ExpressibleByIntegerLiteral

Question

makabaka1880 OP

Created Aug ’22

Replies 1

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Participants 2

I tried to implement ExpressibleByIntegerLiteral to my code and it has been terrible.

At last, it asked me to implement this init

// Cannot find type 'Builtin' in scope
init(_builtinIntegerLiteral value: Builtin.IntLiteral) { 
}

Answered by DTS Engineer in 723171022

The ExpressibleByIntegerLiteral protocol has an associated type, IntegerLiteralType, that you must define to be one of the standard integer literal types. You can do this explicitly but most folks do it implicitly, by supplying that type in their init(integerLiteral:) definition. For example:

struct CDTrack {
    var value: Int16
}

extension CDTrack: ExpressibleByIntegerLiteral {
    init(integerLiteral value: Int16) {
        self.value = value
    }
}

let trackA: CDTrack = 32767

Here the parameter to init(integerLiteral:) is Int16, and that becomes the IntegerLiteralType associated type. Now the compiler is able to check that the integer literal is in bounds. For example, this code fails to compile:

let trackB: CDTrack = 32768
                      ^ Integer literal '32768' overflows when stored into 'CDTrack'

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let myEmail = "eskimo" + "1" + "@" + "apple.com"

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Answer 1

DTS Engineer OP

Apple

Aug ’22

Accepted Answer

The ExpressibleByIntegerLiteral protocol has an associated type, IntegerLiteralType, that you must define to be one of the standard integer literal types. You can do this explicitly but most folks do it implicitly, by supplying that type in their init(integerLiteral:) definition. For example:

struct CDTrack {
    var value: Int16
}

extension CDTrack: ExpressibleByIntegerLiteral {
    init(integerLiteral value: Int16) {
        self.value = value
    }
}

let trackA: CDTrack = 32767

Here the parameter to init(integerLiteral:) is Int16, and that becomes the IntegerLiteralType associated type. Now the compiler is able to check that the integer literal is in bounds. For example, this code fails to compile:

let trackB: CDTrack = 32768
                      ^ Integer literal '32768' overflows when stored into 'CDTrack'

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

0