Re: [Boost-users] [spirit][karma+phoenix] Show result of member function

Subject: Re: [Boost-users] [spirit][karma+phoenix] Show result of member function
From: Ravi (lists_ravi_at_[hidden])
Date: 2010-04-06 20:41:25

On Tuesday 06 April 2010 08:52:42 Hartmut Kaiser wrote:
> > How can karma be used to show the result of applying a member function to
> > objects in a container? Consider the following code (which does not 
compile)
> > to show the real and the imaginary parts of complex numbers stored in a 
vector:
>  
> I added a new example (libs/spirit/example/karma/complex_number_adapt.cpp)
> demonstrating how to solve this by employing the new FUSION_ADAPT_CLASS
> macro.

Thank you for the example. While this examples solves the specific problem of 
displaying complex numbers, it does not address my original question: how can 
phoenix be used with karma to assign the result of a member function to the 
attribute of a generator? For example, some complicated classes might have 20 
member functions, each of which might be used with some specific grammar; in 
this case, the approach of using FUSION_ADAPT_CLASS would obscure the clarity 
of the grammar with a lot of "omit" directives.

On other words, how would I replace the following so that it works for the 
complex number class?
  double_[ _1 = phoenix::bind( member_func, _val ) ]
My understanding (and, apparently, OvermindDL1's as well) of phoenix and karma 
leads me to believe that the preceding should work.

On a related note, the qi tutorial example for parsing into a struct does not 
show the simplest and, IMHO, the most maintainable way to fill up a struct 
that may evolve over time or simply has a lot of elements (such as a very 
application-specific config file parser):
  int_[ phoenix::bind( &employee::age, _val ) = _1 ] >>
  quoted_string[ phoenix::bind( &employee::forename, _val ) = _1 ]
While the preceding may be inefficient due to use of semantic actions, it 
generalizes much better since it is essentially self-documenting (compared to 
at_c). FUSION_ADAPT_STRUCT is nice, but nowhere near as intuitive as above - 
all in my humble opinion, of course.

Regards,
Ravi