Constructors
Constructors are functions in a class that are automatically called when you create a new instance of a class with new. A function becomes a constructor, when it has the same name as the class. If a class has no constructor, the constructor of the base class will be called, if it exists.
<?php
class Auto_Cart extends Cart {
function Auto_Cart() {
$this->add_item("10", 1);
}
}
?>
This defines a class Auto_Cart that is a Cart plus a constructor which initializes the cart with one item of article number "10" each time a new Auto_Cart is being made with "new". Constructors can take arguments and these arguments can be optional, which makes them much more useful. To be able to still use the class without parameters, all parameters to constructors should be made optional by providing default values.
<?php
class Constructor_Cart extends Cart {
function Constructor_Cart($item = "10", $num = 1) {
$this->add_item ($item, $num);
}
}
// Shop the same old boring stuff.
$default_cart = new Constructor_Cart;
// Shop for real...
$different_cart = new Constructor_Cart("20", 17);
?>
You also can use the @ operator to mute errors occurring in the constructor, e.g. @new.
<?php
class A
{
function A()
{
echo "I am the constructor of A.<br />\n";
}
function B()
{
echo "I am a regular function named B in class A.<br />\n";
echo "I am not a constructor in A.<br />\n";
}
}
class B extends A
{
}
// This will call B() as a constructor
$b = new B;
?>
The function B() in class A will suddenly become a constructor in class B, although it was never intended to be. PHP 4 does not care if the function is being defined in class B, or if it has been inherited.
PHP doesn't call constructors of the base class automatically from a constructor of a derived class. It is your responsibility to propagate the call to constructors upstream where appropriate.
Destructors are functions that are called automatically when an object is destroyed, either with unset() or by simply going out of scope. There are no destructors in PHP. You may use register_shutdown_function() instead to simulate most effects of destructors.
Коментарии
"There are no destructors in PHP. You may use register_shutdown_function() instead to simulate most effects of destructors. "
I thought this was a particularly strange statement, seeing as that I use __construct() en __destruct() the whole time. And surely, from language.oop5.decon we can read this:
"void __destruct ( void )
PHP 5 introduces a destructor concept similar to that of other object-oriented languages, such as C++. The destructor method will be called as soon as there are no other references to a particular object, or in any order during the shutdown sequence. "
And even:
"The destructor will be called even if script execution is stopped using exit(). Calling exit() in a destructor will prevent the remaining shutdown routines from executing."
So PHP definitely supports destructors.
I only just noticed this page is specifically referring to PHP 4, so I'd suggest changing"There are no destructors in PHP."
to
"There are no destructors in PHP 4. Support for destructors was added in PHP 5."