user58538: Code would not update variable inside drive method. The variable is updated inside the drive method, but it doesn't change in the rest of the class. I wrote a simple similar method in normal C++ and the variable actually updated in the rest of the class.
engine.hpp
#pragma once
#include <Arduino.h>

namespace engine
{
class Engine
{
public:
    Engine(const unsigned char t_motor, const unsigned char t_forward, const unsigned char t_backward);
    void drive(unsigned int t_speed, bool t_isForward = true);
    bool isMovingForward() const;
    void stop();

private:
    const unsigned char m_motor;
    const unsigned char m_forward;
    const unsigned char m_backward;

    // Movements
    bool m_isActive;
    bool m_isForward;
    unsigned int m_speed;
};
} // namespace engine

engine.cpp init list
Engine::Engine(const unsigned char t_motor, const unsigned char t_forward, const unsigned char t_backward)
    : m_motor(t_motor),
      m_forward(t_forward),
      m_backward(t_backward),
      m_isActive(false),
      m_isForward(true),
      m_speed(0U)
{
}

drive method
void Engine::drive(unsigned int t_speed, bool t_isForward)
{

    if (!m_isActive || m_isForward != t_isForward)
    {
        stop();

        // Set direction
        if (t_isForward)
        {
            digitalWrite(m_forward, HIGH);
            digitalWrite(m_backward, LOW);
        }
        else
        {
            digitalWrite(m_forward, LOW);
            digitalWrite(m_backward, HIGH);
        }

        m_isActive = true;
        m_isForward = t_isForward;
    }

    if (m_speed != t_speed)
    {
        m_speed = t_speed; // Updated here
        analogWrite(m_motor, t_speed);
    }
}


user58538: I figured it out.
I was passing the engine objects as references instead of pointers.
main.cpp
// Engines
engine::Engine
    engine1(motors::Constants::MOTOR_1, motors::Constants::MOTOR_1_FORWARD, motors::Constants::MOTOR_1_BACKWARD),
    engine2(motors::Constants::MOTOR_2, motors::Constants::MOTOR_2_FORWARD, motors::Constants::MOTOR_2_BACKWARD),
    engine3(motors::Constants::MOTOR_3, motors::Constants::MOTOR_3_FORWARD, motors::Constants::MOTOR_3_BACKWARD),
    engine4(motors::Constants::MOTOR_4, motors::Constants::MOTOR_4_FORWARD, motors::Constants::MOTOR_4_BACKWARD);

engine_controller.cpp init list
EngineController::EngineController(engine::Engine &t_e1, engine::Engine &t_e2, engine::Engine &t_e3, engine::Engine &t_e4)
    : m_engine1(t_e1),
      m_engine2(t_e2),
      m_engine3(t_e3),
      m_engine4(t_e4),
      m_currentSpeed(EngineControllerConsts::MAX_SPEED),

      // Directions
      m_rights(0),
      m_lefts(0),

      m_rightDistance(-1),
      m_leftDistance(-1),

      m_lastForward(true),
      m_counter(0),

      m_lastForward1(true),
      m_lastForward2(true),
      m_turnsCounter(0)

{
}

The solution would be to use dynamic memory allocation.
main.cpp
// Engines
engine::Engine
    *engine1 = new engine::Engine(motors::Constants::MOTOR_1, motors::Constants::MOTOR_1_FORWARD, motors::Constants::MOTOR_1_BACKWARD),
    *engine2 = new engine::Engine(motors::Constants::MOTOR_2, motors::Constants::MOTOR_2_FORWARD, motors::Constants::MOTOR_2_BACKWARD),
    *engine3 = new engine::Engine(motors::Constants::MOTOR_3, motors::Constants::MOTOR_3_FORWARD, motors::Constants::MOTOR_3_BACKWARD),
    *engine4 = new engine::Engine(motors::Constants::MOTOR_4, motors::Constants::MOTOR_4_FORWARD, motors::Constants::MOTOR_4_BACKWARD);

engine_controller.cpp init list
EngineController::EngineController(
    engine::Engine *t_e1, engine::Engine *t_e2,
    engine::Engine *t_e3, engine::Engine *t_e4)
    : m_engine1(t_e1),
      m_engine2(t_e2),
      m_engine3(t_e3),
      m_engine4(t_e4),
      m_currentSpeed(EngineControllerConsts::MAX_SPEED),

      // Directions
      m_rights(0),
      m_lefts(0),

      m_rightDistance(-1),
      m_leftDistance(-1),

      m_lastForward(true),
      m_counter(0),

      m_lastForward1(true),
      m_lastForward2(true),
      m_turnsCounter(0)

{
}


58538: <p>Code would not update variable inside drive method. The variable is updated inside the drive method, but it doesn't change in the rest of the class. I wrote a simple similar method in normal C++ and the variable actually updated in the rest of the class.</p>

