Exceptional C++: 47 Engineering Puzzles, Programming Problems, and Solutions

Chapter 38. Object Identity

Difficulty: 5

“Who am I, really?” This problem addresses how to decide whether two pointers really refer to the same object.

The “this != &other” test (illustrated below) is a common coding practice intended to prevent self-assignment. Is the condition necessary and/or sufficient to accomplish this? Why or why not? If not, how would you fix it?

T& T::operator=( const T& other ) 
{
  if( this != &other )    // the test in question
  {
    // ...
  }
  return *this;
}

Remember to distinguish between “protecting against Murphy versus protecting against Machiavelli”—that is, protecting against things going wrong on their own versus a malicious programmer going to great lengths trying to break your code.

Solution

Short answer: In most cases, ...