Overriding essentially means that either the Base class method or the Derived class method will be called at run-time depending on the actual object pointed by the pointer. It implies that: i.e: Every place where the Base class method can be called can be replaced by call to Derived class method without any change to … Read more
Approach 1 (Virtual Function) “+” The “correct way to do it in C++ “-” A new class must be created per callback “-” Performance-wise an additional dereference through VF-Table compared to Function Pointer. Two indirect references compared to Functor solution. Approach 2 (Class with Function Pointer) “+” Can wrap a C-style function for C++ Callback … Read more
The rationale that you included is reasonably clear: naturally, virtual functions are meant to be overridden by subclasses, so you as the designer of the base class should make it as easy as possible for people who inherit your class to provide a suitable override. However, if you use auto, figuring out the return type … Read more
[syserr.errcat.overview] has std::error_category class error_category { virtual const char* name() const noexcept = 0; virtual string message(int ev) const = 0; }; There are no others in C++14.
We cannot modify the access modifiers when overriding a virtual method in derived class. That statement is false. You can and must change the access modifiers when in precisely the situation you describe. In other situations you must not change the access modifiers. I refer you to section 10.6.4 of the specification, which states: an … Read more
Yep, you are misunderstanding a little. The method of the same name on the derived class will hide the parent method in this case. You would imagine that if this weren’t the case, trying to create a method with the same name as a base class non-virtual method should throw an error. It is allowed … Read more
Calling virtual functions from a constructor or destructor is dangerous and should be avoided whenever possible. All C++ implementations should call the version of the function defined at the level of the hierarchy in the current constructor and no further. The C++ FAQ Lite covers this in section 23.7 in pretty good detail. I suggest … Read more
What is function hiding? … is a form of name hiding. A simple example: void foo(int); namespace X { void foo(); void bar() { foo(42); // will not find `::foo` // because `X::foo` hides it } } This also applies to the name lookup in a base class: class Base { public: void foo(int); }; … Read more
You can’t do it directly, but there are a couple of ways to simulate it, with the help of the Non-Virtual Interface idiom. Use covariance on raw pointers, and then wrap them struct Base { private: virtual Base* doClone() const { … } public: shared_ptr<Base> Clone() const { return shared_ptr<Base>(doClone()); } virtual ~Base(){} }; struct … Read more
I didn’t find any answer, so here is the performance test: using System; using System.Diagnostics; using System.Linq.Expressions; using System.Reflection; using System.Reflection.Emit; namespace ExpressionTest { public interface IFoo { int Bar(); } public sealed class FooImpl : IFoo { public int Bar() { return 0; } } class Program { static void Main(string[] args) { var … Read more