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• Using a class within another class in asp.net

  - by Phil

  In my site I have class A which selects the required page module (blog,content,gallery etc). I also have class B which provides sqlclient database objects and sql statements. If I use class B in a web form via "Imports Class B". I am able to access the contents. I now would like to use class B within class A but am struggling to find the correct syntax for importing it. Please can someone give me a basic example. We are coming from a classic asp background, and used to simply use includes. We are using VB Thanks.

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• Constructor Overload Problem in C++ Inherrentance

  - by metdos

  Here my code snippet: class Request { public: Request(void); ……….. } Request::Request(void) { qDebug()<<"Request: "<<"Hello World"; } class LoginRequest :public Request { public: LoginRequest(void); LoginRequest(QDomDocument); …………… } LoginRequest::LoginRequest(void) { qDebug()<<"LoginRequest: "<<"Hello World"; requestType=LOGIN; requestId=-1; } LoginRequest::LoginRequest(QDomDocument doc){ qDebug()<<"LoginRequest: "<<"Hello World with QDomDocument"; LoginRequest::LoginRequest(); xmlDoc_=doc; } When call constructor of Overrided LoginRequest LoginRequest *test=new LoginRequest(doc); I came up with this result: Request: Hello World LoginRequest: Hello World with QDomDocument Request: Hello World LoginRequest: Hello World Obviously both constructor of LoginRequest called REquest constructor. Is there any way to cape with this situation? I can construct another function that does the job I want to do and have both constructors call that function. But I wonder is there any solution?

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• How can I reuse a base class function in a derived class

  - by Armen Ablak

  Let's say we have these four classes: BinaryTree, SplayTree (which is a sub-class of BinaryTree), BinaryNode and SplayNode (which is a sub-class of BinaryNode). In class BinaryTree I have 2 Find functions, like this bool Find(const T &) const; virtual Node<T> * Find(const T &, Node<T> *) const; and in SplayTree I would like to reuse the second one, because it works in the same way (for example) as in SplayTree, the only thing different is the return type, which is SplayNode. I thought it might be enough if I use this line in SplayTree.cpp using BinaryTree::Find; but it isn't. So, how can I do this?

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• Python, invoke super constructor

  - by Mike

  class A: def __init__(self): print "world" class B(A): def __init__(self): print "hello" B() hello In all other languages I've worked with the super constructor is invoked implicitly. How does one invoke it in Python? I would expect super(self) but this doesn't work

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• How to use a class's type as the type argument for an inherited collection property in C#

  - by Edelweiss Peimann

  I am trying to create a representation of various types of card that inherit from a generic card class and which all contain references to their owning decks. I tried re-declaring them, as suggested here, but it still won't convert to the specific card type. The code I currently have is as such: public class Deck<T> : List<T> where T : Card { void Shuffle() { throw new NotImplementedException("Shuffle not yet implemented."); } } public class Card { public Deck<Card> OwningDeck { get; set; } } public class FooCard : Card { public Deck<FooCard> OwningDeck { get { return (Deck<FooCard>)base.OwningDeck; } set { OwningDeck = value; } } } The compile-time error I am getting: Error 2 Cannot convert type 'Game.Cards.Deck' to 'Game.Cards.Deck' And a warning suggesting I use a new operator to specify that the hiding is intentional. Would doing so be a violation of convention? Is there a better way? My question to stackoverflow is this: Can what I am trying to do be done elegantly in the .NET type system? If so, can some examples be provided?

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• How do you make a private member in the base class become a public member in the base class?

  - by jasonline

  Consider the following code: class Base { void f() { } }; class Derived: public Base { public: }; What can you change in the derived class, such that you can perform the following: Derived d; d.f(); If the member is declared as public in the base class, adding a using declaration for Base::f in the derived class public section would've fix the problem. But if it is declared as private in the base class, this doesn't seem to work.

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• how do I best create a set of list classes to match my business objects

  - by ken-forslund

  I'm a bit fuzzy on the best way to solve the problem of needing a list for each of my business objects that implements some overridden functions. Here's the setup: I have a baseObject that sets up database, and has its proper Dispose() method All my other business objects inherit from it, and if necessary, override Dispose() Some of these classes also contain arrays (lists) of other objects. So I create a class that holds a List of these. I'm aware I could just use the generic List, but that doesn't let me add extra features like Dispose() so it will loop through and clean up. So if I had objects called User, Project and Schedule, I would create UserList, ProjectList, ScheduleList. In the past, I have simply had these inherit from List< with the appropriate class named and then written the pile of common functions I wanted it to have, like Dispose(). this meant I would verify by hand, that each of these List classes had the same set of methods. Some of these classes had pretty simple versions of these methods that could have been inherited from a base list class. I could write an interface, to force me to ensure that each of my List classes has the same functions, but interfaces don't let me write common base functions that SOME of the lists might override. I had tried to write a baseObjectList that inherited from List, and then make my other Lists inherit from that, but there are issues with that (which is really why I came here). One of which was trying to use the Find() method with a predicate. I've simplified the problem down to just a discussion of Dispose() method on the list that loops through and disposes its contents, but in reality, I have several other common functions that I want all my lists to have. What's the best practice to solve this organizational matter?

