get all ranges of a substring in a string in swift

Question

I have a string for example \"ab ad adk fda kla kad ab ab kd\". I want to get all range of ab.(Here ab is present at 3 position so I should get 3 range).In normal scenarion

Answer 1

Swift 5:

The improved version of the most popular answer:

extension String {    
    func ranges(of substring: String, options: CompareOptions = [], locale: Locale? = nil) -> [Range] {
        var ranges: [Range] = []
        while let range = range(of: substring, options: options, range: (ranges.last?.upperBound ?? self.startIndex)..