OOP Practice

PHPGuru2

Which one is the better way of using an object?

class A
{
$db = new database;
...
...
function connect_db()
{
this->db->connect_db();
}
}

class A extends database
{
...
...

function connect_db()
{
this->connect_db();
}
}

The first one instanciates a database object and use it in the method to connect to db so A can update/delete/insert data.

The second one extends the database class so class A inherits all from the parent class, database.

The only different I can see is that when you extend a class with another, then the extended one can do much more flexible things and you can also instanciate as many as objects you want within the class (oppose to extend multiple classes.)

axo

the second version is definitely the better way, because you even don't need to make a new method connect_db(), because the child class inherits it from its parent.

so, you only will have to 'overwrite' (overload, correctly spoken) connect_db() if the child class makes somewhat different from the parent method.

ahundiak

In general, you should only extend a class if there is a "IS A" relationship between the parent and the child. In other words, if class A "IS A" database abstraction class then by all means extend database.

But if class A represents something different (such as a person) then your first example is a better oop design.

Weedpacket

Originally posted by ahundiak
But if class A represents something different (such as a person) then your first example is a better oop design.

But I'll point out that it might not be a good idea to instantiate the database in the class definition; rather, just declare a var for it and instantiate it in class A's constructor.

PHPGuru2

But I'll point out that it might not be a good idea to instantiate the database in the class definition; rather, just declare a var for it and instantiate it in class A's constructor.

What is the reason for this? Is it supposed to mess up something when class is instanciated and instanciated class instanciates something inside?? For example:

class A
{
     var $db;

 // Constructor - instanciates a database class
 function A() { $this->db = new database; }
 .....
 .....
}

It this a bad idea? I haven't tried this yet but I will soon though.

Another question, what's the difference between the class above and the first one from the original thread?

Is there a difference between instanciating a class when class is defined and instanciating a class within a constructor (a class is instanciated and that class instanciates some other class in it's constructor)??

Does anyone have answer for this?

class A

illusion

Puttin new database in constructor is someday you may change your bussiness rules, you've got the flexibility of changing it if it is in the constructor

e.g

class A
{
var $db;

 // Constructor - instanciates a database class 
 function A() { $this->db = new database; }

}

can change to...

class A
{
var $db;

 // Constructor - instanciates a database class 
 function A() { 
    $this->db = new database; 
    if ($this->db->username=="")  $this->db = null; 
    //for whatever purpose
 }

}