Re: [Boost-users] boost::any Question

From: Christian Henning (chhenning_at_[hidden])
Date: 2005-10-10 08:58:32

Just some short questions. Are you sure you want save all the kinds of
types that are available on this planet? Or do want to save a subset
that is a countable?

On 10/9/05, Piyush Kapadia <piyush.kapadia_at_[hidden]> wrote:
> Let's say if using -
> std::map<string, boost::any> tmap;
>
> Now you can put anything in tmap, which could be primitive types or vector
> or another map.
>
> Then you want to implement
>
> ostream& operator << (ostream& os, const tmap& _map)
> {
>         // Over here we need to identify -
>         // if iterator->second is primitive type, vector, map or unknown
> type.
>         // Depending up on that we can decide if we need to iterate through
>         // another vector or simply use << for primitive type.
>         // That's why is_primitive or other type_traits functions may help.
>
>         // Ideally we need switch statement like following
>         switch(type(_map)) {
>                 case int :
>                 case double :
>                 case long :
>                         return os<< _map;
>                 case vector :
>                 {// interate through vector here. }
>                 ..
>                 .. // and so on.
>
>         }
>
> }
>
> -----Original Message-----
> From: boost-users-bounces_at_[hidden]
> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Christian Henning
> Sent: Saturday, October 08, 2005 6:10 PM
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] boost::any Question
>
> I'm not sure why you would want to use traits here. I think traits are
> used for compile-time if...else tests on types.
>
> Why not use a static numerical member in classes that you put in your
> map and so you could use a switch statement to figure out what type
> you are using?
>
> There are probably better ways to do that. RTTI ain't!
>
> Christian
>
>
>
> On 10/7/05, Piyush Kapadia <piyush.kapadia_at_[hidden]> wrote:
> >
> >
> >
> > I am new user of Boost, I tried to use boost::variant first, but in
> > comparison to boost::any performance of boost::variant appears to be
> around
> > 4 times slower, so settled for boost::any.
> >
> >
> >
> > Also boost::any has cleaner interface but I don't know how to query
> current
> > type information for boost::any ?
> >
> >
> >
> > My code looks like following
> >
> >
> >
> > map<unsigned int, boost::any> result_table;
> >
> >
> >
> > result_table[1] = 543.434;
> >
> > vector<int> vec;
> >
> > .. Some vec population code;
> >
> > result_table[2] = vec;
> >
> >
> >
> > Now I need to develop a stringify function for result_table;
> >
> >
> >
> > I can fetch the results back as
> >
> > boost::any value = result_table[2];
> >
> >
> >
> > But I need to know the type of value, so that I can treat it accordingly
> to
> > stringify;
> >
> > I know there exists type_traits, but very limited examples of type_traits
> is
> > provided on Boost documentation and particularly, I am clueless about how
> to
> > use type_traits in above context to find out what is the current type
> > returned by result_table[int]
> >
> >
> >
> > Also I want to know if Boost has any Hash map implementation that can be
> > superior in performance compare to regular std::map ??
> >
> >
> >
> > Thanks,
> >
> >
> >
> >
> >
> > Piyush
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> > http://lists.boost.org/mailman/listinfo.cgi/boost-users
> >
> >
>
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