Why can I mutate a let constant with inout parameter when using try?

Asked Jul 25 '18 at 20:10

Active Jul 25 '18 at 20:33

Viewed 94 times

This will fail to compile with the error:

Immutable value 'self.constantValue' must not be passed inout

class Test {
    let constantValue: String = ""


    init() {
        Test.makeABC(&constantValue)
    }

    static func makeABC(_ string: inout String) {
        string = "ABC"
    }
}

However this will compile and actually mutate the let constant.

class Test {
    let constantValue: String = ""


    init() {
        try? Test.makeABC(&constantValue)
    }

    static func makeABC(_ string: inout String) throws {
        string = "ABC"
    }
}

Does anyone know why this works and if it is intended behavior?

I have filed a bug https://bugs.swift.org/browse/SR-8368

edited Jul 25 '18 at 20:33

asked Jul 25 '18 at 20:10

wshamp

1

That looks like a bug to me. – Martin R Jul 25 '18 at 20:22
2

@MartinR Interestingly, this behavior is confined to `init`. Move the `try?` to a normal method and the compiler rejects that one too. – matt Jul 25 '18 at 20:25
Fixed typo AnotherTest to just Test – wshamp Jul 25 '18 at 20:34
1

Congratulations on finding a great edge case! We always like it when that happens. Well done. – matt Jul 25 '18 at 21:41

Why can I mutate a let constant with inout parameter when using try?

0 Answers0