Idiomatic way to prevent slicing?

Question

Sometimes it can be an annoyance that c++ defaults to allow slicing. For example

struct foo { int a; };
struct bar : foo { int b; };

int main() {
    bar x{1,2         


        

Answer 1

You can prevent the base from being copied outside of member functions of derived classes and the base itself by declaring the copy constructor protected:

struct foo {
    // ...
protected:
    foo(foo&) = default;
};