Question

I have a project with many vectors, sets and maps. In most cases the key/index is an integer. I am considering creating small classes like:

class PhoneRepoIx //index into map {phone_number => pointer}
{
public:
  int n;
};

class PersonIx //index into map {social_security_number => pointer}
{
public:
  int n;
};

Would I incur any speed or memory penalty? With memory I am 90% sure that there would be no memory cost per instance, only per class-type. With speed I am not clear.

Motivation:
With the above approach, the compiler would do some extra type-checking for me. Also, with well chosen explicit type-names, the reader of my code will see more easily what I am doing. As of now I am using int everywhere and I chose the variable names to express what each index is. With the above, my variable names could be shorter.

Note:
Tyepdefs do not address my issue completely as the compiler would not do any extra type-checking, internally all the types would just be int.

Answer 1

Different compilers have different optimization abilities and different bugs. It is theoretically possible to compile this with precisely zero overhead. Will your compiler attain this theoretical limit? The answer is a definite “maybe”. At least some compilers are known to do it at least some of the time.

The more interesting question is whether you should be worried over a possible performance degradation. And the answer to this question is a strong “no”. Not until your program does in fact show unacceptable performance figures.