Re: [boost] [local] Any "active Boost library author" in favor of Boost.Local?

Subject: Re: [boost] [local] Any "active Boost library author" in favor of Boost.Local?
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2011-11-25 15:09:48

Le 25/11/11 20:21, Mathias Gaunard a écrit :
> On 11/25/2011 05:06 PM, Vicente Botet wrote:
>
>> That means that the interface of the local function is equivalent to 
>> the one
>> we could write directly using a global function (I think that just don't
>> needing to repeat the types is not a major advantage).
>
> Of course it's equivalent, it's a macro.
>
> The point is that
>
> struct f_
> {
>    T0& a;
>    T1& b;
>    T2& c;
>    T3& d;
>
>    f_(TO& a_, T1& b_, T2& c_, T3& d_)
>     : a(a_), b(b_), c(c_), d(d_)
>    {
>    }
>
>    R operator()(A0 const& arg0, A1 const& arg1) const
>    {
>        return arg1 * a + arg2 / b + sin(c) * cos(d);
>    }
> };
>
> f_ f(a, b, c, d);
>
> Is quite more verbose to write than
>
> R BOOST_LOCAL_FUNCTION_PARAMS( bind a, bind b, bind c, bind d
>                              , A0 const& arg0, A1 const& arg1
>                              )
> {
>     return arg1 * a + arg2 / b + sin(c) * cos(d);
> }
> BOOST_LOCAL_FUNCTION_NAME(f)
>

I was comparing it to

    R f(TO& a, T1& b, T2& c, T3& d, A0 const& arg0, A1 const& arg1)
    {
        return arg1 * a + arg2 / b + sin(c) * cos(d);
    }
    //...
    R r = f(a,b,c,d,a0,a1);
> This macro automates the tedious forwarding of the context to a functor.
> It is, to me, its main use.
>
Forwarding the context could be only useful if the function is called 
several times, so the context is passed only once.
> With Phoenix, I would write it as
>
> // these two macros must be at file scope
> BOOST_PHOENIX_ADAPT_FUNCTION(R, sin_, sin, 1)
> BOOST_PHOENIX_ADAPT_FUNCTION(R, cos_, cos, 1)
>
> BOOST_AUTO(f, arg1 * a + arg2 / b + sin_(c) * cos_(d));
>
> The Phoenix version comes with many disadvantages however that have 
> already been covered, and it's not that much better at terseness and 
> macro-less-ness than Boost.Local.
>
I'm not seen this as an alternative to Boost.Local, as the goal is to 
been able to write the action using c++ statements. So the comparison is 
not fair.
> I think it is apparent however that the BOOST_LOCAL_* macros are quite 
> practical in comparison to the manually-written functor at the top.

I don't know if you have seen the example provided by Joel. If not 
please take a look.

Best,
Vicente