如何创建允许加载对象的界面？

Question

I have created an interface meant to be implemented by users. The only real requirements I have is that the user's implement a Save() and a Load() method. Now save is simple, but the problem I'm having is with Load().

In order for Load() to be part of the interface it would need to be an instance method. But the nature of it is to return a new object that has been loaded from a database. This would imply that Load() needs to be defined as static. Static methods aren't enforced by the interface.

How can I require users who implement the interface to write their own code for Load()?

I'm using PHP5.4 which does require that constructor definitions are followed in subclasses, so one thought was to change this into an Abstract Class and define a constructor that takes an $id variable. If it's null we create a new object, if it's set then load the object. I'd much prefer to keep this setup as an interface. There also is some concern of ambiguity and some user implementing their constructor incorrectly. It's easier to document and describe what load() should do.

Answer 1

Why does "a method that returns an object" immediately mean that it has to be static? Static isn't a blanket "go-to" on object creation - it actually serves a specific purpose.

Anyway. There is nothing stopping you from defining an interface that requires the implementation of a static method, as follows, if your heart so desires :

interface MyTestInterface {
   public static function Load();
}
class MyTest implements MyTestInterface {
   public static function Load() { 
       echo "Test";
   }
}

Fiddle: http://codepad.viper-7.com/xcoQZh

There is nothing stopping you from defining a method requiring implementation, either through an interface or an abstract class, when the method is static. However, consider the actual static use in this case....