C++: rationale behind hiding rule

Question

What\'s the rationale behind the hiding rule in C++?

class A { void f(int); }
class B : public A { void f(double); } // B::f(int) is hidden

Answer 1

Another reason for hiding base class's member function (with same name but different signatures) might be due to ambiguity caused by optional parameters. Consider the following example:

#include 

class A
{
public:
    int foo(int a, int b=0)
    {
        printf("in A : %d, %d\n", a, b);
    }
};

class B : public A
{
public:
    int foo(int a)
    {
        printf("in B : %d\n", a);
        foo(a); //B:foo(a) will be called unless we explicitly call A:foo(a)
        foo(a, 1); // compile error: no matching function for call to B:foo(int&, int)
    }
};


int main()
{
    B b;
    b.foo(10);
    return 0;
}

If the foo method in base class hadn't become hidden, it wouldn't be possible for compiler to decide whether A::foo should be called or B::foo since the following line matches both signatures:

foo(a);