PHP: Access static function / method with object property

Question

While I understand that static methods can be invoked through a variety of approaches, such as:

A::staticFunction();

OR

$class = 'A';
$class::staticFunction();

OR

$a = new A(); // Assume class has been defined elsewhere
$a->staticFunction();

However, could someone please explain why the following won't work, and if possible, how to make this work (without resorting to the solution provided):

// Assume object $b has been defined & instantiated elsewhere
$b->funcName::staticFunction(); // Where funcName contains the string 'A'

This produces the following PHP parse error:

Parse error: syntax error, unexpected '::' (T_PAAMAYIM_NEKUDOTAYIM)

Typical working solution (follows second approach) (preferably avoid if possible):

// Assume object $b has been defined & instantiated elsewhere
$funcName = $b->funcName; // Where funcName contains the string 'A'
$funcName::staticFunction();

Answer 1

The :: operator is used to refer to a non-instanced class. That means you're referencing either static methods or variables, or const. The hallmark of static methods is that they cannot work with your instance. They are, essentially, stand-alone functions and cannot use $this to refer back to the instance of your class.

As such, you cannot refer to a static method by referencing the instance. You need to use

self::function();

or

$this->function();

While the latter makes it look like it might be part of the instance, it's included for completeness only.