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CdbType2Id.hh

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#ifndef CDB_TYPE_2_ID_HH
#define CDB_TYPE_2_ID_HH

// File and Version Information:
//      $Id: CdbType2Id.hh,v 1.1 2005/03/01 21:15:29 gapon Exp $

#include "CdbBase/CdbCommon.hh"

/// The default generator of unique type identifiers (a utility class)
/**
  * The generator will produce unsigned integer numbers starting with 0 every
  * time the CdbDefaultTypeIdGenerator::next() method is invoked.
  *
  * The class is used in the unique mapping scheme between C++ types and numbers.
  *
  * IMPORTANT DESIGN NOTE:
  *
  *   That the mapping can't be persistent or it can't be used in any way beyong
  *   the lifespan of a process.
  *
  * @see class CdbType2Id
  */
class CdbDefaultTypeIdGenerator {

public:

  /// Produce the next unique number
  /**
    * The first time the method gets called it will produce 0.
    */
    static unsigned int next( )
    {
        static unsigned int current = 0;
        return current++;
    }
};

/// Translate the type into its identifier
/**
  * This class will use the specified (or the default) generator of identifiers.
  * A reson why we may want to parameterize the current class with different
  * generators is that we may want to have a better control over actual number
  * of identifiers associated with transient types. For example, we may consider
  * using predefined type numbers rather than automatically generated ones. Or,
  * we may want to have two independent collections of transient types whose
  * identifiers both start with 0.
  */
template< class T,
          class GENERATOR = CdbDefaultTypeIdGenerator >
class CdbType2Id {

public:

  /// The type to be mapped to its id

    typedef T type;

public:

  /// Get the identifier corresponding to the type

    static unsigned int id( )
    {
        static unsigned int value = GENERATOR::next( );
        return value;
    }
};

#endif  // CDB_TYPE_2_ID_HH

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