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Re: Deriving from concrete types like std::list

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Urs Thuermann wrote:
> [...]
>         class StmtList : public Stmt, public std::list <Stmt *> {
>         public:
>                 virtual void exec() {
>                         const_iterator it;
>                         for (it = begin(); it != end(); ++it)
>                                 (*it)->exec();
>                 }
>         };
>
>         // in the parser
>                 stmt_list->push_back(stmt);
>
> Is this, according to Stroustrup, the wrong approach?  Instead of
> deriving I could have a member of type list <Stmt *> in class StmtList
> but iterating would look more cumbersome and I had to implement my own
> push_back() that calls push_back() for that list member, etc.  After
> all, a statement list *is* a list.  Shouldn't I express this
> relationship by derivation?

Oh, my. There are two arguments against this.

First, the nice one: by deriving from std::list you make the interface
of StmtList extremly large. This gives users of StmtList a lot of ways
to mess with its content. Which means that you cannot deduce the behav-
iour of the class from its methods alone. You always have to check that
nobody out there does nothing stupid with its instances. This totally
defeats the reason we are doing OOP.

The second argument is not so nice: your code does not actually work.
That is, your claim that »a statement list *is* a list« is false.
Hint: how many methods of std::list are declared virtual?

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Deriving from concrete types like std::list Urs Thuermann <urs@isnogud.escape.de> - 2011-07-07 14:02 +0200
  Re: Deriving from concrete types like std::list Leigh Johnston <leigh@i42.co.uk> - 2011-07-07 14:04 +0100
  Re: Deriving from concrete types like std::list Alexander Bartolich <alexander.bartolich@gmx.at> - 2011-07-07 13:42 +0000
    Re: Deriving from concrete types like std::list Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-07 22:23 +0200
      Re: Deriving from concrete types like std::list Alexander Bartolich <alexander.bartolich@gmx.at> - 2011-07-07 22:04 +0000
        Re: Deriving from concrete types like std::list Kai-Uwe Bux <jkherciueh@gmx.net> - 2011-07-08 01:16 +0200
    Re: Deriving from concrete types like std::list red floyd <redfloyd@gmail.com> - 2011-07-08 11:23 -0700
      Re: Deriving from concrete types like std::list "Balog Pal" <pasa@lib.hu> - 2011-07-08 20:30 +0200
        Re: Deriving from concrete types like std::list "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-08 21:16 +0200
        Re: Deriving from concrete types like std::list red floyd <redfloyd@gmail.com> - 2011-07-08 14:53 -0700
          Re: Deriving from concrete types like std::list "Balog Pal" <pasa@lib.hu> - 2011-07-09 10:33 +0200
            Re: Deriving from concrete types like std::list Leigh Johnston <leigh@i42.co.uk> - 2011-07-09 10:59 +0100
  Re: Deriving from concrete types like std::list "Bo Persson" <bop@gmb.dk> - 2011-07-07 19:12 +0200
  Re: Deriving from concrete types like std::list "MikeP" <mp011011@some.org> - 2011-07-07 15:51 -0500

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