rex.swift

import Foundation

// Extend String to support regex searching by conforming
// to CustomStringConvertible
extension String: CustomStringConvertible {
    public var description: String {return self}
}

// Regex support for keys
public extension Dictionary where Key: CustomStringConvertible {
    
    /// Return keys that match the supplied Key expressed as string
    public subscript (regexKeys regex: Key) -> [Key] {
        get {
            
            // I went with a pretty flexible case insensitive
            // search here. Tweak as desired.
            let options: NSStringCompareOptions = [
                .RegularExpressionSearch,
                .CaseInsensitiveSearch,
                .DiacriticInsensitiveSearch
            ]
            
            let stringRex = String(regex)
            return keys.filter({
                // Thanks Patrick Smith, http://twitter.com/concreteniche/status/701906479645794304
                return ($0.description as NSString)
                    .rangeOfString(stringRex, options: options)
                    .location != NSNotFound
            })
        }
    }
    
    /// Return values that match the regex Key
    public subscript (regex regex: Key) -> [Value] {
        return self[regexKeys: regex].flatMap({ self[$0] })
    }
}

let sample = [
    "monday": "mValue",
    "tuesday": "tValue",
    "weds": "wValue",
    "thursday": "thValue"]
print(sample[regex: ".*day"])
print(sample[regexKeys: ".*day"])