PHP Compare Objects

Summary: in this tutorial, you will learn how to compare objects in PHP using comparison operator ( ==) and identity operator ( ===).

Let’s create a new class for demonstration.

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<?php class Point{ private $x; private $y;   public function __construct($x,$y){ $this->x = $x; $this->y = $y; }   public function setX($x){ $this->x = $x; } public function getX(){ return $this->x; }   public function setY($y){ $this->y = $y; } public function getY(){ return $this->y; }   }

The Point class has two properties:  $x coordinate and  $y coordinate.

Comparing objects using comparison operator (==)

When we compare objects using comparison operator ( ==), two objects are equal if they are the instances of the same class and have the same properties and values.

Let’s add a static method to compare two Point objects:

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/** * Compare two points * @param Point $p1 * @param Point $p2 * @return boolean return true if two points are equal, otherwise returns false */ public static function compare($p1,$p2){ return $p1 == $p2; }

Now, we create two new objects with the same properties’ values and compare them:

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$p1 = new Point(10,20); $p2 = new Point(10,20);   if(Point::compare($p1, $p2)){ echo 'p1 and p2 are equal <br/>'; } else{ echo 'p1 and p2 are not equal <br/>'; }

Two Points are equal.

We can assign  $p2 to a new reference $p3, both  $p2 and  $p3 are pointing the the same object.

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$p3 = $p2; if(Point::compare($p2, $p3)){ echo 'p2 and p3 are equal <br/>'; } else{ echo 'p2 and p3 are not equal <br/>'; }

$p2 and  $p3 are equal as well.

Now we can create a new point object with different properties’ values and compare it with $p3:

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$p4 = new Point(20,10); if(Point::compare($p3, $p4)){ echo 'p3 and p4 are equal <br/>'; } else{ echo 'p3 and p4 are not equal <br/>'; }

$p3 and  $p4 are not equal.

Comparing objects using identity operator (===)

When you use the identity operator to compare objects, they are identical if and only if both of them refer the the same instance of class.

The following  $p1 and  $p2 objects are identical when we use identity operator ( ===) to compare because they are all refer to the same object.

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<?php $p1 = new Point(10,20); $p2 = $p1;   if($p1 === $p2){ echo '$p1 and $p2 are identical'; }else{ echo '$p1 and $p2 are not identical'; }

However the following  $p3 object is not identical to the  $p1 even their properties values are the equal.

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$p3 = new Point(10,20); if($p1 === $p3){ echo 'p1 and p3 are identical'; }else{ echo 'p1 and p3 are not identical'; }