Re: [Boost-users] [parameter] Return type dependent on parameter type?

From: David Abrahams (dave_at_[hidden])
Date: 2007-10-01 17:30:21

on Sun Sep 30 2007, François Duranleau <duranlef-AT-iro.umontreal.ca> wrote:

> Hi!
>
> I have a function like this:
>
> template< typename Arg0 ,
>            typename Arg1 ,
>            ... >
> Arg1 the_function( Arg0 arg0 , Arg1 arg1 , ... ) { ... }
>
> The return type should be the same as one of its parameters, and all '...' 
> are optional parameters. Is there a way to use BOOST_PARAMETER_FUNCTION in 
> such a case? I didn't find anything in the documentation about it. I tried 
> this:
>
> BOOST_PARAMETER_NAME( (arg1 , kw) arg1 )
> BOOST_PARAMETER_NAME( (arg2 , kw) arg2 )
>
> BOOST_FUNCTION_PARAMETER(
>      (kw::arg2::_) ,
>      the_function ,
>      kw ,
>      (required (arg1 , *) (arg2 , *))
>      (optional ...)
> )
>

Try:

  BOOST_PARAMETER_NAME( (arg1 , kw) arg1 )
  BOOST_PARAMETER_NAME( (arg2 , kw) arg2 )

  BOOST_PARAMETER_FUNCTION(
       (arg1_type) ,
       the_function ,
       kw ,
       (required (arg1 , *) (arg2 , *))
       (optional ...)
  )
  {
      return arg1;
  }

See
http://boost.org/libs/parameter/doc/html/index.html#adding-type-requirements

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com