LinuxQuestions.org - C++ containment

I dont quite understand why the + operator can't be called within the following statement
String buffer Edie.GetFirstName() + Edie.GetLastName();

Edie is an employee object which uses the following string class

code for + operaotor within string class

PHP Code:




String String::operator+(const String&  rhs)

--the rest of the code are assignment statments which dont change rhs--

The GetFirstName returns a constant string which is what the function accepts as a parameter. The book said in order to fix this I would have to overload the GetFirstName to be non const because u cant use the + operator on a constant object which is returned by GetFirstName.

const String & GetFirstName() const

is it because u cant have a constant pointer to a constant object?