PHP OOP $this Keyword

$this is a pseudo-variable (also a reserved keyword) which is only available inside methods. And, it refers to the object of the current method.

Let's create a House class with one property (color). Then, create an object from it.

<?php
class House {
	public $color = 'black';
}
$house = new House();

Where to use $this?

How can we change the value of $color? Take some time and think.

There are two ways.

1. Outside the class. We can directly change the value of a property from outside of the class.

   
   $house -> color = 'white';
   
   

2. Inside the class. We can define a method in the class and call it to change the value of its own property.

   
   public function changeColor() {
   	$this -> color = 'white';
   }
   
   

   
   $house -> changeColor();
   
   

In the second way, we use $this variable to access the current object. Here, the current object is the object saved in $house.

More Examples

Let's play with the $this pseudo-variable.

Here we will create two houses and assign names and colors to them. Then, we will echo it out.

1. Create the House class

   
   <?php
   class House {
   	public $name;
   	public $color;
   	public function setData($name, $color) {
   		$this -> name = $name;
   		$this -> color = $color;
   	}
   	public function echoData() {
   		echo "The color of the {$this -> name} is {$this -> color}";
   	}
   }
   
   

2. Create two objects from it

   
   $blackHouse = new House();
   $whiteHouse = new House();
   
   

3. Call the setData method with two arguments

   
   $blackHouse -> setData("John's House", "black");
   $whiteHouse -> setData("Pearl's House", "white");
   
   

4. Call the echoData to echo out a descriptive phrase

   
   $blackHouse -> echoData();
   echo '<br>';
   $whiteHouse -> echoData();
   
   

Here's the full code.

<?php
class House {
	public $name;
	public $color;
	public function setData($name, $color) {
		$this -> name = $name;
		$this -> color = $color;
	}
	public function echoData() {
		echo "The color of the {$this -> name} is {$this -> color}";
	}
}

$blackHouse = new House();
$whiteHouse = new House(); // this is a small house, not america's one ;)

$blackHouse -> setData("John's House", "black");
$whiteHouse -> setData("Pearl's House", "white");
 
$blackHouse -> echoData();
echo '<br>';
$whiteHouse -> echoData();

Conclusion

We could access the current object with $this keyword. But, we needed to run two steps of code to create a object ($house = new House()) and set its data ($house -> setData(...)). What if we could set the data when we create the object? We can run a constructor function when the object is created. You can learn more in the next chapter.