Edit Report a Bug

    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:

    Example #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);
    ?>

    위 예제의 출력:

        
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.

    Example #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);
    ?>

    위 예제의 출력:

    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

    add a note add a note

    User Contributed Notes

    There are no user contributed notes for this page.
    To Top