On page 356,

(motto1 = motto2) = motto3;

If the return type is just CMessage, this will not be legal because a temporary copy of the original object is actually returned so it will be an rvalue, and the compiler will not allow a member function call using an rvalue.

However, on page 361,

// Function to add two CBox objects
CBox CBox::operator+(const CBox& aBox) const
{
// New object has larger length and width, and sum of heights
return CBox(m_Length > aBox.m_Length ? m_Length : aBox.m_Length,
m_Width > aBox.m_Width ? m_Width : aBox.m_Width,
m_Height + aBox.m_Height);
}

the function above is legal for the similar operation like,

smallBox + mediumBox + certainBox


The question is,

the explicit overloaded function call for the assignment operation is

(motto1.operator=(motto2)).operator=(motto3);


the explicit overloaded function call for the addition operator is

(smallBox.operator+(mediumBox)).operator+(certainB ox);


Is there any distinction between the two explicit overloaded function, considering they both return a temporary copy if the former's return type is CMessage？ I can't see much difference between them. But the former is not legal and the latter is legal.

Thank you!

Maybe it's wrong with “the compiler will not allow a member function call using an rvalue” because the following code is legal:

(motto1=motto2).showit(); //supposing the return type of operator=() function is CMessage

The real reason for the above question is the second assignment is done on the temporary copy if the return type is CMessage.

Is that right?

I'm working on it.