Re: [boost] programmatically building a bind composition?

From: Arkadiy Vertleyb (vertleyb_at_[hidden])
Date: 2006-11-03 11:41:29

"Fernando Cacciola" <fernando_cacciola_at_[hidden]> wrote

> Say I have a few arbitraty function objects:
>
> A a ; B b ; C c ;
>
> I can easily pipe them toghether using Boost.Bind:
>
> bind(a, bind(b, bind(c,_1) ) )(some_starting_value);
>
> But how do I create such a composed functor programatically from an 
> aribtrary tuple of function objects, as in tuple<A,B,C>?
>
> The idea is to present to the user a simple interface were he pass just a 
> tuple of functors and I do the magic of turning them into a pipe.

I think you may need Fusion to do this...  The pseudocode would be roughly 
something like:

unspecified compose(Tuple t, F f)
{
    return compose(tail(t), bind(head(t), f)),
}

F compose(EmptyTuple, F f)
{
    return f;
}

compose(tuple(a, b, c), _1)

(except I think the order may be inverted)

But I don't think current boost::tuple allows for extracting head and tail. 
Fusion may also have some kind of "fold" algorithm to do this, but I am not 
sure.

Also, if you can't use typeof, you would have to get into bind's 
implementation details to calculate the return type.

FWIW.

Regards,
Arkadiy