ServiceWrapper.h

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#ifndef art_Framework_Services_Registry_detail_ServiceWrapper_h
#define art_Framework_Services_Registry_detail_ServiceWrapper_h
// vim: set sw=2 expandtab :

#include "art/Framework/Services/Registry/detail/ServiceWrapperBase.h"

#include <memory>
#include <type_traits>

namespace art {

  class ActivityRegistry;
  class ModuleDescription;
  class ProducingService;

  namespace detail {

    template <typename T>
    class ServiceWrapper;

    // If we have a constructor taking fhicl::ParameterSet const& and
    // ActivityRegistry&, use it. Otherwise, call a one-argument
    // constructor taking fhicl::ParameterSet const& only.
    template <typename T>
    std::enable_if_t<
      std::is_constructible_v<T, fhicl::ParameterSet const&, ActivityRegistry&>,
      std::shared_ptr<T>>
    makeServiceFrom(fhicl::ParameterSet const& ps, ActivityRegistry& areg)
    {
      static_assert(
        !std::is_base_of_v<ProducingService, T>,
        "\n\nart-error: A service that inherits from art::ProducingService\n"
        "           cannot have a constructor that takes an ActivityRegistry&\n"
        "           argument.  Contact artists@fnal.gov for guidance.\n");
      return std::make_shared<T>(ps, areg);
    }

    template <typename T>
    std::enable_if_t<!std::is_constructible_v<T,
                                              fhicl::ParameterSet const&,
                                              ActivityRegistry&>,
                     std::shared_ptr<T>>
    makeServiceFrom(fhicl::ParameterSet const& ps, ActivityRegistry&)
    {
      return std::make_shared<T>(ps);
    }

    template <typename T>
    class ServiceWrapper : public ServiceWrapperBase {
    public:
      ServiceWrapper(ServiceWrapper const&) = delete;
      ServiceWrapper& operator=(ServiceWrapper const&) = delete;

      ServiceWrapper(fhicl::ParameterSet const& ps, ActivityRegistry& areg)
        : service_ptr_{makeServiceFrom<T>(ps, areg)}
      {}

      explicit ServiceWrapper(std::shared_ptr<T>&& p) : service_ptr_{move(p)} {}

      T&
      get()
      {
        return *service_ptr_;
      }

      template <typename U,
                typename = std::enable_if_t<std::is_base_of_v<U, T>>>
      std::unique_ptr<ServiceWrapper<U>>
      getAs() const
      {
        return std::make_unique<ServiceWrapper<U>>(
          std::static_pointer_cast<U>(service_ptr_));
      }

    private:
      void
      registerProducts(ProductDescriptions& productsToProduce,
                       ProducingServiceSignals& signals,
                       ModuleDescription const& md) override
      {
        if constexpr (std::is_base_of_v<ProducingService, T>) {
          service_ptr_->registerCallbacks(signals);
          service_ptr_->setModuleDescription(md);
          service_ptr_->registerProducts(productsToProduce, md);
        }
      }

      std::shared_ptr<T> service_ptr_;
    };

  } // namespace detail
} // namespace art

#endif /* art_Framework_Services_Registry_detail_ServiceWrapper_h */

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