On invoking overridable method from constructors Simply put, this is wrong because it unnecessarily opens up possibilities to MANY bugs. When the @Override is invoked, the state of the object may be inconsistent and/or incomplete. A quote from Effective Java 2nd Edition, Item 17: Design and document for inheritance, or else prohibit it: There are … Read more
A much neater way to get ‘alternate constructors’ is to use classmethods. For instance: >>> class MyData: … def __init__(self, data): … “Initialize MyData from a sequence” … self.data = data … … @classmethod … def fromfilename(cls, filename): … “Initialize MyData from a file” … data = open(filename).readlines() … return cls(data) … … @classmethod … … Read more
Foo(int num): bar(num) This construct is called a Member Initializer List in C++. Simply said, it initializes your member bar to a value num. What is the difference between Initializing and Assignment inside a constructor? Member Initialization: Foo(int num): bar(num) {}; Member Assignment: Foo(int num) { bar = num; } There is a significant difference … Read more
Since it is not possible to make an async constructor, I use a static async method that returns a class instance created by a private constructor. This is not elegant but it works ok. public class ViewModel { public ObservableCollection<TData> Data { get; set; } //static async method that behave like a constructor async public … Read more
In C++ the only difference between a class and a struct is that members and base classes are private by default in classes, whereas they are public by default in structs. So structs can have constructors, and the syntax is the same as for classes.
With ECMAScript5’s Function.prototype.bind things get pretty clean: function newCall(Cls) { return new (Function.prototype.bind.apply(Cls, arguments)); // or even // return new (Cls.bind.apply(Cls, arguments)); // if you know that Cls.bind has not been overwritten } It can be used as follows: var s = newCall(Something, a, b, c); or even directly: var s = new (Function.prototype.bind.call(Something, null, … Read more
In line with the other answers, there are multiple ways to call super class methods (including the constructor), however in Python-3.x the process has been simplified: Python-3.x class A(object): def __init__(self): print(“world”) class B(A): def __init__(self): print(“hello”) super().__init__() Python-2.x In python 2.x, you have to call the slightly more verbose version super(<containing classname>, self), which … Read more
TypeScript allows you to declare overloads but you can only have one implementation and that implementation must have a signature that is compatible with all overloads. In your example, this can easily be done with an optional parameter as in, interface IBox { x : number; y : number; height : number; width : number; … Read more
You can’t. It’s occasionally a pain, but you wouldn’t be able to call it using normal techniques anyway. In a blog post I’ve suggested static interfaces which would only be usable in generic type constraints – but could be really handy, IMO. One point about if you could define a constructor within an interface, you’d … Read more
The parent class’ constructor needs to be called before the subclass’ constructor. This will ensure that if you call any methods on the parent class in your constructor, the parent class has already been set up correctly. What you are trying to do, pass args to the super constructor is perfectly legal, you just need … Read more