Programming PHP

The object created bythe Person constructor is copied, and the copyis stored in
$fred. This means that $this in the constructor and $fred actuallyrefer to two different
objects. If the constructor creates an alias to $this through a reference, it won’t
create an alias to $fred. For example:
$people = array();
class Person {
function Person () {
global $people;
$people[] =& $this;
}
}
$fred = new Person;
$fred->name = "Fred";
$barney =& new Person;
$barney->name = "Barney";
var_dump($people);
array(2) {
[0]=>
&object(person)(0) {
}
[1]=>
&object(person)(1) {
["name"]=>
string(6) "Barney"
}
}
$fred is a copyof the object that the constructor stored in $people[0], while $barney
is an alias for the object that the constructor stored in $people[1]. When we change
the properties of $fred, we’re not changing the object that is in $people[0]. However,
when we change the properties of $barney, we are changing the object in
$people[1].
To prevent copying on assignment, assign by reference:
$obj =& new Class;
This code makes $obj an alias for the new object, which was $this in the constructor.
If the constructor stores a reference to $this, it keeps a reference to $obj.
The documentation for a class should saywhether you need to use =& with its constructor.
In most cases, this isn’t necessary.
Introspection
Introspection is the abilityof a program to examine an object’s characteristics, such
as its name, parent class (if any), properties, and methods. With introspection, you
can write code that operates on anyclass or object. You don’t need to know which
methods or properties are defined when you write your code; instead, you can discover
that information at runtime, which makes it possible for you to write generic
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Introspection | 147