Regex warning.

PatternMatch.swift

import Foundation

// from https://www.hackingwithswift.com/articles/108/how-to-use-regular-expressions-in-swift

extension String {
    static func ~= (lhs: String, rhs: String) -> Bool {
        guard let regex = try? NSRegularExpression(pattern: rhs) else { return false }
        let range = NSRange(location: 0, length: lhs.utf16.count)
        return regex.firstMatch(in: lhs, options: [], range: range) != nil
    }
}

// Notice how applying the extension overrides the natural behaviour of `case`.
// Run this in a playground, then comment out the extension and compare the results.

switch "hello" {
case "hello world":
    print("'Hello' matches 'Hello world'!")
default:
    print("'Hello' doesn't match 'Hello world'. All is well.")
}