JBaseClass.hh

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#ifndef __JLANG__JBASECLASS__
#define __JLANG__JBASECLASS__
 
#include "JLang/JConversion.hh"
#include "JLang/JTypeList.hh"
 
/**
 * \file
 *
 * Auxiliary class to identify common base class in type list.
 * \author mdejong
 */
namespace JLANG {}
namespace JPP { using namespace JLANG; }
 
namespace JLANG {
 
  /**
   * Template class to test for polymorphism.
   */
  template<class JBase_t, class JDerived_t>
  struct JBaseType_t {
    static const bool is_base = (JConversion<JDerived_t, JBase_t>::is_derived); //!< true if JBase_t is a base class of JDerived_t; else false
  };
  
 
  /**
   * Template class to test for polymorphism.
   *
   * The class recursively tests whether both 
   *  - JBaseType<JBase_t, JHead_t>::is_base; and
   *  - JBaseType<JBase_t, JTail_t>::is_base
   * evaluate to true.
   */
  template<class JBase_t, class JHead_t, class JTail_t>
  struct JBaseType_t< JBase_t, JTypeList<JHead_t, JTail_t> >
  {
    static const bool is_base = (JBaseType_t<JBase_t, JHead_t>::is_base &&
                                 JBaseType_t<JBase_t, JTail_t>::is_base);
  };
 
  
  /**
   * Terminator class of recursive JBaseType_t class.
   */
  template<class JBase_t, class JHead_t>
  struct JBaseType_t< JBase_t, JTypeList<JHead_t, JNullType> >
  {
    static const bool is_base = (JBaseType_t<JBase_t, JHead_t>::is_base);
  };
 
  
  /**
   * Template class to identify common base class.
   *
   * The parameter data_type corresponds to the common base class.
   */
  template<class JBase_t,         // assumed base class
           class JHead_t,         // upstream   type list
           class JTail_t,         // downstream type list
           bool is_base = (JBaseType_t<JBase_t, JHead_t>::is_base &&
                           JBaseType_t<JBase_t, JTail_t>::is_base) >
  struct JBaseType
  {
    typedef JBase_t           data_type;
  };
 
  
  /**
   * Resursive scan for base class.
   */
  template<class JBase_t,         // assumed base class
           class JTypelist_t,     // upstream   type list
           class JHead_t,         // upstream   data type of downstream type list
           class JTail_t>         // downstream data type of downstream type list
  struct JBaseType<JBase_t, JTypelist_t, JTypeList<JHead_t, JTail_t>, false> 
  {
    typedef typename JBaseType<JHead_t, JTypeList<JTypelist_t, JHead_t>, JTail_t>::data_type  data_type;
  };
 
  
  /**
   * Terminination class of resursive JBaseType class.
   */
  template<class JBase_t,         // assumed base class
           class JTypelist_t,     // upstream   type list
           class JHead_t>         // upstream   data type of downstream type list
  struct JBaseType<JBase_t, JTypelist_t, JTypeList<JHead_t, JNullType>, false> 
  {
    typedef typename JBaseType<JHead_t, JTypelist_t, JHead_t>::data_type  data_type;
  };
  
 
  /**
   * Template definition of class to look for base class in type list.
   *
   * The type of the base class is defined as data_type.
   */
  template<class T>
  struct JBaseClass {
    typedef T  data_type;
  };
 
 
  /**
   * Template specialisation of class to look for base class in type list.
   */
  template<class JHead_t, class JTail_t>
  struct JBaseClass< JTypeList<JHead_t, JTail_t> >
  {
    typedef typename JBaseType<JHead_t, JHead_t, JTail_t>::data_type  data_type;
  };
}
 
#endif