php object comparison

Object comparison in PHP 5 is more complex than in PHP 4, and the desired result is more consistent with an object-oriented language.

When using the comparison operator (==) to compare two object variables, the principle of comparison is: if the attributes and attribute values ​​​​of the two objects are equal, and the two objects are instances of the same class, then the two objects Object variables are equal.

If you use the equality operator (===), these two object variables must point to the same instance of a certain class (that is, the same object).

The above principles can be understood through the following examples.

Example #1 Object comparison of PHP 5

<?php
function bool2str($bool)
{
    if ($bool === false) {
        return &#39;FALSE&#39;;
    } else {
        return &#39;TRUE&#39;;
    }
}
function compareObjects(&$o1, &$o2)
{
    echo &#39;o1 == o2 : &#39; . bool2str($o1 == $o2) . "\n";
    echo &#39;o1 != o2 : &#39; . bool2str($o1 != $o2) . "\n";
    echo &#39;o1 === o2 : &#39; . bool2str($o1 === $o2) . "\n";
    echo &#39;o1 !== o2 : &#39; . bool2str($o1 !== $o2) . "\n";
}
class Flag
{
    public $flag;
    function Flag($flag = true) {
        $this->flag = $flag;
    }
}
class OtherFlag
{
    public $flag;
    function OtherFlag($flag = true) {
        $this->flag = $flag;
    }
}
$o = new Flag();
$p = new Flag();
$q = $o;
$r = new OtherFlag();
echo "Two instances of the same class\n";
compareObjects($o, $p);
echo "\nTwo references to the same instance\n";
compareObjects($o, $q);
echo "\nInstances of two different classes\n";
compareObjects($o, $r);
?>

The above routine will output:

Two instances of the same class
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : FALSE
o1 !== o2 : TRUE
Two references to the same instance
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : TRUE
o1 !== o2 : FALSE
Instances of two different classes
o1 == o2 : FALSE
o1 != o2 : TRUE
o1 === o2 : FALSE
o1 !== o2 : TRUE

Note:

You can define the principles of object comparison by yourself in the PHP extension.