How to clone object to child class in php

Question

I have a parent class A, and child class B in PHP. Is there any way to clone instance of class A to instance of B, and to use B class properties later in B instance?

I don't think you can extend instances in real time if that is what you are asking. Consider giving more details about what you are trying to do though, perhaps there is another way. — Mahn
– Mahn, Commented Oct 14, 2012 at 12:47
Does this answer your question? How do you copy a PHP object into a different object type — Melebius
– Melebius, Commented Jul 7, 2022 at 6:37
For those looking for answers to this question, here are the best answers - stackoverflow.com/questions/41958315/… — tecdoc ukr net
– tecdoc ukr net, Commented Jan 21, 2024 at 17:19

Community · Accepted Answer · 2017-05-23 12:24:19Z

25

My solution will be based on the solution from this question How do you copy a PHP object into a different object type

class childClass extends parentClass
{
    private $a;
    private $b;

    function loadFromParentObj( $parentObj )
    {
        $objValues = get_object_vars($parentObj); // return array of object values
        foreach($objValues AS $key=>$value)
        {
             $this->$key = $value;
        }
    }
}

$myParent = new parentClass();
$myChild = new childClass();
$myChild->loadFromParentObj( $myParent );

edited May 23, 2017 at 12:24

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answered Nov 8, 2012 at 22:35

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Comments

tecdoc ukr net · Accepted Answer · 2025-01-30 12:54:42Z

1. Simple option to understand. But in case of changes in ParentClass properties, there is a possibility of "missing" the corresponding changes in ChildClass

<?php
class ParentClass {
    public function __construct (
        public string $propParent1,
        public string $propParent2,
    ) {}
}

class ChildClass extends ParentClass{
    public string $propChild;
    
    public static function createFromParentClass(ParentClass $parentObj): ChildClass
    {
        // there is a possibility of "missing" the changes in ParentClass
        $instance = new static(
            $parentObj->propParent1, 
            $parentObj->propParent2
        );
        
        $instance->propChild = substr($instance->propParent1, 0, 5);
        
        return $instance;
    }
}

$parentObj = new ParentClass('Parent property', 'test');
$childObj = ChildClass::createFromParentClass($parentObj);
var_dump($parentObj);
var_dump($childObj);

2. The cloneParentClass pseudo-cloning method is used. All changes to the ParentClass properties are processed immediately in this class.

<?php
class ParentClass {
    public function __construct (
        public string $propParent1,
        public string $propParent2,
    ) {}
    
    /*Fatal error: Declaration of ChildClass::createFromParentClass(ParentClass $parentObj): ChildClass must be compatible with ParentClass::createFromParentClass(ParentClass $parentObj): static in /home/user/scripts/code.php on line 22
    */
    //public static function createFromParentClass(self $parentObj): static        
    public static function cloneParentClass(self $parentObj): static
    {
        // повне дублювання clone
        $instance = new static(
            $parentObj->propParent1,
            $parentObj->propParent2
        );
        return $instance;
    }
}


class ChildClass extends ParentClass{
    public string $propChild;
    
    public static function createFromParentClass(ParentClass $parentObj): ChildClass
    {
        $instance = parent::cloneParentClass($parentObj);
        $instance->propChild = substr($instance->propParent1, 0, 5);
        return $instance;
    }
}

$parentObj = new ParentClass('Parent property', 'test');
$childObj = ChildClass::createFromParentClass($parentObj);

var_dump($parentObj);
var_dump($childObj);

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