Re: [boost] Case study: Boost.Local versus Boost.Phoenix

Subject: Re: [boost] Case study: Boost.Local versus Boost.Phoenix
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2011-02-04 10:55:05

On 04/02/2011 13:35, Artyom wrote:

> I'm sorry is it only me or it would be much more readable
> and maintainable to write:
>
> namespace {
>     struct my_lambda  {
>         foo_type&foo;
>         bar_type&bar
>         my_lambda(foo_type&local_foo,bar_type&local_bar) :
>             foo(local_foo),
>             bar(local_bar)
>         {
>         }
>
>         void operator()(a_type a) const
>         {
>               /// Your body goes there
>         }
>
>     };
> }
>
> void my_function()
> {
>      foo_type foo;
>      bar_type bar;
>
>      my_lambda lambda(foo,bar);
>      for_each(as.begin(),as.end(),lambda);
>      // or something else
> }

That's exactly the kind of thing Boost.Local does, it generates that 
structure but avoids you the boilerplate of declaring foo and bar 
members and forwarding them in the constructor. Also, it uses 
Boost.Typeof, so you don't have to write their type.

Also, it is much more valuable to declare this as

void my_function()
{
     foo_type foo;
     bar_type bar;

     struct
     {
        foo_type &foo;
        bar_type &bar
        my_lambda(foo_type &local_foo,bar_type &local_bar) :
            foo(local_foo),
            bar(local_bar)
        {
        }

        void operator()(a_type a) const
        {
              /// Your body goes there
        }

     } lambda(foo, bar);
     for_each(as.begin(),as.end(),lambda);
     // or something else
}

since the lambda is right next to where it is used (which is the whole 
point of the exercise).

It is true however that the syntax of the Boost.Local macro could 
greatly be simplified.

I think

LOCAL_FUNCTION(R, f, (a, b, c)(T0 a0, T1 a1), body)

is a better syntax. (a, b, c) would catch a, b, and c in the scope and 
would be optional.

(Of course, it requires the use of the C99 preprocessor)