Swift-实例“无法用'...”构造为“静态”方法

Question

When I try to instantiate a class through "static" method (required from protocol), the compiler don't recognize the initializer, although I pass correct parameters.

Answer 1

The problem is that you are defining a template called "Comment" in your method declaration that is obscuring the real Comment class. You need to give that template argument a different name.

And I believe your JSONSerializable protocol is not defined the way you want it. You can use Self in a protocol to refer to the class implementing the protocol so there is no need for a template. Your protocol could look like this:

protocol JSONSerializable {
    class func instanceFrom(json: [String:AnyObject]) -> Self;
}

Then you would implement this method in your Comment class:

class Comment: JSONSerializable {
    ...

    class func instanceFrom(json: [String:AnyObject]) -> Comment {
        return Comment(message: "lorem lorem", author: User())
    }
}

However, it is preferred in Swift to use initializers instead of class methods:

protocol JSONSerializable {
    init(json: [String:AnyObject])
}

class Comment: JSONSerializable {
    ...

    init(json: [String : AnyObject]) {
    }
}