privatising public member functions in derived classes.

[Firkraag]

Hello

#include <iostream>
using std::cout;

struct A {
~virtual A(){}
virtual void foo(){ cout << "aaa\n"; }
};

struct B : A {
private:
virtual void foo(){ cout << "bbb\n"; }
};

void bar(A& ab)
{
ab.foo();
}
int main()
{
A a;
B b;
bar(b)
}

The above code works properly. As far as I know LSP is not being
violated here. So why FAQ lite says this:
http://www.parashift.com/c++-faq-lit....html#faq-21.1

[Victor Bazarov]

Firkraag wrote:

#include <iostream>
using std::cout;

struct A {
~virtual A(){}
virtual void foo(){ cout << "aaa\n"; }
};

struct B : A {
private:
virtual void foo(){ cout << "bbb\n"; }
};

void bar(A& ab)
{
ab.foo();
}
int main()
{
A a;
B b;
bar(b)
}

The above code works properly. As far as I know LSP is not being
violated here. So why FAQ lite says this:
http://www.parashift.com/c++-faq-lit....html#faq-21.1

Compile this version of 'main' instead:

template<class Tvoid callFoo(T &t)
{
t.foo();
}

int main()
{
B b;
callFoo(b);
}

Now, the "duck typing" doesn't work, does it? LSP or not, what is
the point of hiding 'foo' in 'B'? If you didn't intend to call the
'foo' member directly, you ought to make it private and keep it
private:

struct A {
private:
virtual void foo() { cout << "aaa\n"; }
public:
void doFoo() { foo(); }
};

struct B : A {
private:
virtual void foo() { cout << "bbb\n"; }
};

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Ron Natalie]

Firkraag wrote:

}

The above code works properly. As far as I know LSP is not being
violated here. So why FAQ lite says this:
http://www.parashift.com/c++-faq-lit....html#faq-21.1

First the name is looked up.
Then overloads for the found name are considered.
Then the access for the best overload is considered.

THEN, if the function is virtual, the final overrider is
invoked.
As with most everything else in C++, the thing that matters
is the static declaration at the pointer of the call.