(P13) use of final keyword

1.final Modify function

• hold final Think it's a one size fits all approach
  If you use final Modify function , Only virtual functions can be modified , This prevents the subclass from overriding the function of the parent class ：

class Base
{
    
public:
    virtual void test()
    {
    
        cout << "Base class...";
    }
};

class Child : public Base
{
    
public:
    void test() final
    {
    
        cout << "Child class...";
    }
};

class GrandChild : public Child
{
    
public:
    //  Grammar mistakes ,  Rewriting is not allowed 
    void test()
    {
    
        cout << "GrandChild class...";
    }
};

• There are three classes in the above code ：

Base class ：Base
Subclass ：Child
Grandchildren ：GrandChild

• test() Is a virtual function in the base class , Override this method in a subclass , But I don't want to continue to rewrite this method in my grandchildren , Therefore, in subclasses test() The method is marked final, There is only one use of this method in grandchildren .

2.final decorator

Use final Keyword decorated classes are not allowed to be inherited , In other words, this class cannot have derived classes .

• Child Class is final Decorated , therefore Child Class does not allow derived classes GrandChild Class inheritance is illegal ,Child It's a kind of broken offspring .

class Base
{
    
public:
    virtual void test()
    {
    
        cout << "Base class...";
    }
};

class Child final: public Base
{
    
public:
    void test()
    {
    
        cout << "Child class...";
    }
};

// error,  Grammar mistakes 
class GrandChild : public Child
{
    
public:
};

• link ：final and override