Why should virtual functions not be used excessively?

Question

I just read that we should not use virtual function excessively. People felt that less virtual functions tends to have fewer bugs and reduces maintenance.

What kind of b

Answer 1

Every dependency increases complexity of the code, and makes it more difficult to maintain. When you define your function as virtual, you create dependency of your class on some other code, that might not even exist at the moment.

For example, in C, you can easily find what foo() does - there's just one foo(). In C++ without virtual functions, it's slightly more complicated: you need to explore your class and its base classes to find which foo() we need. But at least you can do it deterministically in advance, not in runtime. With virtual functions, we can't tell which foo() is executed, since it can be defined in one the subclasses.

(Another thing is the performance issue that you mentioned, due to v-table).