基本上，不是协议"而是具有纯虚函数的基类"，有时在其他语言中也称为接口.

Basically, instead of "Protocol" think "base class with pure virtual functions", sometimes called an interface in other languages.

class Protocol
{
public:
    virtual void Foo() = 0;
};

class Class : public Protocol
{
public:
    void Foo() { }
};

class Class2 : public Protocol
{
public:
    void Foo() { }
};

class TableView
{
public:
    void setDelegate(Protocol* proto) { }
};