), producing 1
T float closure: From other maker (Function), producing 1.0

Swift 3 output:

T str closure: From not-a-maker (Function)
T int closure: From not-a-maker (Function)
T float closure: From not-a-maker (Function)
@belkadan
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I have no idea what we changed here. @DougGregor?

@DougGregor
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That's really odd. I don't know why this changed---the latter function should be considered "more specialized".

@swift-ci
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Comment by Ben Artin (JIRA)

Yeah, that's what I suspected. Thanks for confirming.

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

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 3.0 type checker Area → compiler: Semantic analysis
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@belkadan @DougGregor @swift-ci @AnthonyLatsis