Why not have all the functions as virtual in C++?

Question

I know that virtual functions have an overhead of dereferencing to call a method. But I guess with modern architectural speed it is almost negligible.

1. Is ther

Answer 1

But I guess with modern architectural speed it is almost negligible.

This assumption is wrong, and, I guess, the main reason for this decision.

Consider the case of inlining. C++’ sort function performs much faster than C’s otherwise similar qsort in some scenarios because it can inline its comparator argument, while C cannot (due to use of function pointers). In extreme cases, this can mean performance differences of as much as 700% (Scott Meyers, Effective STL).

The same would be true for virtual functions. We’ve had similar discussions before; for instance, Is there any reason to use C++ instead of C, Perl, Python, etc?