service_locator.h

#pragma once
 
#include <type_traits>
 
namespace core
{
template<class T, class TNull>
class Locator
{
    static_assert(std::is_base_of<T, TNull>::value, "TNull has to be a subtype of T");
public:
    static T& get()
    {
        return *service_;
    }
 
    static void provide(T* service)
    {
        if (service == nullptr)
        {
            // Revert to null service.
            service_ = &nullService_;
        } else
        {
            service_ = service;
        }
    }
 
protected:
    static T* service_;
    static TNull nullService_;
};
 
template<class T, class TNull> TNull Locator<T, TNull>::nullService_;
template<class T, class TNull> T* Locator<T, TNull>::service_ = &Locator<T, TNull>::nullService_;
 
 
}