enumCast()

enumCast.swift

import Foundation

func enumCast<C1, C2: RawRepresentable where C2.RawValue == C1>(rawValue: C1?) -> C2? {
    if let rawValue = rawValue {
        return C2(rawValue: rawValue)
    } else {
        return nil
    }
}

func enumCast<C1, C2: RawRepresentable where C2.RawValue == C1>(rawValue: C1) -> C2? {
    return C2(rawValue: rawValue)
}

// example

enum HogeFuga: String {
    case Hoge = "hoge"
    case Fuga = "fuga"
}

var s: String?
s = "hoge"

// using enumCast()
if let hogefuga: HogeFuga = enumCast(s) {
    println(hogefuga)
} else {
    println("err")
}

// without enumCast()
if let s = s {
    if let hogefuga = HogeFuga(rawValue: s) {
        println(hogefuga)
    } else {
        println("err")
    }
} else {
    println("err")
}