There is no in-built solution for this in JavaScript. An alternative solution can be using the arguments object (in some cases), or passing your own configuration options, similar to this: const defaults = { numberWheels: 4, color: “black”, name: “myCar” } class Car { constructor(options) { this.wheelsNum = options.numberWheels || defaults.numberWheels; this.name = options.name || … Read more
You can’t have your cake and eat it too. If the object has a constructor it is no longer an aggregate, and only aggregates can be initialized with designated initializers. You can’t use constructors for arbitrary initialization logic with aggregates. Are we toasted though? No, because there’s the “named constructor” idiom. It’s essentially just a … Read more
Comma operator to the rescue! An expression (a, b) will evaluate a first, then b. class DisplayOpenGL { public: DisplayOpenGL(HWND hwnd) : m_device(hwnd), m_opengl((m_device.SetPixelFormat(), m_device)) { }; private: DeviceContext m_device; OpenGLContext m_opengl; };
It’ll be 2. Constructors run in order from base class first to inherited class last. Note that initialisers (both static and instance variables) run in the opposite direction. The full sequence is here: http://www.csharp411.com/c-object-initialization/
This is a little confusing: constructors indeed do not return a value; it is operator new that does. However, constructors are always used with a new*, so it looks like they always return a value. * This is a slight simplification: you can use a constructor without new if you go through reflection. However, the … Read more
New answer (nine years later) There is now several overloads for Activator.CreateInstance that allow you to use non public constructors: Activator.CreateInstance(typeof(YourClass), true); true = use non public constructors. . Old answer Default constructors are private for a reason. The developer doesn’t make it private for fun. But if you still want to use the default … Read more
Starting from C++17 there’s no difference whatsoever. There’s one niche use case where the std::vector = std::vector initialization syntax is quite useful (albeit not for default construction): when one wants to supply a “count, value” initializer for std::vector<int> member of a class directly in the class’s definition: struct S { std::vector<int> v; // Want to … Read more
Try adding square brackets after new MyClass and a semi-colon at the end MyClass[] testobjlist = new MyClass[] { new MyClass(1001,1234,”Text 1″, “abcdefghijklm”, “ding”), new MyClass(1002,2345,”Text xx”, “bla bla”, “dong”), new MyClass(1003,8653,”Text yy”, “blah blah even more”, “bamm!”) };
(This answer applies to C# and Java. I believe C++ works differently on this matter.) Calling a virtual method in a constructor is indeed dangerous, but sometimes it can end up with the cleanest code. I would try to avoid it where possible, but without bending the design hugely. (For instance, the “initialize later” option … Read more