Chaining PHP methods

Many frameworks these days allow for elegant 'chaining' of methods. This typically looks similar to $this->db->get()->users(); Want to know how to do this? we will show you how in the steps below.

Final Result

class Shape {

/**
* Name.
*
* @var string
*/
public $name = 'square';

/**
* Color.
*
* @var string
*/
public $color = 'black';

/**
* Width in pixels.
*
* @var int
*/
public $width = 0;

/**
* Height in pixels.
*
* @var int
*/
public $height = 0;

/**
* Set the shape name.
*
* @param string $name
*/
public function setName($name) {
$this->name = $name;

return $this;
}

/**
* Set the shape color.
*
* @param string $color
*/
public function setColor($color) {
$this->color = $color;

return $this;
}

/**
* Set the shape dimensions.
*
* @param int $width
*
* @param int $height
*/
public function setDimensions($width, $height) {
$this->width = $width;
$this->height = $height;

return $this;
}

/**
* Display our object.
*/
public function display() {
echo @<<
Name: {$this->name}

Color: {$this->color}

Dimensions: {$this->width}px x {$this->height}px
DISPLAY;
}
}

$rectangle = new Shape();
$rectangle->setName('rectangle')->setColor('red')->setDimensions(100, 500)->display();

?>

First off we simply set the default values for a generic shape object. Then we provide several methods such as the one below, which simply assign a variable to the corresponding property. This could be done with public properties such as $rectangle->name = 'rectangle'. However this is to demonstrate chainable methods.

Each method which is mutative (modifies the object), and which does not need to return a specific value, could potentially be chainable, simply by returning its-self (return $this).

public function setName($name) {
$this->name = $name;

return $this;
}
?>

We then need a quick method to display our object. the '@<<<' syntax below may look intimidating, this is called heredoc, which is comparable to a simple string using double quotes "".

The '@' character suppresses notices if a variable is not present such as if I were to try and output $this->nothingHere. '<<

You also may be wondering why the variables are surrounded with curly braces; {$this->color} rather than $this->color. When parsing a string such as "This product costs $$dollars", the interpreter will attempt to figure out what is a variable, and what is simply supposed to be text. By typing "This product costs ${$dollars}" we are explicitly stating that chunk of text should be replaced with a variable, saving the interpreter from doing these searches.

public function display() {
echo @<<
Name: {$this->name}

Color: {$this->color}

Dimensions: {$this->width}px X {$this->height}px
DISPLAY;
}
?>

We can now test out our code by creating an instance of our shape class.
Then invoke each method accordingly.

$rectangle = new Shape();
$rectangle->setName('rectangle')->setColor('red')->setDimensions(100, 500)->display();
?>

Since the display() method simply outputs a string, and does not return anything, if it were to be placed at the beginning or in the middle of these other methods, the following methods would not fire, because the object was not returned.

That is all! enjoy.