LUMIERA.clone/src/tool/try.cpp

/* try.cpp  -  for trying out some language features....
 *             scons will create the binary bin/try
 *
 */ 

// 8/07  - how to control NOBUG??
//         execute with   NOBUG_LOG='ttt:TRACE' bin/try
// 1/08  - working out a static initialisation problem for Visitor (Tag creation)
// 1/08  - check 64bit longs
// 4/08  - comparison operators on shared_ptr<Asset>
// 4/08  - conversions on the value_type used for boost::any
// 5/08  - how to guard a downcasting access, so it is compiled in only if the involved types are convertible


#include <nobug.h>
#include <iostream>
#include <typeinfo>

#include <boost/type_traits/is_convertible.hpp>
#include <boost/type_traits/is_polymorphic.hpp>
#include <boost/type_traits/is_base_of.hpp>
#include <boost/type_traits/remove_pointer.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <boost/utility/enable_if.hpp>


using std::string;
using std::cout;
using std::ostream;


    using boost::remove_pointer;
    using boost::remove_reference;
    using boost::is_convertible;
    using boost::is_polymorphic;
    using boost::is_base_of;
    using boost::enable_if;
    
    template <typename SRC, typename TAR>
    struct can_cast : boost::false_type {};

    template <typename SRC, typename TAR>
    struct can_cast<SRC*,TAR*>          { enum { value = is_base_of<SRC,TAR>::value };};

    template <typename SRC, typename TAR>
    struct can_cast<SRC*&,TAR*>         { enum { value = is_base_of<SRC,TAR>::value };};

    template <typename SRC, typename TAR>
    struct can_cast<SRC&,TAR&>          { enum { value = is_base_of<SRC,TAR>::value };};
    
    
    template <typename T>
    struct has_RTTI
      {
        typedef typename remove_pointer<
                typename remove_reference<T>::type>::type TPlain;
      
        enum { value = is_polymorphic<TPlain>::value };
      };
    
    template <typename SRC, typename TAR>
    struct use_dynamic_downcast
      {
        enum { value = can_cast<SRC,TAR>::value
                       &&  has_RTTI<SRC>::value
                       &&  has_RTTI<TAR>::value
             };
      };
    
    template <typename SRC, typename TAR>
    struct use_static_downcast
      {
        enum { value = can_cast<SRC,TAR>::value
                    && (  !has_RTTI<SRC>::value
                       || !has_RTTI<TAR>::value
                       )
             };
      };
    
    template <typename SRC, typename TAR>
    struct use_conversion
      {
        enum { value = is_convertible<SRC,TAR>::value
                    && !( use_static_downcast<SRC,TAR>::value
                        ||use_dynamic_downcast<SRC,TAR>::value
                        )
             };
      };
    

    template<typename X>
    struct EmptyVal
      {
        static X create() 
          {
            cout << " NULL() " << __PRETTY_FUNCTION__ <<"\n";
            return X(); 
          }
      };
    template<typename X>
    struct EmptyVal<X*&>
      {
        static X*& create() 
          {
            cout << " NULL & " << __PRETTY_FUNCTION__ <<"\n";
            static X* null(0);
            return null; 
          }
      };
    
    
    template<typename RET>
    struct NullAccessor
      {
        typedef RET Ret;
        
        static RET access  (...) { return ifEmpty(); }
        static RET ifEmpty ()    { return EmptyVal<RET>::create(); }
      };
    
    template<typename TAR>
    struct AccessCasted : NullAccessor<TAR>
      {
        using NullAccessor<TAR>::access;
        
        template<typename ELM>
        static  typename enable_if< use_dynamic_downcast<ELM&,TAR>, TAR>::type
        access (ELM& elem) 
          { 
            cout << " dynamic " << __PRETTY_FUNCTION__ <<"\n";
            return dynamic_cast<TAR> (elem); 
          }
        
        template<typename ELM>
        static  typename enable_if< use_static_downcast<ELM&,TAR>, TAR>::type
        access (ELM& elem) 
          { 
            cout << " static " << __PRETTY_FUNCTION__ <<"\n";
            return static_cast<TAR> (elem); 
          }
        
        template<typename ELM>
        static  typename enable_if< use_conversion<ELM&,TAR>, TAR>::type
        access (ELM& elem) 
          { 
            cout << " convert " << __PRETTY_FUNCTION__ <<"\n";
            return elem; 
          }
            
      };




struct B {};
struct D : B {};

struct E : D
  {
    virtual ~E() {};
  };
struct F : E {};


ostream& operator<< (ostream& s, const B& b) { return s << "B{} adr="<<&b; }
ostream& operator<< (ostream& s, const D& d) { return s << "D{} adr="<<&d; }
ostream& operator<< (ostream& s, const E& e) { return s << "E{} adr="<<&e; }
ostream& operator<< (ostream& s, const F& f) { return s << "F{} adr="<<&f; }

int 
main (int argc, char* argv[])
  {
    
    NOBUG_INIT;
    
