Bool関連のStringをBoolに変換するExtension

#Purpose
Personal Note
あんまり使いませんが使用する機会があったのでとりあえずメモ

#Development Environment

• OS X El Captain 10.11.2
• Xcode Version 8.0

#Language
Swift 3.0

#Code

extension String {    
   func toBool() -> Bool? {
       switch self {
       case "TRUE", "True", "true", "YES", "Yes", "yes", "1":
           return true
       case "FALSE", "False", "false", "NO", "No", "no", "0":
           return false
       default:
           return nil
       }
   }
}