Split a String without removing the delimiter in Swift

Question

This might be a duplicate. I couldn\'t find the answer in Swift, so I am not sure.

componentsSeparatedByCharactersInSet removes the delimiter. If you se

Answer 1

I came here looking for an answer to this question. Didn't find what I was looking for and ended up building this by repeated calls to .split(...) It isn't elegant but you can choose which delimiters are preserved and which aren't. There's probably a way to avoid the String <--> Substring conversions, anyone know?

var input = """
    {All those moments will be (lost in time)},
    like tears [in rain](. ([(Time to)] die))
"""
var separator: Character = "!"
var output: [String] = []
repeat {
    let tokens = input.split(
        maxSplits: 1,
        omittingEmptySubsequences: false,
        whereSeparator: {
            switch $0 {
                case "{", "}", "(", ")", "[", "]": // preserve
                    separator = $0; return true
                case " ", "\n", ",", ".":          // omit
                    separator = " "; return true
                default:
                    return false
            }
        }
    )
    if tokens[0] != ""  { 
        output.append(String(tokens[0])) 
    }
    guard tokens.count == 2 else { break }
    if separator != " " { 
        output.append(String(separator)) 
    }
    input = String(tokens[1])
} while true

for token in output { print("\(token)") }

In the case above, the selectors are not in actual sets. I didn't need that, but if you do, simply make these declarations,

let preservedDelimiters: Set = [ "{", "}", "(", ")", "[", "]" ]
let omittedDelimiters: Set = [ " ", "\n", ",", "." ]

and replace the whereSeparator function with:

whereSeparator: {
    if preservedDelimiters.contains($0) {
        separator = $0
        return true
    } else if omittedDelimiters.contains($0) {
        separator = " "
        return true
    } else {
        return false
    }
}