Re: [boost] [Property Map] Composition of properties

From: Cromwell Enage (sponage_at_[hidden])
Date: 2006-09-15 19:38:47

--- Benoit wrote:
> Hello everyone,

Howdy!

> I have been using properties quite extensively in
> my work.  And these last days I have needed to
> combine properties numerous times.
> 
> By that, I mean that I have n properties p1, p2, ...
> pn and what I use is
>       get( p1, get( p2, get( ..., get( pn, object ) 
> ... ) ) )
> I would very much want to make a composite property
> p to be used like this :
>       get( p, object )
> (most of the time, n=2, but why stop there ? :-) )
> 
> I have to tried to find such functionality but in
> vain so far... Does it not exist?  Are there
> obstacles that i have not foreseen?  I am
> thinking of something like the following:
> 
>     template<class Prop1, class Prop2>
>     struct composite_property
>     {
>         composite_property(Prop1 p1_, Prop2 p2_)
>           : p1( p1_ ), p2( p2_ )
>         {
>         }
> 
>         Prop1 p1;
>         Prop2 p2;
>     };
> 
>     template<class Prop1, class Prop2>
>     typename property_traits<Prop1>::reference
>         get(composite_property<Prop1, Prop2> comp,
>         typename property_traits<Prop2>::reference
x)
>     {
>         return get( comp.p1, get( comp.p2, x ) );
>     }
> 
> How do you all feel about this?  I believe it would
> be very useful!

I believe that the Fusion library provides a map that
possesses the functionality you need.  You can wait
until Boost version 1.34 is released, or you can grab
a CVS snapshot in order to play with it right away.

                              HTH,
                              Cromwell D. Enage

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com