String access (set AND get) by int indices or ranges in Swift 5.

String-int-extension.swift

/**
 * 
 * Since Swift has no concept of real world String uses, I just had to make this extension.
 * With this extension you can set and get following:
 *
 * Access String by Int index:
 * let second = string[1]
 * 
 * Set value by index or range:
 * string[1] = "a"
 * string[1] = "asdf" // Yep, even this works
 * string[1...2]
 * string[1..<2]
 * string[1...]
 * string[...2]
 * string[..<2]
 * 
 */
extension String {
    
    // Covers string[index]
    subscript (_ idx: Int) -> String {
        get {
            return String(self[index(startIndex, offsetBy: idx)])
        }
        set (newValue) {
            replaceSubrange(index(startIndex, offsetBy: idx)..<index(startIndex, offsetBy: idx + 1), with: newValue)
        }
    }
    
    // Covers string[start..<end]
    subscript (_ range: Range<Int>) -> String {
        get {
            let start = index(startIndex, offsetBy: range.lowerBound)
            let end = index(startIndex, offsetBy: range.upperBound)
            return String(self[start...end])
        }
        set (newValue) {
            let start = index(startIndex, offsetBy: range.lowerBound)
            let end = index(startIndex, offsetBy: range.upperBound)
            if (range.lowerBound >= count) {
                self += newValue
            } else {
                replaceSubrange(start...end, with: newValue)
            }
        }
    }
    
    // Covers string[start...end]
    subscript (_ range: ClosedRange<Int>) -> String {
        get {
            let start = index(startIndex, offsetBy: range.lowerBound)
            let end = index(startIndex, offsetBy: range.upperBound)
            return String(self[start...end])
        }
        set (newValue) {
            let start = index(startIndex, offsetBy: range.lowerBound)
            let end = index(startIndex, offsetBy: range.upperBound)
            if (range.lowerBound >= count) {
                self += newValue
            } else {
                replaceSubrange(start...end, with: newValue)
            }
        }
    }
    
    // Covers string[start...]
    subscript (_ range: PartialRangeFrom<Int>) -> String {
        get {
            let start = index(startIndex, offsetBy: range.lowerBound)
            let end = index(startIndex, offsetBy: count-1)
            return String(self[start...end])
        }
        set (newValue) {
            let start = index(startIndex, offsetBy: range.lowerBound)
            let end = index(startIndex, offsetBy: count-1)
            if (range.lowerBound >= count) {
                self += newValue
            } else {
                replaceSubrange(start...end, with: newValue)
            }
        }
    }

    // Covers string[...end]
    subscript (_ range: PartialRangeThrough<Int>) -> String {
        get {
            let start = index(startIndex, offsetBy: 0)
            let end = index(startIndex, offsetBy: range.upperBound)
            return String(self[start...end])
        }
        set (newValue) {
            let start = index(startIndex, offsetBy: 0)
            let end = index(startIndex, offsetBy: range.upperBound)
            replaceSubrange(start...end, with: newValue)
        }
    }

    // Covers string[..<end]
    subscript (_ range: PartialRangeUpTo<Int>) -> String {
        get {
            let start = index(startIndex, offsetBy: 0)
            let end = index(startIndex, offsetBy: range.upperBound)
            return String(self[start...end])
        }
        set (newValue) {
            let start = index(startIndex, offsetBy: 0)
            let end = index(startIndex, offsetBy: range.upperBound)
            replaceSubrange(start...end, with: newValue)
        }
    }
}

var string = "I'm a string";
assert(string == "I'm a string")
string[1] = " a"
assert(string == "I am a string")
string[1...3] = "'m not"
assert(string == "I'm not a string")
string[9..<9] = " particular "
assert(string == "I'm not a particular string")
string[...2] = "I am"
assert(string == "I am not a particular string")
string[28...] = "! Or am I?"
assert(string == "I am not a particular string! Or am I?")
string[..<3] = "I'm"
assert(string == "I'm not a particular string! Or am I?")