G4CTCounter.hh

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//
// Author: Mathieu Karamitros

/*
 * Compile time counter to use flags with switch and add new flags
 *
 *   - Usage 1
 *
 * class A {
 *  G4CT_COUNT_INIT(0)
 *  CT_COUNT(a)
 *  CT_COUNT(b)
 *  CT_COUNT(c)
 * };
 *
 * class B1 : public A{
 *  CT_COUNT(d)
 * };
 *
 * class B2 : public A{
 *  CT_COUNT(e)
 * };
 * class C : public B1{
 *  CT_COUNT(f)
 * };
 *
 * Result
 *  a = 0
 *  b = 1
 *  c = 2
 *  d & e = 3
 *  f = 4
 *
 *   - Usage 2
 *  namespace CounterNSpace{
 *    G4CT_COUNT_INIT(0)
 *    CT_COUNT(a)
 *    CT_COUNT(b)
 *    CT_COUNT(c)
 *  }
 *
 *  // extend
 *  namespace CounterNSpace{
 *    CT_COUNT(d)
 *    CT_COUNT(e)
 *    CT_COUNT(f)
 *  }
 */

#ifndef G4CTCounter_h
#define G4CTCounter_h

template<int N>
struct G4Number: public G4Number<N-1>{
  static constexpr int value=N;
};

template<>
struct G4Number<0>{
  static constexpr int value=0;
};

//------------------------------------------------------------------------------

#define G4CT_COUNT_INIT(init_value)     \
  static constexpr G4Number<init_value> \
   Counter(G4Number<init_value>) {      \
     return G4Number<init_value>();     \
   }

#define G4CT_COUNT(flagName)                   \
  static constexpr const int flagName =        \
   decltype(Counter(G4Number<255>{}) )::value; \
  static constexpr G4Number<flagName + 1>      \
   Counter(G4Number<flagName + 1>){            \
     return G4Number<flagName +1 >{};          \
   }

//------------------------------------------------------------------------------
// On Win platforms, static functions must not be inlined, use the following
// macros to separate definition and implementation of static function
// to avoid potential crashes

#define G4CT_COUNT_INIT_DEF(init_value) \
  static constexpr G4Number<init_value> \
   Counter(G4Number<init_value>);

#define G4CT_COUNT_INIT_IMPL(enumName, init_value) \
  constexpr G4Number<init_value> \
   enumName::Counter(G4Number<init_value>){ \
     return G4Number<init_value>{}; \
   }

#define G4CT_COUNT_DEF(flagName) \
  static constexpr const int flagName = \
   decltype(Counter(G4Number<255>{}))::value; \
  static constexpr G4Number<flagName + 1> \
   Counter(G4Number<flagName + 1>);

#define G4CT_COUNT_IMPL(enumName, flagName) \
  constexpr G4Number<enumName::flagName + 1> \
   enumName::Counter(G4Number<enumName::flagName + 1>){ \
     return G4Number<enumName::flagName +1 >{}; \
   }

//------------------------------------------------------------------------------

#endif