replacing.swift

import Foundation

public extension String {
    public func replacing(range: CountableClosedRange<Int>, with replacementString: String) -> String {
        let start = characters.index(characters.startIndex, offsetBy: range.lowerBound)
        let end   = characters.index(start, offsetBy: range.count)
        return self.replacingCharacters(in: start ..< end, with: replacementString)
    }
}

var test = "Forty Two"
for index in 1...test.characters.count {
    print(test.replacing(range: 1 ... index, with: "XXXX"))
}

// See also:

infix operator ..+ {}
public func ..+ <Bound: Strideable>(lhs: Bound, rhs: Bound.Stride) -> CountableClosedRange<Bound> {
    return lhs ... lhs.advanced(by: rhs)
}

test.replacing(range: 1 ..+ 2, with: "XXXX")