ResultChannel.hpp

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#ifndef ECHOMAP_RESULTCHANNEL_HPP
#define ECHOMAP_RESULTCHANNEL_HPP
 
#include <sigc++/signal.h>
 
#include <exception>
#include <stdexcept>
#include <type_traits>
#include <utility>
 
namespace echomap
{

template <class ResultT> class ResultChannel
{
public:
    template <class SlotT>
    [[nodiscard]] sigc::connection observe(
            SlotT&& slot
    )
    {
        return observers.connect(std::forward<SlotT>(slot));
    }

    template <class SlotT>
        requires(!std::is_const_v<ResultT>)
    [[nodiscard]] sigc::connection nominate_consumer(
            SlotT&& slot
    )
    {
        if (!consumer.empty())
            throw std::logic_error("Result channel already has a nominated consumer.");
 
        return consumer.connect(std::forward<SlotT>(slot));
    }
 
private:
    friend class WorkerResultDespatcher;
 
    using ObserverSignalT = sigc::signal<void(const ResultT&)>;
    using ConsumerSignalT = sigc::signal<void(ResultT&&)>;

    void publish(
            ResultT&& result
    )
    {
        std::exception_ptr observer_exception;
 
        // Emit const ResultT& to all observers.
        try {
            publish(result);
        } catch (...) {
            observer_exception = std::current_exception();
        }
 
        // If there is a nominated consumer, send it out.
        if (!consumer.empty())
            consumer.emit(std::move(result));
 
        if (observer_exception)
            std::rethrow_exception(observer_exception);
    }

    void publish(
            const ResultT& result
    )
    {
        observers.emit(result);
    }
 
    ObserverSignalT observers;
    ConsumerSignalT consumer;
};
 
} // namespace echomap
 
#endif // ECHOMAP_RESULTCHANNEL_HPP