Re: [Boost-users] Metaprogramming Question

Subject: Re: [Boost-users] Metaprogramming Question
From: Nat Linden (nat_at_[hidden])
Date: 2012-02-09 14:49:15

On Thu, Feb 9, 2012 at 1:13 AM, John M. Dlugosz <mpbecey7gu_at_[hidden]>wrote:

I've not had much opportunity to do much template metaprogramming in my
> work, but I've kept up with my reading.  So, might I get some advice on how
> to approach this problem?
>
> I'm thinking of an assert-like statement that follows the syntax of
> Boost.Format, thus avoiding the variadic argument list.
>
> But, I want to avoid doing any work except on failure.  This means
> remembering the arguments including the following %arg stuff, and passing
> everything through to Boost.Format based on the condition.
>

This isn't metaprogramming -- or at least not new metaprogramming, rather
taking advantage of an existing library -- but my colleague came up with
what I consider a clever use of Boost.Lambda for a similar sort of problem.
We wanted a macro with usage of the form:

OURMACRO("some streaming expr " << value << ...);

that would stream arbitrary objects as in:

hidden_ostream_object << "some streaming expr " << value << ...;

His solution is like this:

template <typename FUNCTOR>
void ourmacro_f(const FUNCTOR& f)
{
    f(hidden_ostream_object);
}

#define OURMACRO(EXPRESSION) (ourmacro_f(boost::lambda::_1 << EXPRESSION))

> So, what approach should I use?
>    Plain MPL and classic metaprogramming?
>    Fusion?
>    Phoenix?
>

In this case I guess Phoenix would be the way to go rather than
Boost.Lambda.