PHP: Tips and Tricks - Page 3

Variables

Dynamic Variable Names

Use the variable variable syntax by prepending a $ to a variable whose value us the variable name you want.

<?php
	$dynamic = 'number';
	$number = 1024;
	print $$dynamic; // prints 1024!
	print ' ';
	print "${'num'.'ber'}"; // prints 1024!
?>

Serialize Data Using JSON

Use the functions json_encode and json_decode to serialize arrays.

<?php
	$arr = array('first_name' => 'John', 'last_name' => 'Smith', 'age' => 25, 'address' => array('street' => '123 Abc Ln', 'city' => 'New York', 'state' => 'NY'));
	$json = json_encode($arr);
	$f = fopen('personal_info.json', 'w') or die('cannot open personal_info.json');
	fputs($f, $json);
	fclose($f) or die('cannot close personal_info.json');
	print $json;
?>

<?php
	$arr = json_decode(file_get_contents('personal_info.json'), TRUE);
	print '<pre>';
	print_r($arr);
	print '</pre>';
?>

Functions

Dynamic Functions

Define a function dynamically as the script is running.

<?php
	$x = 10;
	$volume = function($y, $z) use ($x) {
		return $x * $y * $z;
	};
	$v = $volume(5, 7);
	print $v;
?>

Variable Number of Arguments

Pass the function a single array-typed argument and put the variable arguments in the array.

<?php
	function html_bold($items) {
		$html = '';
		foreach($items as $i) {
			$html .= '<b>'.$i.'</b>';
		}
		return $html;
	}
	$arr = array('this', 'is', 'a', 'test');
	$str = html_bold($arr);
	print $str;
?>

Return Values by Reference

To return by reference place a & symbol before the name of the function. Also, use the =& operator when invoking the function.

<?php
	function &find_array_value(&$array, $search_value) {
		foreach($array as $key => $value) {
			if($search_value == $value) {
				return $array[$key];
			}
		}
	}
	$arr = array('this', 'is', 'a', 'test');
	$f =& find_array_value($arr, 'test');
	print $f;
?>

Accessing a Global Variable

Global variables can be brought into scope using the global keyword.

<?php
	function some_func() {
		global $some_var;
		$some_var++;
	}
?>

Or:

<?php
	function some_func() {
		$GLOBALS['some_var']++;
	}
?>

Classes

Access Modifiers

Use the private, protected and public keywords to control access to methods and data members.

<?php
	class Food {
		private $pasta; // available only to this class
		protected $apples; // available to this class and derived classes
		public $nuts; // available everywhere

		private function set_apples() {
			$this->apples = 4;
		}

		protected function set_nuts() {
			$this->nuts = 100;
		}

		public function set_pasta() {
			$this->pasta = 1;
		}
	}

	class Dinner extends Food {
		private $guests;

		public function set_apples() {
			$this->apples = 2; // can access the protected member of the base class
		}

		public function set_guests() {
			$this->guests = 4;
		}

		public function set_food() {
			$this->set_nuts();
		}
	}

	$f = new Food;
	$f->set_pasta(); // the only method that can be called from outside the Food class
	$f->nuts = 50; // the only member that can be accessed from outside the Food class
	$d = new Dinner;
	$d->set_apples(); // changes the apples member of the base class
	$d->nuts = 75; // can access the nuts member of the base class
	$d->set_pasta(); // can access set_pasta method of the base class
?>

Static Methods

Access methods without instantiating an object.

<?php
	class Rectangle {
		public static function area($width, $height) {
			return $width * $height;
		}
	}

	$area = Rectangle::area(65, 33);
	print $area;
?>

Abstract Base Classes

Create a class that is not directly instantiable but is a common base class for derived classes. Use the abstract keyword.

<?php
	abstract class TwoDimensional {
		abstract public function set_width($value);
		abstract public function set_height($value);
	}

	class Rectangle extends TwoDimensional {
		private $width;
		private $height;

		public function set_width($value) {
			$this->width = $value;
		}

		public function set_height($value) {
			$this->height = $value;
		}
	}
?>

Interfaces

Interaces require that classes behave in a similarly fashion. Define an interface and declare that a class implements it.

<?php
	interface RectangleInterface {
		public function set_width($value);
		public function set_height($value);
	}

	class Rectangle implements RectangleInterface {
		private $width;
		private $height;

		public function set_width($value) {
			$this->width = $value;
		}

		public function set_height($value) {
			$this->height = $value;
		}
	}
?>

Cloning Objects

When the assignment operator (=) is used with objects, it copies by reference. To copy objects by value use clone.

<?php
	class Rectangle {
		private $width;
		private $height;

		public function set_width($value) {
			$this->width = $value;
		}

		public function set_height($value) {
			$this->height = $value;
		}
	}
	$rect1 = new Rectangle;
	$rect2 = $rect1 // $rect2 points to $rect1
	$rect3 = clone $rect1; // now there are two objects
?>

Class Constants

Use const and self keywords and ::.

<?php
	class Circle {
		const pi = 3.14159;
		protected $radius;

		public function set_radius($value) {
			$this->radius = $value;
		}

		public function circumference() {
			return 2 * self::pi * $this->radius;
		}
	}
	$radius = 10;
	$area = Circle::pi * $radius * $radius;
	print $area;
	$circle = new Circle;
	$circle->set_radius(25);
	print $circle->circumference();
?>

Accessing Overridden Methods

To access a method in the base class that's overridden by the derived class, use the parent keyword.

<?php
	class Rectangle {
		protected $width;
		protected $height;

		public function set_width($value) {
			$this->width = $value;
		}

		public function set_height($value) {
			$this->height = $value;
		}

		public function area() {
			return $this->width * $this->height;
		}
	}

	class Box extends Rectangle {
		protected $depth;

		public function set_depth($value) {
			$this->depth = $value;
		}

		public function area() {
			if($this->width == $this->height && $this->width == $this->depth) {
				return parent::area() * 6; // use parent to refer to the base class
			}
		}
	}
?>

Object Stringification

Control how objects are displayed. Implement a __toString() method.

<?php
	class Rectangle {
		private $width;
		private $height;

		public function __toString() {
			return $this->width.'x'.$this->height;
		}

		public function set_width($value) {
			$this->width = $value;
		}

		public function set_height($value) {
			$this->height = $value;
		}
	}
?>

Check Which Class an Object is an Instance of

Use the instanceof keyword.

<?php
	class Rectangle {
		private $width;
		private $height;

		public function set_width($value) {
			$this->width = $value;
		}

		public function set_height($value) {
			$this->height = $value;
		}
	}
	$rect = new Rectangle;
	if($rect instanceof Rectangle) {
		print '$rect is a Rectangle';
	}
?>

Dynamic Object Instantiation

<?php
	class Rectangle {
		private $width;
		private $height;

		public function set_width($value) {
			$this->width = $value;
		}

		public function set_height($value) {
			$this->height = $value;
		}
	}
	$class_name = 'Rectangle';
	$class = new $class_name; // new Rectangle
	if($class instanceof Rectangle) {
		print '$class is a Rectangle';
	}
?>

Automatically Load Class Files when Instantiated

There is no reason to include all the class definitions in every script so use the __autoload function include only the class definitions used by the script.

<?php
	function __autoload($class_name) {
		include "$class_name.php";
	}
	$rect = new Rectangle; // this is when the Rectangle.php file will be included.
?>

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