Swift find all occurrences of a substring

Question

I have an extension here of the String class in Swift that returns the index of the first letter of a given substring.

Can anybody please help me make it so it will

Answer 1

Here are 2 functions. One returns [Range], the other returns [Range]. If you don't need the former, you can make it private. I've designed it to mimic the range(of:options:range:locale:) method, so it supports all the same features.

import Foundation

extension String {
    public func allRanges(
        of aString: String,
        options: String.CompareOptions = [],
        range: Range? = nil,
        locale: Locale? = nil
    ) -> [Range] {

        // the slice within which to search
        let slice = (range == nil) ? self[...] : self[range!]

        var previousEnd = s.startIndex
        var ranges = [Range]()

        while let r = slice.range(
            of: aString, options: options,
            range: previousEnd ..< s.endIndex,
            locale: locale
        ) {
            if previousEnd != self.endIndex { // don't increment past the end
                    previousEnd = self.index(after: r.lowerBound)
            }
            ranges.append(r)
        }

        return ranges
    }

    public func allRanges(
        of aString: String,
        options: String.CompareOptions = [],
        range: Range? = nil,
        locale: Locale? = nil
    ) -> [Range] {
        return allRanges(of: aString, options: options, range: range, locale: locale)
            .map(indexRangeToIntRange)
    }


    private func indexRangeToIntRange(_ range: Range) -> Range {
        return indexToInt(range.lowerBound) ..< indexToInt(range.upperBound)
    }

    private func indexToInt(_ index: String.Index) -> Int {
        return self.distance(from: self.startIndex, to: index)
    }
}

let s = "abc abc  abc   abc    abc"
print(s.allRanges(of: "abc") as [Range])
print()
print(s.allRanges(of: "abc") as [Range])