chapter04_04a

Example Chapter04_04a

LED Objects and Polymorphism via References

Example chapter04_04a implements the same basic functionality as does example chapter04_04. Example chapter04_04a, however, uses an std::array of LED base class references instead of base class pointers in order to exercise object oriented polymorphism.

Application Description

The LED base class references are stored within template instances of std::reference_wrapper from the <functional> library. This is because C++ can not store references in STL containers such as std::array.

The container of wrapped LED base class references looks like this:

#include <functional>

// ...

using app_led_ref_type = std::reference_wrapper<mcal::led::led_base>;

std::array<app_led_ref_type, 5U> app_led_base_class_refs =
{{
  mcal::led::led0(),
  mcal::led::led1(),
  mcal::led::led2(),
  mcal::led::led3(),
  mcal::led::led4()
}};

The elements in the array of LED base class references are toggled in the application task each second in the following fashion.

void app::led::task_func()
{
  if(app_led_timer.timeout())
  {
    app_led_timer.start_interval(app_led_one_sec);

    for(typename app_led_ref_type::type& led : app_led_base_class_refs)
    {
      led.toggle();
    }

    app_led_state_is_on = (!app_led_state_is_on);
  }
}

Hardware Setup

The hardware setup for example chapter04_04a is the same as that of example chapter04_04.