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Swift 3 Extend Range of Specific Type

Having trouble grasping what the syntax would be for extending a Range of a specific type/types. For example, if I only wanted to extend Range<Double> or Range<Int> or both.

Solution

  • You can't directly. It's a currently missing feature of Swift. You can get around it by using a dummy protocol:

    protocol _Int {}
extension Int: _Int {}

extension CountableClosedRange where Bound: _Int {
    var sum: Int {
        // These forced casts are acceptable because
        // we know `Int` is the only type to conform to`_Int`
        let lowerBound = self.lowerBound as! Int
        let upperBound = self.upperBound as! Int
        let count = self.count as! Int

        return (lowerBound * count + upperBound * count) / 2
    }
}

print((1...100).sum) //5050

    The FloatingPoint or Integer protocols may also be useful here.