Automatic Type Conversion with extension: What is happening here?

swift

Solution

Yes, the extension you wrote is actually only for `Double`s, not for `Int`s. Take a look at this example:

extension Double {
    var absoluteValue: Double {
        if (self < 0) {
            return self * -1
        }

        return self
    }
}

var double: Int = 10
double.absoluteValue // Int does not have a member named absoluteValue

But, in your code the compiler is implicitly converting your `Int` to a `Double`.

Problem

I'm going through the first chapter of `The Swift Programming Language` book and I'm at the part where it's describing the `extension` keyword. I had a go at the "Experiment": “Write an extension for the Double type that adds an absoluteValue property.” I got it working like this: ``` extension Double { var absoluteValue: Double { if(self < 0) { return self * -1 } return self } } (-10.5).absoluteValue // 10.5 ``` But it also seems to work for integers: ``` (-4).absoluteValue // 4.0 ``` What is happening here? Is the compiler changing the type from `Int` to `Double` because it sees that there is a `absoluteValue` extension on `Double` but not `Int`? This appears to be the case because if I add another `extension` of the same name on `Int` like so: ``` extension Int { var absoluteValue: Int { return 42 } } ``` That overrides the `extension` on `Double`. And `(-4).absoluteValue` returns `42` Is there a way to add an `extension` that only works on `Double`s but not `Int`s? Edit: Looks like it's doing a conversion at compile-time and since I didn't define a type for my literal it converted it. The following produces an error ``` var i:Int = -4; i.absoluteValue ``` "Playground execution failed: error: :12:1: error: 'Int' does not have a member named 'absoluteValue' i.absoluteValue ^ ~~~~~~~~~~~~~" Edit 2: It appears to only apply to literals; the following also produces an error: ``` var i = -4; i.absoluteValue ```

Original source