像往常一样，用字符串当key 缺点：

• 容易拼写错误
• 重复定义
• 多人开发项目,难于管理

eg:

import Foundationimport UIKitprotocol UserDefaultNameSpace {}extension UserDefaultNameSpace {    static func namespace
    
     (_ key:T) -> String where T: RawRepresentable {        return "\(Self.self).\(key.rawValue)"    }}protocol UserDefaultSettable: UserDefaultNameSpace {    associatedtype UserDafaultKey: RawRepresentable}extension UserDefaultSettable where UserDafaultKey.RawValue == String {}extension UserDefaultSettable {    /// 关于 Int 类型的存储和读取    static func set(value: Int, forKey key: UserDafaultKey) {        let key = namespace(key)        UserDefaults.standard.set(value, forKey: key)            }        static func integer(value: Int, forKey key: UserDafaultKey) {        let key = namespace(key)        UserDefaults.standard.integer(forKey: key)    }        /// 关于 String 类型存储和读取    static func set(value: Any?, forKey key: UserDafaultKey) {        let key = namespace(key)        UserDefaults.standard.set(value, forKey: key)    }        static func string(value: Any?, forKey key: UserDafaultKey) {        let key = namespace(key)        UserDefaults.standard.string(forKey: key)    }}// MARK: - 使用方式extension UserDefaults {    struct Account: UserDefaultSettable {        enum  UserDafaultKey: String {            case name            case age            case birth        }    }}class test {    func testFunction() {        UserDefaults.Account.set(value: 20, forKey: .age)        UserDefaults.Account.set(value: "hjq", forKey: .name)    }}复制代码