text: #ifndef __SONARIMPL__
  #define __SONARIMPL__
  
  #include "Sonar.h"
  
  class SonarImpl: public Sonar {
  
  public:
      SonarImpl(int trigPin, int echoPin);
      float getDistance();
  
  private:
      /* TEMPERATURE = 20 °C */
      const float vs = 331.5 + 0.6*20;
      int trigPin;
      int echoPin;
  };
  
  #endif
  