Design Pattern --- Command

class ReceiverA
{
public:
    // Interface.
    void Action() { cout <<"ReceiverA::Action()." <<endl; }
};
class ReceiverB
{
public:
    // Interface.
    void Action() { cout <<"ReceiverB::Action()." <<endl; }
};

class Command
{
public:
    virtual ~Command(){}
public:
    // Interface.
    virtual void Execute() = 0;
};
class CommandA : public Command
{
    // data.
    ReceiverA &m_receiver;

public:
    CommandA(ReceiverA ra) : m_receiver(ra) {}
public:
    // Interface.
    virtual void Execute() override { m_receiver.Action(); }
};
class CommandB : public Command
{
    // data.
    ReceiverB &m_receiver;

public:
    CommandB(ReceiverB rb) : m_receiver(rb) {}
public:
    // Interface.
    virtual void Execute() override { m_receiver.Action(); }
};

int main(int argc, char *argv[])
{
    ReceiverA ra;
    ReceiverB rb;
    Command *ca = new CommandA(ra),
            *cb = new CommandB(rb);

    ca->Execute();            // 此时, 调用者无需区分执行的内容, 只需要调用 Execute 即可.
    cb->Execute();            // 此模式借助 Command 这个中间层, 在调用者 ('main' 函数) 和被调用者 ('ReceiverA' 和 'ReceiverB') 之间解耦.

    // TODO: Release memory.

    return 0;
}