query-resolver.cpp

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/*
  QueryResolver  -  interface for discovering contents of a scope
 
   Copyright (C)
     2009,            Hermann Vosseler <Ichthyostega@web.de>
 
 **Lumiera** is free software; you can redistribute it and/or modify it
 under the terms of the GNU General Public License as published by the
 Free Software Foundation; either version 2 of the License, or (at your
 option) any later version. See the file COPYING for further details.
 
* *****************************************************************/
 
 
#include "lib/multifact.hpp"
#include "common/query/query-resolver.hpp"
 
namespace lumiera {
  
  
  
  /* generate vtables here... */
  
  Goal::~Goal() { }
  
  Resolution::~Resolution() { }
  
  QueryResolver::~QueryResolver() { }
  
  
  
  typedef Goal::QueryID const& QID;
  
  
  
  
  
  
  /* == dispatch to resolve typed queries == */
  
  using lib::factory::BuildRefcountPtr;
  using lib::factory::MultiFact;
  
  
  typedef MultiFact< Resolution*(Goal const&) // raw signature of fabrication
                   , Goal::QueryID           //  select resolution function by kind-of-Query
                   , BuildRefcountPtr       //   wrapper: manage result set by smart-ptr
                   > DispatcherTable;      //
  
  class QueryDispatcher
    : public DispatcherTable
    {
    public:
      
      PReso
      handle (Goal const& query)
        {
          QID qID = query.getQID();
          ENSURE (contains (qID));
          
          return this->invokeFactory (qID, query);
        }                    // qID picks the resolution function
    };
  
  
  
  QueryResolver::QueryResolver ()
    : dispatcher_(new QueryDispatcher)
    { }
  
  
  PReso
  QueryResolver::issue (Goal const& query)  const
  {
    REQUIRE (!dispatcher_->empty(), "attempt to issue a query without having installed any resolver (yet)");
    
    if (!canHandle (query))
      throw lumiera::error::Invalid ("unable to resolve this kind of query"); 
    
    return dispatcher_->handle(query);
  }
  
  
  void
  QueryResolver::installResolutionCase (QID qID, ResolutionMechanism resolutionFun)
  {
    ENSURE (!dispatcher_->contains (qID),
            "duplicate registration of query resolution function");
    
    dispatcher_->defineProduction (qID, resolutionFun);
  }
  
  
  
  
} // namespace lumiera