Re: [Boost-Users] Re: (Spirit) Semantic Actions with member functions?

From: Joel de Guzman (djowel_at_[hidden])
Date: 2003-05-11 21:17:51

Rainer Deyke wrote:
> Slava Akhmechet wrote:
>> I was able to get boost::bind working to bind the semantic action to
>> the member function of MyGrammar. This seems like a superior
>> solution. In any case, I am not sure how to pass custom data to a
>> functor. When specifing a semantic action I have to pass the type of
>> the functor, which implies that spirit creates a temporary object. Am
>> I missing something?
> 
> No, you pass an instance of the functor, which can be cosntructed with
> arbitrary arguments.
> 
> struct functor {
>   f(char const *s) : msg(s) {}
>   template<class Iter> void operator(Iter, Iter)
>   {
>     std::cout << this->msg;
>   }
>   char const *msg;
> };
> 
> parse(something, something_p[functor("something")]);

The preferred way is to keep the semantic functors as light as possible.
As Rainer suggested, a pointer is ok. As for me, I prefer keeping a
reference to some external data. Example:

struct functor {
   f(T& data) : data(data) {}
   template<class Iter> void operator(Iter, Iter);  
   T& data;
};

BTW, I suggest continuing this thread here:

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-- 
Joel de Guzman
joel at boost-consulting.com
http://www.boost-consulting.com
http://spirit.sf.net