Swift协议定义返回self的类方法-Swiftprotocoldefiningclassmethodreturningself

2  

Self in a protocol is a requirement that implementations of the protocol use their own type. Since Invoice is the type you're adopting the protocol in, your implementation of FromJson should have a return type of Invoice.

协议中的Self要求协议的实现使用它们自己的类型。由于Invoice是您采用协议的类型,因此FromJson的实现应具有Invoice的返回类型。

4  

It's right. Your method is declared to return Self, whereas you are returning Invoice. Class methods are inherited, and in subclasses, Self will be that subclass type, and Invoice is not a subtype of that type.

这是正确的。声明您的方法返回Self,而您返回Invoice。类方法是继承的,在子类中,Self将是该子类类型,而Invoice不是该类型的子类型。

To actually return Self, assuming Invoice has a required init() constructor, you can do something like this:

要实际返回Self,假设Invoice具有必需的init()构造函数,您可以执行以下操作:

extension Invoice : CanDeserialiseFromJson {
    class func FromJson(json : JSONValue) -> Self {
        return self()
    }
}