Life-saving String extension for Swift >= 5.0 easing the split–filter–join flows.

Swift5_String+Ex.swift

import Foundation

#if swift(>=5.0)

extension StringProtocol where Index == String.Index {

    func split(string str: String) -> [Substring] {

        var si = self.startIndex
        let ei = self.endIndex

        var ret = [Substring]()

        if str == "" {
            while si != ei {
                let next = self.index(after: si)
                if let ss = self[si..<next] as? Substring
                {
                    if (self.distance(from: self.startIndex, to: next) > 0) {
                        ret.append(ss)
                    }
                }
                si = next
            }
        }

        repeat
        {
            if let r = self.range(of: str, options: [], range: (si..<ei), locale: nil) {
                if let ss = self[si..<r.lowerBound] as? Substring
                {
                    if (self.distance(from: self.startIndex, to: r.lowerBound) > 0) {
                        ret.append(ss)
                    }
                }
                si = r.upperBound
                if si >= ei { break }
//              if si > ei { break } // switch to include empty element at the end
            }
            else {
                if let ss = self[si..<ei] as? Substring
                {
                    ret.append(ss)
                }
                break
            }
        } while true

        return ret.filter { !$0.isEmpty }
    }
}

extension Array where Element : StringProtocol {
    func join(string str: String) -> String {
        return self.joined(separator: str)
    }
}

// Sample use

"máslo, sádlo, banány, lovec, kámen"
    .split(string: ", ")
    .filter { $0.contains("lo") }
    .join(string: " ☢️ ")

// Tests & Ruby result equality

"".split(string: " ")
// ✅ []

"a".split(string: " ")
// ✅ ["a"]

"a b c d".split(string: " ")
// ✅ ["a","b","c","d"]

" a b c d".split(string: " ")
// ✅ ["a","b","c","d"]

"  a b c d".split(string: " ")
// ✅ ["a","b","c","d"]

"a b c d ".split(string: " ")
// ✅ ["a","b","c","d"]

"a b c d  ".split(string: " ")
// ✅ ["a","b","c","d"]

"   a     b c   d  ".split(string: " ")
// ✅ ["a","b","c","d"]

"a b c d  ".split(string: " o")
// ✅ ["a b c d  "]

"abcd".split(string: "")
// ✅ ["a","b","c","d"]

"          ".split(string: "")
// ✅ [" "," "," "," "," "," "," "," "," "," "]

"👀😁🙈😄".split(string: "")
// ✅ ["👀","😁","🙈","😄"]

#endif