Is there a conceivable design pattern for any object-oriented program? I ask this because recently I saw an implementation of a Door class with a Lock. It was part of a test and the answer said that the code is following the Null Object pattern:
class Lock
{
public:
virtual void close() = 0;
virtual void open() = 0;
virtual bool is_open() const = 0;
virtual ~Lock() { }
};
class DummyLock
: public Lock
{
private:
DummyLock();
DummyLock(const DummyLock&) = delete;
DummyLock& operator=(const DummyLock&) = delete;
private:
void close() { }
void open() { }
bool is_open() const { return true; }
public:
static DummyLock m_instance;
};
class Door
{
public:
Door() : m_lock(DummyLock::m_instance) { }
Door(Lock &lock) : m_lock(lock) { }
public:
Lock& get_lock() const { return m_lock; }
private:
Lock &m_lock;
};
This made me think: This code follows a good design pattern even though the description is so simple (this class is designing a door class with a lock), so if I am writing more complex code, should there always be some design pattern that I am following?
