Question

In PHP, if you define a class, and then instantiate an object of that class, it’s possible to later arbitrarily add new members to that class. For example:

class foo {     public $bar = 5; }  $A = new foo; $A->temp = 10; 

However, I’d like the ability to make it impossible to add new members this way. Basically I want the class to ONLY have the members that are specified in its definition; if you try to set any other members, it fatally errors. The intent here is that I want to define a class as a very specific set of properties, and ensure that ONLY those properties exist in the class, so that the class contents are well-defined and cannot change later on (the values of each member can change, but not the members themselves).

I realize I can do this with the __set method, and simply have it fatal error if you try to set a member which doesn’t already exist, but that’s annoying to have to include in every class definition (although I could define each of my classes to extend a base class with that method, but that’s also annoying). E.g.:

class foo {     public $bar = 5;      private function __set($var, $val) {         trigger_error('Cannot dynamically add members to a class', E_USER_ERROR);     } } 

Is there any other (preferably more convenient) way to do this? Aside from modifying PHP itself to disallow this behavior?

Answer 1

No. There’s no better way than __set in a base class — yet. This is a known problem and is planned to be addressed in the future:

Introduce concept of “strict classes” that do not permit dynamic property creation