constructor

问题 I was reading this http://en.wikipedia.org/wiki/C%2B%2B0x#Modification_to_the_definition_of_plain_old_data It mentions trivial default constructor, trivial copy constructor, copy assignment operator, trivial destructor. What is trivial and not trivial? 回答1: In simple words a "trivial" special member function literally means a member function that does its job in a very straightforward manner. The "straightforward manner" means different thing for different kinds of special member functions.

问题 I am surprised to accidentally discover that the following works: #include <iostream> int main(int argc, char** argv) { struct Foo { Foo(Foo& bar) { std::cout << &bar << std::endl; } }; Foo foo(foo); // I can't believe this works... std::cout << &foo << std::endl; // but it does... } I am passing the address of the constructed object into its own constructor. This looks like a circular definition at the source level. Do the standards really allow you to pass an object into a function before

问题 This question already has answers here : Is there a good use case for the constructor property in Javascript? (3 answers) Closed 6 years ago . In JavaScript, every function's prototype object has a non-enumerable property constructor which points to the function (EcmaScript §13.2). It is not used in any native functionality (e.g. instanceof checks only the prototype chain), however we are encouraged to adjust it when overwriting the prototype property of a function for inheritance: SubClass

问题 What is the purpose of a constructor? I've been learning Java in school and it seems to me like a constructor is largely redundant in things we've done thus far. It remains to be seen if a purpose comes about, but so far it seems meaningless to me. For example, what is the difference between the following two snippets of code? public class Program { public constructor () { function(); } private void function () { //do stuff } public static void main(String[] args) { constructor a = new

问题 How can you construct objects passing arguments directly to your own classes? Something like this: Dim this_employee as Employee Set this_employee = new Employee(name:="Johnny", age:=69) Not being able to do this is very annoying, and you end up with dirty solutions to work this around. 回答1: Here's a little trick I'm using lately and brings good results. I would like to share with those who have to fight often with VBA. 1.- Implement a public initiation subroutine in each of your custom

问题 For winforms applications I'm wondering what setup code should go in: MainForm() as opposed to MainForm_Load(object sender, EventArgs e) Are there any best practice guidelines here? 回答1: Programmers that have worked with VB6 tend to put a lot of code in the Load event, in VB6 that event was used to initialize the form. But that's not appropriate anymore in Windows Forms, the Form class can have a constructor. The .NET way is to initialize class objects in the constructor, there are very few

问题 This question already has answers here : How to invoke the super constructor in Python? (7 answers) Closed 3 years ago . Consider this - a base class A, class B inheriting from A, class C inheriting from B. What is a generic way to call a parent class initialiser in an initialiser? If this still sounds too vague, here's some code. class A(object): def __init__(self): print "Initialiser A was called" class B(A): def __init__(self): super(B,self).__init__() print "Initialiser B was called"

问题 You can't put two __construct functions with unique argument signatures in a PHP class. I'd like to do this: class Student { protected $id; protected $name; // etc. public function __construct($id){ $this->id = $id; // other members are still uninitialized } public function __construct($row_from_database){ $this->id = $row_from_database->id; $this->name = $row_from_database->name; // etc. } } What is the best way to do this in PHP? 回答1: I'd probably do something like this: <?php class Student

问题 Given a function: function x(arg) { return 30; } You can call it two ways: result = x(4); result = new x(4); The first returns 30, the second returns an object. How can you detect which way the function was called inside the function itself ? Whatever your solution is, it must work with the following invocation as well: var Z = new x(); Z.lolol = x; Z.lolol(); All the solutions currently think the Z.lolol() is calling it as a constructor. 回答1: NOTE: This is now possible in ES2015 and later.

问题 In C++, Aside from dynamic memory allocation, is there a functional difference between the following two lines of code: Time t (12, 0, 0); //t is a Time object Time* t = new Time(12, 0, 0);//t is a pointer to a dynamically allocated Time object I am assuming of course that a Time(int, int, int) ctor has been defined. I also realize that in the second case t will need to be deleted as it was allocated on the heap. Is there any other difference? 回答1: The line: Time t (12, 0, 0); ... allocates a