PHP Class instanced twice even with Singleton design pattern - php

Question

Class:
if( ! class_exists('MY_CLASS') ) :
class MY_CLASS {
private static $_instance = null;
private static $counter = 0;
private function __construct() {
self::$counter++;
// Do stuff here.
echo "instances: " . self::$counter . "<br>";
}
// Other functions here
public static function instance() {
if ( is_null( self::$_instance ) ) {
self::$_instance = new MY_CLASS();
}
return self::$_instance;
}
}
function ctp() {
return MY_CLASS::instance();
}
// initialize
ctp();
endif; // class_exists check
The $counter is always 2. I've checked and the function instance() enters the if condition is_null( self::$_instance ) twice.
Really not being able to make this class only be instanced once. Please help.

Answer 1

Sorry, found what was causing the problem.
So in My_Class I had:
function includes() {
require_once( 'path-to-second-class.php' );
// several other requires
}
private function init() {
// various class instantiations « new Class_Name() », but not for Second_Class
}
And in second-class.php I had
class Second_Class {
$taxs = array();
function __construct() {
$this->taxs = ctp()->get_ctp_taxs(); // which returns Main_Class->$taxs
// do other stuff
}
function do_stuff() {
foreach( $this->taxs as $tax_name => $tax_object ) {
// do stuff
}
}
}
new Second_Class();
This, for some reason that I tbh don't know, doesn't work so I changed it to:
My_Class:
function includes() {
require_once( 'path-to-second-class.php' );
// several other requires
}
private function init() {
// same other instantiations
new Second_Class();
}
And in second-class.php I now have:
class Second_Class {
function __construct() {
// do same other stuff
}
function do_stuff() {
foreach( ctp()->get_ctp_taxs() as $tax_name => $tax_object ) {
// do stuff
}
}
}