constructor

问题 I am experimenting with various ways of creating singletons in F#, so that I understand the subtleties better. I don't know if the singleton pattern is ever useful in F#, but I wanted to experiment. And I was surprised by one result involving static constructors on those singleton instances. First I'll show you my code, and then I'll go into more details about my question. In one project called TrySingleton , I created three modules. Here's Eager.fs : module TrySingleton.Eager type EagerClass

问题 Here http://www.parashift.com/c++-faq-lite/multiple-inheritance.html section [25.14] says The very first constructors to be executed are the virtual base classes anywhere in the hierarchy. I tried to verify it using following program: A (pure virtual) | B | C (virtual)/ \ (virtual) E D \ / F | G (pure virtual) | H each class has a c'tor and virtual d'tor. the output is as follows: A B C E D F G H ~H ~G ~F ~D ~E ~C ~B ~A Press any key to continue . . . but as per quote virtual base classes

问题 I defined a new variable in __construct() and I want to use it in another function of this class . But my variable is empty in the other function! this is my code: class testObject{ function __construct() { global $c; $data = array("name"=>$c['name'], "family"=>$c['family']); } function showInfo() { global $data; print_r($data); } } 回答1: Declare variable $data as global inside the constructor: function __construct() { global $c; global $data; $data = array("name"=>$c['name'], "family"=>$c[

问题 As you can see from my nickname I'm newbie actually learning about Singleton pattern, where I got one problem. Before I've learned that static constructors are always executed before the standard constructors, but in this code below, the result is different, first I see the "Insta" string then the "Static", why does it happen ? sealed class Singleton { private static readonly Singleton instance; private Singleton() { Console.WriteLine("Insta"); } static Singleton() { instance = new Singleton(

问题 I've got a small hierarchy of objects that in general gets constructed from data in a Stream , but for some particular subclasses, can be synthesized from a simpler argument list. In chaining the constructors from the subclasses, I'm running into an issue with ensuring the disposal of the synthesized stream that the base class constructor needs. Its not escaped me that the use of IDisposable objects this way is possibly just dirty pool (plz advise?) for reasons I've not considered, but, this

问题 I have some problems understanding when and if the move constructor or move assignment operator are invoked, in particular in the context of a class with constant data member. Consider the class template<typename T> class A { const*T const P ; // constant data member explicit A(const*T p) : P(p) { std::cerr<<" ctor: P="<<P<<'\n'; } void test() const { std::cerr" test: P="<<P<<'\n'; } // move and copy constructors and assignment operators here }; and the test program class B { int X[100]; A<B>

问题 Having a public copy constructor will make the little program compile, but not showing the side effect "Copy". #include <iostream> class X { public: X(int) { std::cout << "Construct" << std::endl; } // Having a public copy constructor will make the little program // compile, but not showing the side effect "Copy". private: X(const X&) { std::cout << "Copy" << std::endl; } private: X& operator = (const X&); }; int main() { X x = 1; return 0; } 回答1: Here are the relevant bits of the C++

问题 I currently have the following code that retrieves data from the database and then create a User . This code is used in many of my classe to create other objects such as News , Comments etc... It uses apache commons dbutils. final ResultSetHandler<User> handler = new ResultSetHandler<User>() { @Override public User handle(ResultSet rs) throws SQLException { User user = null; if (rs.next()) { user = new User(); user.setId(rs.getInt("id")); user.setUsername(rs.getString("username")); user

问题 I have a class with two constructors (C#). Here is the code snippet: public class FooBar() { public FooBar(string s) { // constructor 1, some functionality } public FooBar(int i) : this("My String") { // constructor 2, some other functionality } } Yes, I know that I can call one constructor from another using the above mentioned approach. But in this scenario, if I call constructor 2, all statements in constructor 1 will run BEFORE the very statement in constructor 2 is executed. What I want

问题 In Python 3, I have the following code: class A: def __init__(self): pass class B(A): def __init__(self): super().__init__() This yields the Pylint warning: Old-style class defined. (old-style-class) Use of super on an old style class (super-on-old-class) In my understanding, in Python 3 there does not exist an old-style class anymore and this code is OK. Even if I explicitly use new-style classes with this code class A(object): def __init__(self): pass class B(A): def __init__(self): super()