Re: privatising public member functions in derived classes.
werasm wrote:
On Nov 21, 5:12 am, "Victor Bazarov" <v.Abaza...@comAcast.net> wrote:
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"; }
};
To me this also seems a little pointless. If I want to convey
to clientA that he may only call foo (or doFoo, for that
matter), nothing stops client B from calling doFoo().
But that's the whole point! The client of A or B or any other
derived classes will have to always call doFoo() instead of
'foo' (which can have different behaviour due to static or
dynamic binding, IOW when calling through a pointer or directly
for an object).
What you are showing here above allows doFoo to dictate
the order of the calling (template method)
What template method? What are you talking about?
if there is
an order, but it does not help with indicating which
client is supposed to use the applicable interface.
Huh?
This however does:
Does what, exactly?
class A
{
friend class ClientOfA;
virtual void foo() = 0;
//...
};
or...
class A
{
friend class ClientOfA;
void doFoo(){ /*..call foo etc...*/ }
virtual void foo() = 0;
};
class B{}; //All above private.
The idiom of having all virtual interface private (pure or not)
and having a public interface that just forwards the calls to the
virtual function, is well known and commonly accepted in the
industry. The main advantage is that there is a single point of
call for all classes in the hierarchy, where you can put your
pre- and post-conditions, and the virtual interface is never
exposed for an occasional non-virtual call (where you can't tell
just by looking which of the functions is going to be called).
V
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