From: Robert Klemme <bob.news@...>
Date: 2004-12-09T22:22:31+09:00
Subject: Re: Inheritance, mixins and initializers


"Johan Nilsson" <johan.nilsson@---.esrange.ssc.se> schrieb im Newsbeitrag
news:1102597896.fbf426538d0cb3bf826331d7f2d41e34@teranews...
>
> "Robert Klemme" <bob.news@gmx.net> wrote in message
> news:31qukrF3d6rb9U1@individual.net...
> >
> > "Johan Nilsson" <johan.nilsson@---.esrange.ssc.se> schrieb im
Newsbeitrag
> > news:1102594375.344eddcc1c357ac539046c764cd8c6b8@teranews...
> > > Hi,
> > >
> > > I've got a question regarding inheritance, mixins, order of
> > initialization
> > > and calling module/super class "initializers". I'd like to do
something
> > > along the lines of (pseudo-ruby code):
> > >
> [snip]
>
> >
> > I don't know which real problem you are trying to solve.  I can think
of
> > several other approaches.  You might want to store your mixin created
> > instances directly in instance variables and record only the names of
> > these.
>
> Thanks for your reply(s), I'll check them out.
>
> I'm actually mapping a legacy C++ construct to Ruby (no, this is not the
> actual code and probably contain some typos):
>
> ---
> struct FooBarBase {};
> struct Foo : FooBarBase {};
> struct Bar : FooBarBase {};
>
> class Base
> {
> protected:
>     Base(int stuffs)
>         : m_stuff(stuffs, boost::shared_ptr<FooBarBase>())
>     {}
>     void add_stuff_at(int index, boost::shared_ptr<FooBarBase> pfb)
>     {  m_stuff.at(index) = pfb; }
>
> public:
>     ... functions operating on all "stuff" as a homogenous collection
....
> private:
>     std::vector<boost::shared_ptr<FooBarBase> > m_stuff;
> };
>
> template<typename Mixee, int which>
> struct FooMixin
> {
>     FooMixin()
>         :  m_pFoo(boost::shared_ptr<Foo>(new Foo))
>     { return static_cast<Mixee*>(this)->add_stuff_at(which, m_pFoo); }
>
>     const Foo& foo() const
>     { return *m_pFoo; }
> private:
>     boost::shared_ptr<Foo> m_pFoo;
> };
>
> template<typename Mixee, int which>
> struct BarMixin
> { ... };
>
> struct Derived
>     : Base
>     , FooMixin<Derived, 0>
>     , BarMixin<Derived, 1>
> {
>     Derived()
>       : Base(2)
>     {}
> };
>
> int main(int, char*[])
> {
>     Derived d;
>     const Foo& foo = d.foo();
>     d.bar();
>     return 0;
> }
>
> ---
>
> To further complicate matters I was trying to use SWIG to inherit from
the
> C++ class "Base" using the cross-language polymorhism feature. Now I
believe
> I'll rewrite this part in Ruby instead (but the FooBaseBase stuff etc
will
> still be wrapped from C++).

This sounds awfully complicated.  Good luck!

> Thanks again

You're welcome!

Kind regards

    robert