#include // Interface that has 2 methods, one for swichting the light on and one for switching off. // C++ interfaces *must* always have a virtual empty destructor, else you risk getting resource // leaks in your code! class iLightSwitch { public: virtual ~iLightSwitch() {}; virtual void SwitchOn() = 0; virtual void SwitchOff() = 0; }; // Light simulator, as I don't have real hardware in this environment class LightSimulator: public iLightSwitch { public: void SwitchOn() { std::cout << "LightSimulator: switched light ON\n"; }; void SwitchOff() { std::cout << "LightSimulator: switched light OFF\n"; }; }; // Just some random class that needs to switch lights on and off class MyHardwareThingie { public: MyHardwareThingie(iLightSwitch& lightswitch) // an implementation for iLightSwitch is given at construction time : lightswitch(lightswitch) { }; void DoIt() { lightswitch.SwitchOn(); // where needed, I simply call interface methods without actually lightswitch.SwitchOff(); // knowing *what* I am calling (real hardware, simulator, mock, ...) }; private: iLightSwitch& lightswitch; }; int main() { std::cout << "Demo that shows usage of dependency injection\n"; std::cout << "Dependency injection is used for hardware abstraction,\n"; std::cout << "which has the following advantages:\n"; std::cout << "- I can simply use a simulator if I don't have hardware\n"; std::cout << "- if the hardware ever changes, I only need to implement\n"; std::cout << " a new implementation of the interface to support the\n"; std::cout << " new hardware, the rest of the system stays the same!\n"; std::cout << "- I can use mocks to unit test my class without having\n"; std::cout << " an implementation at all!\n\n"; std::cout << "Demo: calling DoIt that switches the light on and off:\n\n"; LightSimulator simulator; MyHardwareThingie demo(simulator); // I give an interface implementation to the class at construction demo.DoIt(); return 0; }

DependencyInjection_C++