Re: [Boost-users] [spirit] closures and actions

From: Hubert Hoover (hugh_at_[hidden])
Date: 2007-01-04 14:08:23

For the record - I figured out my problem, which was a bit
of confusion about what was an actor and how to access closure members.
The "ref" passed in is a phoenix::actor, NOT the closure member itself,
so to access the closure member, the operator()() of the actor needs
to be invoked - substituting into the do_appender::act below:

String& value(ref());
value += val;

Of course, if act is called with something other than an actor, THIS  
will
break, but I'm thinking it should ONLY be fed actors...  And for my  
purposes,
only an actor that returns a std::string&.

On Jan 2, 2007, at 17:09, Hugh Hoover wrote:

> I'm trying to build a parser that does a fairly simple  
> transformation of an input string - kind of like an L-System.
> I can get rules to properly match the input string, but I'm having  
> real trouble with DOING anything.  For testing,
> I've created some simple actions and a grammar (and rules) with a  
> closure.  When I don't use the closure for
> "temporary" variables, I seem to be able to proceed, but when I do  
> anything except assign a value to my closure
> result, I'm getting failures to compile.  This is using gcc4.01 on  
> MacOSX and spirit 1.8.3 (from boost 1.34).
>
> The specific compiler error is:
> ../../src/lsystem/catalog_lsystem.cpp: In member function 'void  
> do_appender::act(T&, const IteratorT&, const IteratorT&) const  
> [with T = phoenix::actor<phoenix::closure_member<0,  
> phoenix::closure<String, size_t, String> > >, IteratorT =  
> __gnu_cxx::__normal_iterator<char*, std::basic_string<char,  
> std::char_traits<char>, std::allocator<char> > >]':
> <snip>
> ../../src/lsystem/catalog_lsystem.cpp:211: error: no matching  
> function for call to 'std::basic_string<char,  
> std::char_traits<char>, std::allocator<char> >::basic_string 
> (phoenix::actor<phoenix::closure_member<0, phoenix::closure<String,  
> size_t, String> > >&)'
>
> From the error, it appears that I need some transformation from  
> phoenix::actor
> back into my closure member, which is a String (typedef for  
> std::basic_string<char>).
>
> Any suggestions?
>
> do_appender (a simple example actor) looks like:
>
>     struct do_appender {
>         template <typename T, typename ValueT>
>         void act(T& ref, ValueT const &val) const
>         {
>             ref += val;
>         }
>
>         template <typename T, typename IteratorT>
>         void act(T& ref, IteratorT const &first, IteratorT const &  
> last) const
>         {
>             String s(first, last);
>             ref += s;
>         }
>     };
>