<p>engine.hpp</p>

<pre class="lang-cpp prettyprint-override"><code>#pragma once
#include &lt;Arduino.h&gt;

namespace engine
{
class Engine
{
public:
    Engine(const unsigned char t_motor, const unsigned char t_forward, const unsigned char t_backward);
    void drive(unsigned int t_speed, bool t_isForward = true);
    bool isMovingForward() const;
    void stop();

private:
    const unsigned char m_motor;
    const unsigned char m_forward;
    const unsigned char m_backward;

    // Movements
    bool m_isActive;
    bool m_isForward;
    unsigned int m_speed;
};
} // namespace engine
</code></pre>

<p>engine.cpp init list</p>

<pre class="lang-cpp prettyprint-override"><code>Engine::Engine(const unsigned char t_motor, const unsigned char t_forward, const unsigned char t_backward)
    : m_motor(t_motor),
      m_forward(t_forward),
      m_backward(t_backward),
      m_isActive(false),
      m_isForward(true),
      m_speed(0U)
{
}
</code></pre>

<p>drive method</p>

<pre class="lang-cpp prettyprint-override"><code>void Engine::drive(unsigned int t_speed, bool t_isForward)
{

    if (!m_isActive || m_isForward != t_isForward)
    {
        stop();

        // Set direction
        if (t_isForward)
        {
            digitalWrite(m_forward, HIGH);
            digitalWrite(m_backward, LOW);
        }
        else
        {
            digitalWrite(m_forward, LOW);
            digitalWrite(m_backward, HIGH);
        }

        m_isActive = true;
        m_isForward = t_isForward;
    }

    if (m_speed != t_speed)
    {
        m_speed = t_speed; // Updated here
        analogWrite(m_motor, t_speed);
    }
}
</code></pre>
 58538: <p>I figured it out.</p>

<p>I was passing the engine objects as references instead of pointers.</p>

<p>main.cpp</p>

<pre class="lang-cpp prettyprint-override"><code>// Engines
engine::Engine
    engine1(motors::Constants::MOTOR_1, motors::Constants::MOTOR_1_FORWARD, motors::Constants::MOTOR_1_BACKWARD),
    engine2(motors::Constants::MOTOR_2, motors::Constants::MOTOR_2_FORWARD, motors::Constants::MOTOR_2_BACKWARD),
    engine3(motors::Constants::MOTOR_3, motors::Constants::MOTOR_3_FORWARD, motors::Constants::MOTOR_3_BACKWARD),
    engine4(motors::Constants::MOTOR_4, motors::Constants::MOTOR_4_FORWARD, motors::Constants::MOTOR_4_BACKWARD);
</code></pre>

<p>engine_controller.cpp init list</p>

<pre class="lang-cpp prettyprint-override"><code>EngineController::EngineController(engine::Engine &amp;t_e1, engine::Engine &amp;t_e2, engine::Engine &amp;t_e3, engine::Engine &amp;t_e4)
    : m_engine1(t_e1),
      m_engine2(t_e2),
      m_engine3(t_e3),
      m_engine4(t_e4),
      m_currentSpeed(EngineControllerConsts::MAX_SPEED),

      // Directions
      m_rights(0),
      m_lefts(0),

      m_rightDistance(-1),
      m_leftDistance(-1),

      m_lastForward(true),
      m_counter(0),

      m_lastForward1(true),
      m_lastForward2(true),
      m_turnsCounter(0)

{
}
</code></pre>

<p>The solution would be to use dynamic memory allocation.</p>

<p>main.cpp</p>

<pre class="lang-cpp prettyprint-override"><code>// Engines
engine::Engine
    *engine1 = new engine::Engine(motors::Constants::MOTOR_1, motors::Constants::MOTOR_1_FORWARD, motors::Constants::MOTOR_1_BACKWARD),
    *engine2 = new engine::Engine(motors::Constants::MOTOR_2, motors::Constants::MOTOR_2_FORWARD, motors::Constants::MOTOR_2_BACKWARD),
    *engine3 = new engine::Engine(motors::Constants::MOTOR_3, motors::Constants::MOTOR_3_FORWARD, motors::Constants::MOTOR_3_BACKWARD),
    *engine4 = new engine::Engine(motors::Constants::MOTOR_4, motors::Constants::MOTOR_4_FORWARD, motors::Constants::MOTOR_4_BACKWARD);
</code></pre>

<p>engine_controller.cpp init list</p>

<pre class="lang-cpp prettyprint-override"><code>EngineController::EngineController(
    engine::Engine *t_e1, engine::Engine *t_e2,
    engine::Engine *t_e3, engine::Engine *t_e4)
    : m_engine1(t_e1),
      m_engine2(t_e2),
      m_engine3(t_e3),
      m_engine4(t_e4),
      m_currentSpeed(EngineControllerConsts::MAX_SPEED),

      // Directions
      m_rights(0),
      m_lefts(0),

      m_rightDistance(-1),
      m_leftDistance(-1),

      m_lastForward(true),
      m_counter(0),

      m_lastForward1(true),
      m_lastForward2(true),
      m_turnsCounter(0)

{
}
</code></pre>
