ios – Swift：协议默认实现 – didSet

我怎样才能将默认实现didSet设置为protocol var
我试试,但我有错误

Extensions may not contain stored properties

protocol MyProtocol {
    var contact: MyContact? { get set }
}

extension MyProtocol {
    var contact: MyContact? {
        didSet {
            // some code
        }
    }
}

解决方法

来自文档：

Extensions can add new computed properties,but they cannot add stored properties,or add property observers to existing properties.

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Extensions.html#//apple_ref/doc/uid/TP40014097-CH24-ID151

如果要设置联系人的默认值,则必须是计算属性.

extension MyProtocol {
  var contact: MyContact? {
    return MyContact()
  }
}