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• Scala: Mixing traits with private fields

  - by Vilius Normantas

  It's not much of a question, it's rather my excitement that it's possible at all! I wrote this little example just to prove the opposite - I expected either a compiler error or one of the values (111 or 222, I wasn't sure). scala> trait T1 { private val v = 111; def getValueT1 = v } scala> trait T2 { private val v = 222; def getValueT2 = v } scala> class T12 extends T1 with T2 scala> val t = new T12 scala> t.getValueT1 res9: Int = 111 scala> t.getValueT2 res10: Int = 222 Why doesn't the v get overridden? Off course this works only as long as vs are private, but still.

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• Calling Base Class Functions with Inherited Type

  - by Kein Mitleid

  I can't describe exactly what I want to say but I want to use base class functions with an inherited type. Like I want to declare "Coord3D operator + (Coord3D);" in one class, but if I use it with Vector3D operands, I want it to return Vector3D type instead of Coord3D. With this line of code below, I add two Vector3D's and get a Coord3D in return, as told to me by the typeid().name() function. How do I reorganize my classes so that I get a Vector3D on return? #include <iostream> #include <typeinfo> using namespace std; class Coord3D { public: float x, y, z; Coord3D (float = 0.0f, float = 0.0f, float = 0.0f); Coord3D operator + (Coord3D &); }; Coord3D::Coord3D (float a, float b, float c) { x = a; y = b; z = c; } Coord3D Coord3D::operator+ (Coord3D &param) { Coord3D temp; temp.x = x + param.x; temp.y = y + param.y; temp.z = z + param.z; return temp; } class Vector3D: public Coord3D { public: Vector3D (float a = 0.0f, float b = 0.0f, float c = 0.0f) : Coord3D (a, b, c) {}; }; int main () { Vector3D a (3, 4, 5); Vector3D b (6, 7, 8); cout << typeid(a + b).name(); return 0; }

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• Cant overload python socket.send

  - by ralu

  Code from socket import socket class PolySocket(socket): def __init__(self,*p): print "PolySocket init" socket.__init__(self,*p) def sendall(self,*p): print "PolySocket sendall" return socket.sendall(self,*p) def send(self,*p): print "PolySocket send" return socket.send(self,*p) def connect(self,*p): print "connecting..." socket.connect(self,*p) print "connected" HOST="stackoverflow.com" PORT=80 readbuffer="" s=PolySocket() s.connect((HOST, PORT)) s.send("a") s.sendall("a") Output: PolySocket init connecting... connected PolySocket sendall As we can see, send method is not overloaded.

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• Generics and Derived Classes .NET 3.5

  - by Achilles

  Consider the following where class "Circle" inherits from "Shape": dim objListOfCircles as new List(of Circle) DrawShapes(objListOfCirlces) Private sub DrawShapes(byref objListOfShapes as List(of Shape)) for each objShape as Shape in objListOfShapes objShape.Draw() next end sub I can't get this to work. What is the explaination as to why this doesn't work?

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• Does Qt support virtual pure slots ?

  - by ereOn

  Hi, My GUI project in Qt has a lot of "configuration pages" classes which all inherit directly from QWidget. Recently, I realized that all these classes share 2 commons slots (loadSettings() and saveSettings()). Regarding this, I have two questions: Does it make sense to write a intermediate base abstract class (lets name it BaseConfigurationPage) with these two slots as virtual pure methods ? (Every possible configuration page will always have these two methods, so I would say "yes") Before I do the heavy change in my code (if I have to) : does Qt support virtual pure slots ? Is there anything I should be aware of ? Here is a code example describing everything: class BaseConfigurationPage : public QWidget { // Some constructor and other methods, irrelevant here. public slots: virtual void loadSettings() = 0; virtual void saveSettings() = 0; }; class GeneralConfigurationPage : public BaseConfigurationPage { // Some constructor and other methods, irrelevant here. public slots: void loadSettings(); void saveSettings(); };

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• How can I create activerecord models that are subsets of a certain model?

