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>>
  struct SumSecondFunction {
    _Value operator()(const _Value& value, const std::pair<_Key, _Value>& entry) const
    {
      return _BinaryOperation{}(value, entry.second);
    }
  };

} // namespace util

#endif // Utilities_SumSecondFunction_h