Please tell me in C how does return this relates to returning a reference in assignment operator overloading I am confused because this is a pointer and Myclass is a reference.?

Answer 1

The this pointer is a constant pointer which stores the address of the current instance of Myclass. There are three values associated with the this pointer:

&this : the address of the thispointer

this : the address of the current instance of Myclass

*this : the dereferenced value of the current instance of Myclass

Since *this is the dereferenced value of this, when a function needs to return a reference it will automatically return this value by reference.

Thus for a Myclass class with the following definition:

class Myclass {

private:

int attribute;

public:

Myclass& operator= (const Myclass&);

};

The implementation of the assignment operator would be:

Myclass& Myclass::operator= (const Myclass& rhs)

{

attribute = rhs.attribute;

return *this;

}

The implementation might be clearer if you implement it this way:

Myclass& Myclass::operator= (const Myclass& rhs)

{

Myclass& result = *this; // directly refer to this instance.

result.attribute = rhs.attribute;

return result;

}

In the above example, *this (the dereferenced value of this) is assigned to the reference named result. Since result is a reference (not a variable), resultrefers to the same instance pointed to by this.

Thus,

result.attribute = rhs.attribute;

is exactly the same as if we'd said

this->attribute = rhs.attribute;

// or, attribute = rhs.attribute;

and

return result;

is the same as if we'd said

return *this;

Note that since we already have a pointer (this), we do not need a reference as well. We gain nothing by using a direct reference in this way. Of course it would have made more sense had the this pointer been implemented as a reference rather than a pointer, however C++ evolved from C and C has no concept of a distinct reference type. Thus the earliest implementations of C++ used pointers just like C. References were added much later and to switch to references now would require a fundamental change to C++ that would literally break billions of lines of code, especially every single return *this; statement.