No, you don’t have to. Assume you have the following classes. class a { let name: String init() { name = “james” } } class b: a { let title: String override init() { title = “supervisor” } } If you instantiate a variable with let myVar = b() Then, override init() in b will … Read more
(1) The topmost class in the hierarchy looks like: template <typename T> class A { public: void bar() const { // do something and then call foo (possibly) in the derived class: foo(); } void foo() const { static_cast<const T*>(this)->foo(); } protected: ~A() = default; // Constructors should be protected as well. }; A<T>::foo() behaves … Read more
Good nice question. I really wish that the Standard was a little more explicit about what the intended usage is. Maybe there should be a C++ Rationale document that sits alongside the language standard. In any case, here is the approach that I use: (a) I’m not aware of the existence of any such list. … Read more
The short answer for this is, “because that’s what the C++ standard specifies”. Note that you can always specify a constructor that’s different from the default, like so: class Shape { Shape() {…} //default constructor Shape(int h, int w) {….} //some custom constructor }; class Rectangle : public Shape { Rectangle(int h, int w) : … Read more
2) Are there any technical reasons you can think of that would preclude “perfect forwarding constructors” from being an adequate alternative? I have shown one problem with that perfect forwarding approach here: Forwarding all constructors in C++0x . Also, the perfect forwarding approach can’t “forward” the expliciteness of base-class constructors: Either it is always a … Read more
JAXB is a spec, specific implementations will provide extension points to do things such as this. If you are using EclipseLink JAXB (MOXy) you could modify the Shape class as follows: import javax.xml.bind.annotation.XmlAttribute; import org.eclipse.persistence.oxm.annotations.XmlCustomizer; @XmlCustomizer(ShapeCustomizer.class) public abstract class Shape { int points; @XmlAttribute public int getPoints() { return points; } public void setPoints(int points) … Read more
You are actually attempting the impossible. The very heart of the matter is simple: virtual and template do not mix well. template is about compile-time code generation. You can think of it as some kind of type-aware macros + a few sprinkled tricks for meta programming. virtual is about runtime decision, and this require some … Read more
Here comes the black magic: class Program { static void Main() { IFoo foo = new IFoo(“black magic”); foo.Bar(); } } [ComImport] [Guid(“C8AEBD72-8CAF-43B0-8507-FAB55C937E8A”)] [CoClass(typeof(FooImpl))] public interface IFoo { void Bar(); } public class FooImpl : IFoo { private readonly string _text; public FooImpl(string text) { _text = text; } public void Bar() { Console.WriteLine(_text); } … Read more
This happens due to injected-class-name, unqualified name lookup rules and the fact the name lookup is completed before check for accessibility. injected-class-name is a mechanism that makes class name available inside that class definition. Now, the unqualified name lookup rules within a class definition state that first the scope of the class is searched, then … Read more
The field y is not declared by class Checks. Reading static fields doesn’t trigger initialization of the referenced class (Checks), unless that class is the one in which the field is declared (see JLS quote below). In this example, even if y is accessed through Checks, that will only trigger the initialization of Par because … Read more