It is because name lookup stops if it finds a name in one of your bases. It won’t look beyond in other bases. The function in B shadows the function in A. You have to re-declare the function of A in the scope of B, so that both functions are visible from within B and … Read more
TL;DR Extra parentheses change the meaning of a C++ program in the following contexts: preventing argument-dependent name lookup enabling the comma operator in list contexts ambiguity resolution of vexing parses deducing referenceness in decltype expressions preventing preprocessor macro errors Preventing argument-dependent name lookup As is detailed in Annex A of the Standard, a post-fix expression … Read more
Warning: this is a really long explanation, but hopefully it really explains not only what SFINAE does, but gives some idea of when and why you might use it. Okay, to explain this we probably need to back up and explain templates a bit. As we all know, Python uses what’s commonly referred to as … Read more
You have to understand the forwarding problem. You can read the entire problem in detail, but I’ll summarize. Basically, given the expression E(a, b, … , c), we want the expression f(a, b, … , c) to be equivalent. In C++03, this is impossible. There are many attempts, but they all fail in some regard. … Read more
Because dynamic_cast can only downcast polymorphic types, so sayeth the Standard. You can make your class polymoprphic by adding a virtual destructor to the base class. In fact, you probably should anyway (See Footnote). Else if you try to delete a B object through an A pointer, you’ll evoke Undefined Behavior. class A { public: … Read more
The four operators mentioned in the original posting, =, (), -> and [], must indeed be implemented as non-static member functions (by respectively C++98 §13.5.3/1, §13.5.4/1, §13.5.5/1 and §13.5.6/1). Bjarne Stroustrup’s rationale was, as I recall from earlier debates on the subject, to retain some sanity in the language, i.e. having at least some things … Read more
All you need to do is declare the class’ new operator private: class X { private: // Prevent heap allocation void * operator new (size_t); void * operator new[] (size_t); void operator delete (void *); void operator delete[] (void*); // … // The rest of the implementation for X // … }; Making ‘operator new’ … Read more
There are two distinct forms of “properties” that turn up in the standard library, which I will categorise as “Identity oriented” and “Value oriented”. Which you choose depends on how the system should interact with Foo. Neither is “more correct”. Identity oriented class Foo { X x_; public: X & x() { return x_; } … Read more
It is useful when you want to have access to some members of the base class, but without exposing them in your class interface. Private inheritance can also be seen as some kind of composition: the C++ faq-lite gives the following example to illustrate this statement class Engine { public: Engine(int numCylinders); void start(); // … Read more
I want to pass a shared pointer to a function. Can you help me with that? Sure, I can help with you that. I assume you have some understanding of ownership semantics in C++. Is that true? Yeah, I’m reasonably comfortable with the subject. Good. Ok, I can only think of two reasons to take … Read more