PHP Late Static Binding in Singleton?

All of the classes share the same static array, $_instances, contained in the Singleton class. The reason the author used "new static;" was to store an object of the called class in that array. Because there is only one array, self:: and static:: calls on that array from within the Singleton class will return the same data So, to clarify, when you call: $b_instance = B::getInstance() an instance of B is being added to the $_instances array stored within Singleton.

If you added a static $_instances property to the B or C class, the behaviour would be different, in that the newly created instance would be stored inside its own classes static $_instances property.

All of the classes share the same static array, $_instances, contained in the Singleton class. The reason the author used "new static;" was to store an object of the called class in that array. Because there is only one array, self:: and static:: calls on that array from within the Singleton class will return the same data.So, to clarify, when you call: $b_instance = B::getInstance(); an instance of B is being added to the $_instances array stored within Singleton.

If you added a static $_instances property to the B or C class, the behaviour would be different, in that the newly created instance would be stored inside its own classes static $_instances property.

Thank you very much. But, as last question: if I write "static::$_instances", PHP interprete it as "instances array of B", when B::getInstance() is called, or "instances array of Singleton"? I think "array in B", did it?

– Guy Fawkes Mar 2 at 22:52 No, array in Singleton, as B doesn't have its own $_instances ... when you call B::$_instances, or static::$_instances from within B, it will reference the one in Singleton. This would only be different if you explicitly defined $_instances within B. – Jeff Parker Mar 3 at 4:19 I can not to understand ideology: "static" written in method of Singleton, so when this method calls from B, why static do not references to B?

– Guy Fawkes Mar 3 at 6:36 It does reference B, but because B doesn't include a definition of $_instances, it gets passed to the parent class, Singleton. If you add $_instances to B, then that would be different, but as it is, B only has access to $_instances because there is an instance in Singleton. One instance of $_instances, shared between all subclasses which don't have their own instance.

– Jeff Parker Mar 3 at 9:13 add "protected static $_instances = array();" to B and/or C, and re-run your example. You should see what I mean. – Jeff Parker Mar 3 at 10:14.

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