regex.swift

import Foundation

/// Provides NSRegularExpression pattern matching
/// against strings in `switch` and `~=` statements
public struct Regex {
    public let regexPattern: String
    public let options: NSRegularExpression.Options
    
    /// Initialize a `Regex` instance that
    /// defaults to no options. Update as needed for
    /// case or diacritical insensitivity
    ///
    /// - parameter regexPattern: The matching pattern
    /// - parameter options: any `NSRegularExpression.Options`, defaulting to []
    public init(_ regexPattern: String, _ options: NSRegularExpression.Options = []) {
        (self.regexPattern, self.options) = (regexPattern, options)
    }
    
    /// Extends pattern matching to use the pattern and
    /// options stored in the `Regex` matcher
    public static func ~=  (lhs: Regex, rhs: String) -> Bool {
        guard let regex = try? NSRegularExpression(pattern: lhs.regexPattern, options: lhs.options)
            else { return false }
        let range = NSRange(location: 0, length: rhs.utf16.count)
        if let _ = regex.firstMatch(in: rhs, range: range) { return true }
        return false
    }
}

// For example

let str = "Hello, playground"

str ~= "Hello" // false
str ~= "Hello, playground" // true
Regex("H.*o") ~= str // true
Regex("H.*o") ~= "Out of luck" // false

// matches
switch str {
case Regex("H.*o"): print("Hello to you!")
default: print("Nope")
}

// does not match
switch "Out of luck" {
case Regex("H.*o"): print("Hello to you!")
default: print("Nope")
}