PHP Tips - 'Dynamic' Calling of Static Classes |Tech Lull

Suppose you want to dynamically call a static function because you don't know ahead of time which one you will need. For instance, you might have two subclasses of a base class. If they were normal classes you could easily do this using a variable string an instance creation or polymorphism.


$instance = new $which_class();

The same does not hold true for static classes. However, on the zend.com forums page, I got this solution which uses the eval() function. Now, I normally do not use the eval() function because it has some security risks, etc. But, it is very useful in this case. FYI, I came across this problem when trying to dynamically select a registry class which was based on a singleton pattern.


class A
{
    public static function instance(){
    }
}

class B
{
    public static function instance(){
    }
}

$obj_type = 'A';
$instance = eval("return {$obj_type}::instance();");

One final note is that you must include return in the function argument if you wish to return a value, and not just evaluate a statement.

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'Dynamic' Calling of Static Classes