[cs13001] Questions about keyword 'this'

[Mikhail Nesterenko]

> 
> The slide says this is a pointer to the object that invokes the member
> function.  What does it point to specifically?
> 

It points to the object itself. That is, "this" holds the address of
the object on which the member function is invoked.

>  
> 
> So we're making sure the address for the calling object isn't the same
> memory location of the object passed to the function.
> 

This check is done to prevent self-assignment of the kind below
from destroying the object in the overloaded assignment

  object1 = object1; // self-assignment


> If it is, why do we return the data from the location this is pointing to
> instead of leaving it alone?  Is it because we have to return an object of
> MyClass?  Are we assigning it to itself?
> 

The return value of the assignment is used to implement stackability:

   object1 = object2 = object3;

Assignment is evaluated from right to left. That is, first 

(object2 = object3)

expression is evaluated. Its value is then assigned to object1 And, as
defined below, the value of (object2 = object3) expression is object2,
which is assigned to object1.

Thanks,
--
Mikhail

> 
> MyClass& MyClass::operator= (const MyClass& rhs){
>    if (this != &rhs){ // if not same
>       size=rhs.size;
>       delete [] d;
>       d=new int[size];
>       for (int i=0; i < size; i++)
>          d[i]=rhs.d[i];
>    }
>    return *this; // return lhs
> }