Sometimes we might wish to extend a third party class that has been defined as "final". 

In this example, the a child class will extend a "final" class, adding a method. An object instance will be able to access parent members, and is recognized as an instance of both the dynamically created child class as well as its parent class.

<?php
declare(strict_types=1);

/*
 *  Final class would normally prevent extending.
 */
final class ParentC
{
    public $parentvar;
    public $secondvar;
    
    function __construct() { echo( "\r\n<br/>".$this->parentvar = 'set by '.get_class().'->parentconstruct' ); }
    function parentf() { echo( "\r\n<br/>".get_class().'->parentf >> '.$this->parentvar ); }
}

/*
 *  Dynamically define a child class "DynamicC" 
 *  which successfully extends final class "ParentC".
 */
$DefC = new \Componere\Definition( 'DynamicC', 'ParentC');

// Extend child class with method 'DynamicC::dynamicf()'.
$DefM = new Componere\Method( function( $parm = null ) {
    // Populate a parent class property.
    $this->secondvar = empty( $parm ) ? 'set by '.get_class().'->dynamicf' : $parm;
    // Access an inherited property set by parent constructor.
    echo( "\r\n<br/>".get_class().'->dynamicf >> '.$this->parentvar ); 
} );
$DefC->addMethod( 'dynamicf', $DefM );

// Take dynamic child class 'life'.
$DefC->register();

/*
 *  Instantiate the dynamic child class,
 *  and access its own and inherited members.
 */

$dyno = new DynamicC;
$dyno->parentf();
$dyno->dynamicf( 'myvalue ');

// Our object is also recognized as instance of parent!
var_dump( $dyno instanceof DynamicC, $dyno instanceof ParentC );
var_dump( $dyno ); 
%>

will output:

set by ParentC->parentconstruct 
ParentC->parentf >> set by ParentC->parentconstruct 
DynamicC->dynamicf >> set by ParentC->parentconstruct

(boolean) true
(boolean) true

object(DynamicC)
  public 'parentvar' => string 'set by ParentC->parentconstruct' (length=31)
  public 'secondvar' => string 'myvalue ' (length=8)

＋add a note