Does the C++ Arrow Operator (->) return an lvalue in all cases?

According to the C++ Primer book, "The arrow operator requires a pointer operand and yields an lvalue". Is that always the case? For example:

#include<iostream>
#include<string>

using std::string; using std::vector;

int main()
{
     vector<string> temp {"aaa", "bbb", "ccc"};
     vector<string>::iterator iter_str = temp.begin();
     bool result = iter_str->empty();  //the result of iter_str->empty() is not an lvalue right?

     return 0;
}

• When we take the expression iter_str->empty() for instance it can't be the left hand operand of an assignment operator right?
• And if the arrow operator returns an lvalue does it not have to, at all times? Or are there exceptions to this rule?