c++ - How can I better learn to "not pay for what you don't use"?

Question

I've just gotten answers to this question which, at the bottom line, tell me: "Doing X doesn't make sense since it would make you pay for things you might not use."

I find this maxim difficult to follow; my instincts lean more towards seeing what I consider clear semantics, with things defined "in their place". More generally, it's not immediate for me to realize what the hidden costs and secret tariffs would be for a particular design choice?.

Is this covered by (non-reference) books on C++? Is there someplace relevant online to better enlighten myself on following this principle?

Answer 1

In the case you are presenting it is not as general a statement as it seems.

Doing X doesn't make sense since it would make you pay for things you might not use.

This is merely a statement that if you can, avoid using virtual functions. They add overhead to the function call.

Virtual functions can often be redesigned by using templates and regular function calls. One std:: example is std::vector. In Java for instance a Vector implements interfaces to be usable in algorithms. Accomplished by virtual function calls. std::vector uses iterators.