Comparing objects


In PHP 4, objects are compared in a very simple manner, namely: Two object instances are equal if they have the same attributes and values, and are instances of the same class. Similar rules are applied when comparing two objects using the identity operator (===).

If we were to execute the code in the example below:

Пример #1 Example of object comparison in PHP 4

<?php
function bool2str($bool) {
    if (
$bool === false) {
            return 
'FALSE';
    } else {
            return 
'TRUE';
    }
}

function 
compareObjects(&$o1, &$o2) {
    echo 
'o1 == o2 : '.bool2str($o1 == $o2)."\n";
    echo 
'o1 != o2 : '.bool2str($o1 != $o2)."\n";
    echo 
'o1 === o2 : '.bool2str($o1 === $o2)."\n";
    echo 
'o1 !== o2 : '.bool2str($o1 !== $o2)."\n";
}

class 
Flag {
    var 
$flag;

    function 
Flag($flag=true) {
            
$this->flag $flag;
    }
}

class 
SwitchableFlag extends Flag {

    function 
turnOn() {
        
$this->flag true;
    }

    function 
turnOff() {
        
$this->flag false;
    }
}

$o = new Flag();
$p = new Flag(false);
$q = new Flag();

$r = new SwitchableFlag();

echo 
"Compare instances created with the same parameters\n";
compareObjects($o$q);

echo 
"\nCompare instances created with different parameters\n";
compareObjects($o$p);

echo 
"\nCompare an instance of a parent class with one from a subclass\n";
compareObjects($o$r);
?>

Результат выполнения данного примера:

     Compare instances created with the same parameters o1 == o2 : TRUE o1 != o2 : FALSE o1 === o2 : TRUE o1 !== o2 : FALSE  Compare instances created with different parameters o1 == o2 : FALSE o1 != o2 : TRUE o1 === o2 : FALSE o1 !== o2 : TRUE  Compare an instance of a parent class with one from a subclass o1 == o2 : FALSE o1 != o2 : TRUE o1 === o2 : FALSE o1 !== o2 : TRUE 
Which is the output we will expect to obtain given the comparison rules above. Only instances with the same values for their attributes and from the same class are considered equal and identical.

Even in the cases where we have object composition, the same comparison rules apply. In the example below we create a container class that stores an associative array of Flag objects.

Пример #2 Compound object comparisons in PHP 4

<?php
class FlagSet {
    var 
$set;

    function 
FlagSet($flagArr = array()) {
        
$this->set $flagArr;
    }

    function 
addFlag($name$flag) {
        
$this->set[$name] = $flag;
    }

    function 
removeFlag($name) {
        if (
array_key_exists($name$this->set)) {
            unset(
$this->set[$name]);
        }
    }
}


$u = new FlagSet();
$u->addFlag('flag1'$o);
$u->addFlag('flag2'$p);
$v = new FlagSet(array('flag1'=>$q'flag2'=>$p));
$w = new FlagSet(array('flag1'=>$q));

echo 
"\nComposite objects u(o,p) and v(q,p)\n";
compareObjects($u$v);

echo 
"\nu(o,p) and w(q)\n";
compareObjects($u$w);
?>

Результат выполнения данного примера:

 Composite objects u(o,p) and v(q,p) o1 == o2 : TRUE o1 != o2 : FALSE o1 === o2 : TRUE o1 !== o2 : FALSE  u(o,p) and w(q) o1 == o2 : FALSE o1 != o2 : TRUE o1 === o2 : FALSE o1 !== o2 : TRUE