SumSecondFunction.h

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#ifndef Utilities_SumSecondFunction_h
#define Utilities_SumSecondFunction_h

#include <functional>

namespace util {

  template < typename _Key, typename _Value, typename _BinaryOperation = std::plus<_Value> >
  class SumSecondFunction
    : public std::binary_function< _Value,
                                   std::pair<_Key, _Value>,
                                   _Value >
  {
  public:
    const _Value operator() ( const _Value& value,
                              const std::pair<_Key, _Value>& entry ) const
    {
      return _BinaryOperation()( value, entry.second );
    }
  };

} // namespace util

#endif // Utilities_SumSecondFunction_h