`final`¶

Architectural Decisions ¶

Interfaces are cool (“pure virtual”): add readability and specifiability
Implementation inheritance (extension) is not so cool
- One always has to ask: “Does somebody derive from this class?”
- ⟶ Architectural incontinence!

Enter `final`: Architectural Cleanliness By Compiler ¶

Best thing to do (IMHO): mark entire class final

code/c++11-final-class.cpp¶

class Leaf final {};
class Impossible : public Leaf {};

code/c++11-final-class.cpp:2:7: error: cannot derive from ‘final’ base ‘Leaf’ in derived type ‘Impossible’
    2 | class Impossible : public Leaf {};
      |       ^~~~~~~~~~

Also possible: marking single method final

code/c++11-final-method.cpp¶

class Base
{
public:
    virtual void method1() final {}
    virtual void method2() {}
};

class Derived : public Base
{
public:
    virtual void method1() final {}
    virtual void method2() {}
};

code/c++11-final-method.cpp:11:18: error: virtual function ‘virtual void Derived::method1()’ overriding final function
   11 |     virtual void method1() final {}
      |                  ^~~~~~~
code/c++11-final-method.cpp:4:18: note: overridden function is ‘virtual void Base::method1()’
    4 |     virtual void method1() final {}
      |                  ^~~~~~~