Returning *this with an assignment operator

Question

I went over making my own copy constructor and it overall makes sense to me. However, on the topic of doing your own assignment operator I need someone to fill in the blank for me.

I pretty much don't get why you are returning *this in all the examples, such as the one below:

Foo & Foo::operator=(const Foo & f)
{

//some logic

return *this;

}

So if I have some statements like:

Foo f;
f.hour = 7;

Foo g;
g = f;

Once the assignment operator runs, it returns a reference to the g object (the *this). So now the question is, won't I now have a statement implicitly like this?:

g = g (g being a reference)

The thing is, before, setting a reference to just an object would have caused the copy constructor to be invoked. In this case, it doesn't even though it fits the signature of the copy constructor.

Answer 1

You want to return *this so you can chain =:

Foo f, g, h;

f = g = h;

This is basically assigning h into g, then assigning g (returned by return *this) into f:

f = (g = h);

Another situation this is sometimes used in is having an assignment in a conditional (considered bad style by many):

if ( (f = 3).isOK() ) {

With the statement g = f; the return is just ignored, like if you did 3 + 4;.