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PHP Objects and references
Introduction
In PHP, objects are passed by references by default. Here, reference is an alias, which allows two different variables to write to the same value. An object variable doesn't contain the object itself as value. It only contains an object identifier which allows using which the actual object is found. When an object is sent by argument, returned or assigned, the different variables are not aliases − instead, they hold a copy of the identifier, pointing to the same object.
Example
PHP has spl_object_hash() function that returns unique hash ID of an object. In following code, two object variables, referring to same object return same ID
Example
<?php
class test1{
public $name;
}
$obj1=new test1();
echo "ID of obj1: " . spl_object_hash($obj1) . "
";
$obj2=$obj1;
echo "ID of obj2: " . spl_object_hash($obj2);
?>Output
Result shows ID of both variables is same
ID of obj1: 000000004355dda6000000006f04b1a7 ID of obj2: 000000004355dda6000000006f04b1a7
When we create a reference of an object variable, by prefixing & to name, any changes in the properties are automatically reflected in reference variable
Example
<?php
class test1{
public $name;
}
$obj1=new test1();
echo "ID of obj1: " . spl_object_hash($obj1) . "
";
$obj2=&$obj1;
echo "ID of obj2: " . spl_object_hash($obj2) . "
";
$obj1->name="Amar";
echo "name: " .$obj2->name;
?>Output
Above code now returns name following output
ID of obj1: 00000000163cf0b8000000003ad0ed93 ID of obj2: 00000000163cf0b8000000003ad0ed93 name: Amar
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