Re: deriving a class with a subset of base class methods?
AK wrote:
Is there a C++ approach to deriving a class such that only a subset of
the base class' public member functions are available to it?
Yes, refactor your design so that this is not necessary. The typical example
where things like you request are done is in some widget sets where the
baseclass contains all functions possible and the derived classes implement
those that make sense to them and leave the others as stubs.
For a concrete example: I may wish to use STL's linked list class to
create a new "specialized" linked list class in which nodes can only
be added to the list according to some specified ordering rule (say
defined by '<', appropriately defined for the node type), so I don't
want to provide the user of my specialized linked list to be able to
use the push_back() and push_front() methods from STL's linked list.
Do I need to override these functions so that they don't do anything
in my derived class, or is there a better way?
This is a slightly different thing. What I guess you actually want is a
special container. For that, it is useful to base your work on existing
container types, but that should be an implementation detail. In
particular, you should not derive your container publicly from std::list,
but rather derive privately or use aggregation. In any case, if the user
gets hold of the std::list part of your class, they can also use push_front
on it, you can not change that. What you can change is access to the
std::list, i.e. you wrap it in your code. In that case, private derivation
comes handy, because for the 'safe' parts you can then simply forward them
with 'using baseclass::begin;' because this function can't change the
required order.
In any way, the OOP approach using derivation is not applicable, because
std::list has no virtual functions that you could customise. Rather, you
will have to use containment, private derivation being just a C++-specific
way of containment.
Uli
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