makeWatchFunc.h

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#ifndef art_Framework_Services_Registry_detail_makeWatchFunc_h
#define art_Framework_Services_Registry_detail_makeWatchFunc_h

#include <functional>
#include <type_traits>

// makeWatchFunc
//
// Construct the correct lambda to allow general registration of
// pointer-to-member callback functions for global and local signals.
namespace art {
  namespace detail {
    template <typename T, typename ResultType, typename... Args>
    std::function<ResultType(Args...)>
    makeWatchFunc(ResultType (T::*slot)(Args...), T& t)
    {
      return [slot, &t](Args&&... args) -> ResultType {
        return (t.*slot)(std::forward<Args>(args)...);
      };
    }

    template <typename T, typename ResultType, typename... Args>
    std::function<ResultType(Args...)>
    makeWatchFunc(ResultType (T::*slot)(Args...) const, T const& t)
    {
      return [slot, &t](Args&&... args) -> ResultType {
        return (t.*slot)(std::forward<Args>(args)...);
      };
    }
  }
}
#endif /* art_Framework_Services_Registry_detail_makeWatchFunc_h */

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