UML Short Introduction

Interface

• Does not implement anything

• C++: abstract base class

• Purest form (preferred): no implementation of anything

• Implementation inheritance is possible though, but should not be overused

class Sensor
{
public:
    virtual ~Sensor() {}

    virtual double get_temperature() = 0;
};

Interface Implementation, Inheritance

• I2CSensor is-a Sensor

• I2CSensor can-be-used-as-a Sensor (e.g. pointer assignment)

class I2CSensor : public Sensor
{
public:
    I2CSensor(unsigned int bus, uint8_t address);

    double get_temperature() override;
};

Connectors: Association, Aggregation, Composition

• Several forms of knows-a

• Describes using-relationships between types

Association

• Lightest form

• Usually implemented as raw pointer relationship

• Lifetime and resource management unspecified

class PIDController
{
// ...
private:
    Sensor* _sensor;
    Switch* _switch;
};

Aggregation

• Semi has-a

• Often implemented as std::shared_ptr<>

class PIDController
{
// ...
private:
    std::shared_ptr<Sensor> _sensor;
    std::shared_ptr<Switch> _switch;
};

Composition

• Most-defined form

• Commonly implemented as

  • Automatic membership

  • std::unique_ptr<>

class PIDController
{
// ...
private:
    Sensor _sensor;
    Switch _switch;
};

class PIDController
{
// ...
private:
    std::unique_ptr<Sensor> _sensor;
    std::unique_ptr<Switch> _switch;
};