Programming PHP

These arguments are passed to the class’s constructor, a special function that initializes
the properties of the class.
A constructor is a function with the same name as the class in which it is defined.
Here’s a constructor for the Person class:
class Person {
function Person ($name, $age) {
$this->name = $name;
$this->age = $age;
}
}
PHP does not provide for an automatic chain of constructors; that is, if you instantiate
an object of a derived class, onlythe constructor in the derived class is automaticallycalled.
For the constructor of the parent class to be called, the constructor in
the derived class must explicitlycall the constructor. In this example, the Employee
class constructor calls the Person constructor:
class Person {
var $name, $address, $age;
function Person($name, $address, $age) {
$this->name = $name;
$this->address = $address;
$this->age = $age;
}
}
class Employee extends Person {
var $position, $salary;
function Employee($name, $address, $age, $position, $salary) {
$this->Person($name, $address, $age);
$this->position = $position;
$this->salary = $salary;
}
}
References
When you assign an object to another variable, you create a copy:
$fred = new Person;
$copy = $fred;
$fred->name("Fred");
print $copy->name(); // does not print "Fred"
You now have two Person objects, $fred and $copy, with independent propertyvalues.
This is also the case when you assign the results of a call to a constructor, as
shown here:
$fred = new Person;
146 | Chapter 6: Objects
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