    D d;
    D* pD =&d;
    B* pB =pD;
    D& rD = *pD;
    B& rB = *pB;

    D*& rpD = pD;
    B*& rpB = pB;

    F f;
    E& rE = f;
    E* pE = &f;
    D* pDE = pE;
    
    cout <<  "is_base_of<B,D> = "   << is_base_of<B ,D >::value << "\n";
    cout <<  "is_base_of<B*,D*> = " << is_base_of<B*,D*>::value << "\n";
    cout <<  "is_base_of<B&,D&> = " << is_base_of<B&,D&>::value << "\n";

    cout <<  "can_cast<B,D> = " << can_cast<B,D>::value << "\n";
    cout <<  "can_cast<B*,D*> = " << can_cast<B*,D*>::value << "\n";
    cout <<  "can_cast<B&,D&> = " << can_cast<B&,D&>::value << "\n";
    cout <<  "can_cast<B&,D*> = " << can_cast<B&,D*>::value << "\n";
    cout <<  "can_cast<B*,D&> = " << can_cast<B*,D&>::value << "\n";
    cout <<  "can_cast<B*&,D*&> = " << can_cast<B*&,D*&>::value << "\n";
    cout <<  "can_cast<D*&,D*&> = " << can_cast<D*&,D*&>::value << "\n";

    cout <<  "can_cast<D*,E*> = " << can_cast<D*,E*>::value << "\n";
    cout <<  "can_cast<E*,F*> = " << can_cast<E*,F*>::value << "\n";

    cout <<  "has_RTTI<D*> = " << has_RTTI<D*>::value << "\n";
    cout <<  "has_RTTI<E*> = " << has_RTTI<E*>::value << "\n";
    cout <<  "has_RTTI<F*> = " << has_RTTI<F*>::value << "\n";
    
    
    cout <<  "use_dynamic_downcast<B*,D*> = " << use_dynamic_downcast<B*,D*>::value << "\n";
    cout <<  "use_static_downcast<B*,D*> = " << use_static_downcast<B*,D*>::value << "\n";
    cout <<  "use_conversion<D*,B*> = "      << use_conversion<D*,B*>::value << "\n";

    cout <<  "use_static_downcast<D*&,D*&> = " << use_static_downcast<D*&,D*&>::value << "\n";
    cout <<  "use_static_downcast<D*,E*> = " << use_static_downcast<D*,E*>::value << "\n";
    cout <<  "use_dynamic_downcast<D*&,E*> = " << use_dynamic_downcast<D*&,E*>::value << "\n";
    
    
    cout <<  "Access(D  as D&) --->" << AccessCasted<D&>::access(d)  << "\n";
    cout <<  "Access(D& as D&) --->" << AccessCasted<D&>::access(rD) << "\n";
    cout <<  "Access(B& as D&) --->" << AccessCasted<D&>::access(rB) << "\n";
    cout <<  "Access(D* as D*) --->" << AccessCasted<D*>::access(pD) << "\n";
    cout <<  "Access(B* as D*) --->" << AccessCasted<D*>::access(pB) << "\n";
    cout <<  "Access(D*& as D*&) --->" << AccessCasted<D*&>::access(rpD) << "\n";
    cout <<  "Access(B*& as D*&) --->" << AccessCasted<D*&>::access(rpB) << "\n";
    
    cout <<  "Access(D  as B&) --->" << AccessCasted<B&>::access(d)  << "\n";
    cout <<  "Access(D& as B&) --->" << AccessCasted<B&>::access(rD) << "\n";
    cout <<  "Access(B& as B&) --->" << AccessCasted<D&>::access(rB) << "\n";
    cout <<  "Access(D* as B*) --->" << AccessCasted<B*>::access(pD) << "\n";
    cout <<  "Access(B* as B*) --->" << AccessCasted<B*>::access(pB) << "\n";
    cout <<  "Access(D*& as B*&) --->" << AccessCasted<B*&>::access(rpD) << "\n";
    cout <<  "Access(B*& as B*&) --->" << AccessCasted<B*&>::access(rpB) << "\n";
    
    cout <<  "Access(D  as E&) --->" << AccessCasted<E&>::access(d) << "\n";
    cout <<  "Access(E& as F&) --->" << AccessCasted<F&>::access(rE) << "\n";
    cout <<  "Access(D(E)* as E*) --->" << AccessCasted<E*>::access(pDE) << "\n";
    cout <<  "Access(D(E)* as F*) --->" << AccessCasted<F*>::access(pDE) << "\n";
    cout <<  "Access(E* as F*) --->" << AccessCasted<F*>::access(pE) << "\n";

    cout <<  "\ngulp\n";
    
    
    return 0;
  }