From: Rene Rivera (grafik.list_at_[hidden])
Date: 2004-11-16 02:45:03
E. Gladyshev wrote:
> 1. I think that one of the important
> applications of the library is creating
> named parameters wrapper around legacy
> C interfaces with a bunch of parameters.
> It seems to me that named parameters functors
> are an elegant way to do it without macros.
> I personally belong to a large group
> of developers who don't favor macros unless there are
> really necessary. Please I don't mean to
> get into a discussion about macros in general.
I don't remember there being a requirement to use macros on this
named_params library. And I showed how to do exactly that, wrap C style
function, in my example (in my review) without macros.
> Here is an example with class members.
> I think that it is much more fun
> than macros. :)
>
> struct widget
> {
> //define a named parameters functor
> typedef ttl::func::named_params_function<
> int //the function returns 'int'
> (
> //'argument name', 'argument type'
> title, const char*
> , style, ttl::func::numeric_argument<int, 45>
> //the default is 45
> )
> > create_functor;
>
> //
> widget()
> {
> //initialize the functor with create_impl
> create = boost::bind( &widget::create_impl, this, _1, _2 );
> }
>
> create_functor create;
>
> private:
> int create_impl( const char* title, int style );
> };
>
> main()
> {
> widget w;
>
> w.create( w.create.arg<title>("my widget") );
>
> return 0;
>
> }
It may be "fun", but the overhead is overwhelming. I find this
alternative more appealing...
namespace {
boost::keyword<struct title_t> title;
boost::keyword<struct style_t> style;
}
struct widget {
widget() { }
int create( const char * title, int style );
template<class Params>
inline int create(const Params & params) {
return create(params[title], params[style | int(45));
}
};
int main() {
widget w;
w.create((title = "my widget));
return 0;
}
Especially considering that the overhead is *zero* with release
optimizations. And you can also do the more normal construction by adding:
template<class Params>
widget(const Params& params) {
create(params[title], params[style | int(45));
}
I fail to see how the functor gives you anything here. Perhaps you need
a better counter example?
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