class IBase
{
public:
    virtual void processAction(void *data) = 0; // pure virtual
}

class Worker: public IBase
{
public:
    virtual void processAction(void *data)
    {
        // define logic
    }
}

class Base
{
public:
    virtual void processAction(void *data) {}
}

class Worker: public Base
{
public:
    virtual void processAction(void *data) override
    {
        // define logic
    }
}