Swift Reverse String In Place Using Indices

func reverse(_ str: inout String) {
    if str.isEmpty {
        return
    }
    var leftPointer = str.startIndex
    var rightPointer = str.index(before: str.endIndex)
    while leftPointer < rightPointer {
        let leftChar = str[leftPointer]
        str.replaceSubrange(leftPointer..<str.index(after: leftPointer), with: String(str[rightPointer]))
        str.replaceSubrange(rightPointer..<str.index(after: rightPointer), with: String(leftChar))
        if leftPointer < str.endIndex {
            leftPointer = str.index(after: leftPointer)
        }
        if rightPointer > str.startIndex {
            rightPointer = str.index(before: rightPointer)
        }
    }
}

// NICE WORK!

// I made it a String extension with a mutating func

extension String {
    mutating func reverseInline() {
        if self.isEmpty {
            return
        }
        var leftPointer = self.startIndex
        var rightPointer = self.index(before: self.endIndex)
        while leftPointer < rightPointer {
            let leftChar = self[leftPointer]
            self.replaceSubrange(leftPointer..<self.index(after: leftPointer), with: String(self[rightPointer]))
            self.replaceSubrange(rightPointer..<self.index(after: rightPointer), with: String(leftChar))
            if leftPointer < self.endIndex {
                leftPointer = self.index(after: leftPointer)
            }
            if rightPointer > self.startIndex {
                rightPointer = self.index(before: rightPointer)
            }
        }
    }
}