Question

I’m studying this code:
http://www.w3style.co.uk/a-lightweight-and-flexible-front-controller-for-php-5

In it the author uses a static function to instantiate a class. I’m basically a beginner and I had never seen this. Why would one use a static instantiator rather than the usual constructor?

Here is the code:
index.php

<?php
define("PAGE_DIR", dirname(__FILE__) . "/pages");
require_once "FrontController.php";
FrontController::createInstance()->dispatch();

FrontController.php

<?php
class FrontController {
  public static function createInstance() {
    if (!defined("PAGE_DIR")) {
      exit("Critical error: Cannot proceed without PAGE_DIR.");
    }
    $instance = new self();
    return $instance;
  }
  public function dispatch() {....} 

Answer 1

This is a workaround for PHP, since it is too dumb for stuff like this:

(new SomeClass())->doSomething();

Oneliners like that are impossible in native PHP. That is why some people wrap the instantiation of the class in a static method to make it possible:

SomeClass::create()->doSomething();

It helps to keep the scope clean, since you do not need extra variables. It would look like this, otherwise:

$instance = new SomeClass();
$instance->doSomething();
unset($instance);

EDIT: let me quote Gordon here (from the comments):

Static calls are the same as putting a function into the global
scope. Calling it will always have a dependency on the global scope.

You should be aware of this fact, as it makes your code less flexible.