Typically final will not be used on the base class’ definition of a virtual function. final will be used by a derived class that overrides the function in order to prevent further derived types from further overriding the function. Since the overriding function must be virtual normally it would mean that anyone could override that … Read more
final does not require the function to override anything in the first place. Its effect is defined in [class.virtual]/4 as If a virtual function f in some class B is marked with the virt-specifier final and in a class D derived from B a function D::f overrides B::f, the program is ill-formed. That’s it. Now … Read more
In C# you have to mark method as virtual to make it possible to override. Does it mean that in C# you should mark all methods virtual (except a few ones that you don’t want to be overridden), since most likely you don’t know in what way your class can be inherited? No. If the … Read more
The assignment operator is not required to be made virtual. The discussion below is about operator=, but it also applies to any operator overloading that takes in the type in question, and any function that takes in the type in question. The below discussion shows that the virtual keyword does not know about a parameter’s … Read more
In some cases, yes, it is legal for a derived class to override a virtual function using a different return type as long as the return type is covariant with the original return type. For example, consider the following: class Base { public: virtual ~Base() {} virtual Base* clone() const = 0; }; class Derived: … Read more
Since g++ 4.7 it does understand the new C++11 override keyword: class child : public parent { public: // force handle_event to override a existing function in parent // error out if the function with the correct signature does not exist void handle_event(int something) override; };
Classes should be designed for inheritance to be able to take advantage of it. Having methods virtual by default means that every function in the class can be plugged out and replaced by another, which is not really a good thing. Many people even believe that classes should have been sealed by default. virtual methods … Read more
Sure, and you don’t even have to define a method in the base class. In Python methods are better than virtual – they’re completely dynamic, as the typing in Python is duck typing. class Dog: def say(self): print “hau” class Cat: def say(self): print “meow” pet = Dog() pet.say() # prints “hau” another_pet = Cat() … Read more
For the interface, the addition of the abstract, or even the public keywords would be redundant, so you omit them: interface MyInterface { void Method(); } In the CIL, the method is marked virtual and abstract. (Note that Java allows interface members to be declared public abstract). For the implementing class, there are some options: … Read more
I ran some timings on a 3ghz in-order PowerPC processor. On that architecture, a virtual function call costs 7 nanoseconds longer than a direct (non-virtual) function call. So, not really worth worrying about the cost unless the function is something like a trivial Get()/Set() accessor, in which anything other than inline is kind of wasteful. … Read more