oop tutorials

[lutger]

Saaa wrote:

>> Could anybody give a simple example of unallocated class reference use?
>> I think that would explain it all to me :)

I'll try to give a few examples.

1. Error checking:

Class theObject = tryToMakeTheObjectInASpecialWay();
if (theObject is null)
    throw new Exception("could not make the object!");

2. Conditional construction, this isn't really a good way to do it but that
doesn't matter for this example:

Car myCar;

if (winLottery == true)
    myCar = new Porsche();
else
    myCar = new Ford();

3. Composition. It is common that objects holds references to other objects
that are allocated at a later stage than that the 'parent' object is
allocated.

A classical example is a linked list:

class List(T)
{
    T data;     
    List!(T) next;
}


> Class className; // This will create a reference
> className=new Class(); // This will allocate an instance of Class
> 
> Why do I need to name the class twice?
> Is there a shortcut?

In this case you don't, it's better to write:
Class className = new Class();

or with type inference:

auto className = new Class();

> And, could I do:
> 
> Class className;
> className=new Class_2();

Yes, but only if Class_2 can be downcast to Class:

class Class_2 : Class
{
}

Again, you could also write Class className = new Class_2();