Interface

推荐先阅读The-interface-principle.md，以获得对C++中interface的全面了解: C++中，interface不仅仅局限于OOP，它的ADL，使得interface可以拓展到非method。

CppCoreGuidelines I: Interfaces

stackoverflow How do you declare an interface in C++?

A

Make a class with pure virtual methods. Use the interface by creating another class that overrides those virtual methods.

A pure virtual method is a class method that is defined as virtual and assigned to 0.

class IDemo
{
    public:
        virtual ~IDemo() {} //将此函数声明成了
        virtual void OverrideMe() = 0;
};

class Child : public IDemo
{
    public:
        virtual void OverrideMe()
        {
            //do stuff
        }
};

A

To expand on the answer by bradtgmurray, you may want to make one exception（例外） to the pure virtual method list of your interface by adding a virtual destructor. This allows you to pass pointer ownership to another party without exposing the concrete derived class（这句话解释了将destructor声明为virtual和inline的目的：这允许您将指针所有权传递给另一方，而不会暴露具体的派生类）. The destructor doesn't have to do anything, because the interface doesn't have any concrete members. It might seem contradictory（自相矛盾） to define a function as both virtual and inline, but trust me - it isn't.

class IDemo
{
    public:
        virtual ~IDemo() {}
        virtual void OverrideMe() = 0;
};

class Parent
{
    public:
        virtual ~Parent();
};

class Child : public Parent, public IDemo
{
    public:
        virtual void OverrideMe()
        {
            //do stuff
        }
};

You don't have to include a body for the virtual destructor(因为它是inline的) - it turns out some compilers have trouble optimizing an empty destructor and you're better off using the default.