This post covers the Instantiation section of the OOP chapter when studying for the Zend PHP 7 Certification.
Object-oriented programming is a style of coding that allows developers to group similar tasks into classes. This allows code to be easily maintained and you can re-use code from classes without the need of duplication.
Objects can be created by using the new statement which will instantiate a new class.
<?php
class MyClass {
}
$object = new MyClass();An object will always be created unless the object has a constructor defined that throws an exception on error.
To instantiate an empty generic PHP object, you can simply write: $object = new stdClass().
You can also cerate stdClass objects with some properties and values by casting an array as an object.
<?php
$object = (object) [
'propertyOne' => 'foo',
'propertyTwo' => 42,
];A class is a template in which objects are made. Basic class definitions begin with the keyword class, followed by a class name, followed by a pair of curly braces which enclose the definitions of the properties and methods belonging to the class.
If the class is in a namespace, its fully qualified name must be used when doing this.
<?php
namespace somenamespace;
class MyClass {
function foo() {
return __FUNCTION__;
}
}
$class = new \somenamespace\MyClass;
echo $class->foo(); // Outputs: fooThe class name can be any valid label, provided it is not a PHP reserved word. A valid class name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.
<?php
class MyClass {
}In PHP 7 there are a few ways to create an empty object.
$obj1 = new \stdClass; // Instantiate stdClass object
$obj2 = new class{}; // Instantiate anonymous class
$obj3 = (object)[]; // Cast empty array to object
var_dump($obj1); // object(stdClass)#1 (0) {}
var_dump($obj2); // object(class@anonymous)#2 (0) {}
var_dump($obj3); // object(stdClass)#3 (0) {}$obj1 and $obj3 are the same type, but they are not identical (i.e. $obj1 !== $obj3).
All three objects will output a simple JS object, {}, using json_encode().
echo json_encode([
new \stdClass,
new class{},
(object)[],
]);
// Outputs: [{},{},{}]Objects can be converted into strings using the __toString() magic method.
class MyObject {
public function __toString() {
return "Testing";
}
}
$obj = new MyObject;
echo $obj; // Outputs: TestingAn object copy is created by using the clone keyword (which calls the object’s __clone() method if possible). An object’s __clone() method cannot be called directly.
$copy_of_object = clone $object;Should you need to store an object’s data, the serialize() function gives you the ability to do so.
When serialising objects, PHP will attempt to call the member function __sleep() prior to serialisation. This is to allow the object to do any last minute clean-up, etc. prior to being serialised.
<?php
class MyObject {
}
$obj = new MyObject();
echo serialize($obj); // Outputs: O:8:"MyObject":0:{}<?php
class MyObject {
public $integer = 3;
}
$obj = new MyObject();
echo serialize($obj); // Outputs: O:8:"MyObject":1:{s:7:"integer";i:3;}The anatomy of a serialised value is described below.
Likewise, unserialize() will restore the object, and __wakeup() will attempt to be called.
A class may contain its own constants, variables (called “properties”), and functions (called “methods”).
<?php
class MyClass
{
// Property declaration
public $var = 'a default value';
// Method declaration
public function displayVar() {
echo $this->var;
}
}
$class = new MyClass();
$class->displayVar(); // Prints out 'a default value'You may notice the use of the $this keyword. The pseudo-variable $this is available when a method is called from within an object context. $this is a reference to the calling object.
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Note: This article is based on PHP version 7.0.