Swift 3.0 iterate over String.Index range

Question

The following was possible with Swift 2.2:

let m = \"alpha\"
for i in m.startIndex..

With 3.0,

Answer 1

To concretely demonstrate how to traverse through a range in a string in Swift 4, we can use the where filter in a for loop to filter its execution to the specified range:

func iterateStringByRange(_ sentence: String, from: Int, to: Int) {

    let startIndex = sentence.index(sentence.startIndex, offsetBy: from)
    let endIndex = sentence.index(sentence.startIndex, offsetBy: to)

    for position in sentence.indices where (position >= startIndex && position < endIndex) {
        let char = sentence[position]
        print(char)
    }

}

iterateStringByRange("string", from: 1, to: 3) will print t, r and i