The second is pretty standard. You often prefer to return a reference from an assignment operator so that statements like a = b = c;
resolve as expected. I can't think of any cases where I would want to return a copy from assignment.
One thing to note is that if you aren't needing a deep copy it's sometimes considered best to use the implicit copy constructor and assignment operator generated by the compiler than roll your own. Really up to you though ...
Edit:
Here's some basic calls:
SimpleCircle x; // default constructor
SimpleCircle y(x); // copy constructor
x = y; // assignment operator
Now say we had the first version of your assignment operator:
SimpleCircle SimpleCircle::operator=(const SimpleCircle & rhs)
{
if(this == &rhs)
return *this; // calls copy constructor SimpleCircle(*this)
itsRadius = rhs.getRadius(); // copy member
return *this; // calls copy constructor
}
It calls the copy constructor and passes a reference to this
in order to construct the copy to be returned. Now in the second example we avoid the copy by just returning a reference to this
SimpleCircle & SimpleCircle::operator=(const SimpleCircle & rhs)
{
if(this == &rhs)
return *this; // return reference to this (no copy)
itsRadius = rhs.getRadius(); // copy member
return *this; // return reference to this (no copy)
}