  - by gsiener

  I've seen this before but can't figure out what the correct term is. Basically, I'd like to create models for a specific subset of table data. E.g. (these are not the real classes) class Person < ActiveRecord::Base class Man < Person <something here> :gender => 'male'

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• C++ superclass constructor calling rules

  - by levik

  What are the C++ rules for calling the superclass constructor from a subclass one?? For example I know in Java, you must do it as the first line of the subclass constructor (and if you don't an implicit call to a no-arg super constructor is assumed - giving you a compile error if that's missing).

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• C#: is there way for a class to 'remove' methods that it has inherited

  - by Craig Johnston

  Is there way for a class to 'remove' methods that it has inherited? eg. If I don't want my class to have a ToString() method can I do something so that it is no longer available?

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• (Cocoa) Can I Subclass and Delegate at the same time?

  - by Alvin

  @interface ClassB <ClassADelegate> : ClassA id <ClassBDelegate> delegate; @end As the code says, ClassB subclasses from ClassA and handles the formation protocol of Class A. However, the variable "delegate" will be duplicated. (ClassA also has "delegate") In fact, it can be done without subclassing, but it seems the code is cumbersome, i.e., to use a variable/function of ClassA, I need to write [[ClassB classA] doSomething] instead of [classB doSomething], where doSomething: is a function of ClassA. Are there any tidy way for me to do that?

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• Java: using generic wildcards with subclassing

  - by gibberish

  Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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• Inheritence and usage of dynamic_cast

  - by Mewzer

  Hello, Suppose I have 3 classes as follows (as this is an example, it will not compile!): class Base { public: Base(){} virtual ~Base(){} virtual void DoSomething() = 0; virtual void DoSomethingElse() = 0; }; class Derived1 { public: Derived1(){} virtual ~Derived1(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD1DoSomething{ ... } }; class Derived2 { public: Derived2(){} virtual ~Derived2(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD2DoSomething{ ... } }; I want to create an instance of Derived1 or Derived2 depending on some setting that is not available until run-time. As I cannot determine the derived type until run-time, then do you think the following is bad practice?... class X { public: .... void GetConfigurationValue() { .... // Get configuration setting, I need a "Derived1" b = new Derived1(); // Now I want to call the special DoSomething for Derived1 (dynamic_cast<Derived1*>(b))->SpecialD1DoSomething(); } private: Base* b; }; I have generally read that usage of dynamic_cast is bad, but as I said, I don't know which type to create until run-time. Please help!

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• .Net Inherited Control Property Default

  - by Yisman

  Hello fellows Im trying to make a simple "ButtonPlus" control. the main idea is to inherit from the button control and add some default property values (such as font,color,padding...) No matter how i try, the WinForm always generates (or "serializes") the property value in the client forms the whole point is to have minimal and clean code, not that every instance of the buttonPlus should have 5 lines of init code. I want that the form designer should not generate any code for theses properties and be able to control them from the ButtonPlus code. In other words, if I change the ForeColor from red to blue only 1 single bingle line of code in the app should change. heres my code so far. as you can see, ive tried using defaultvalue, reset , shouldserialize.... anything i was able to find on the web! Public Class ButtonPlus Inherits Button Sub New() 'AutoSize = True AutoSizeMode = Windows.Forms.AutoSizeMode.GrowAndShrink Font = New System.Drawing.Font("Arial", 11.0!, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, CType(177, Byte)) Padding = New System.Windows.Forms.Padding(3) Anchor = AnchorStyles.Left + AnchorStyles.Right + AnchorStyles.Top ForeColor = Color.Aqua End Sub ' _ 'Public Overrides Property AutoSize() As Boolean ' Get ' Return MyBase.AutoSize ' End Get ' Set(ByVal value As Boolean) ' MyBase.AutoSize = value ' End Set 'End Property Public Function ShouldSerializeAutoSize() As Boolean Return False ' Not AutoSize = True End Function Public Function ShouldSerializeForeColor() As Boolean Return False 'Not ForeColor = Color.Aqua End Function Public Overrides Sub ResetForeColor() ForeColor = Color.Aqua End Sub End Class Thank you very much for taking the time to look this over and answer all the best

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• PHP: How to Pass child class __construct() arguments to parent::__construct() ?

  - by none

  I have a class in PHP like so: class ParentClass { function __construct($arg) { // Initialize a/some variable(s) based on $arg } } It has a child class, as such: class ChildClass extends ParentClass { function __construct($arg) { // Let the parent handle construction. parent::__construct($arg); } } What if, for some reason, the ParentClass needs to change to take more than one optional argument, which I would like my Child class to provide "just in case"? Unless I re-code the ChildClass, it will only ever take the one argument to the constructor, and will only ever pass that one argument. Is this so rare or such a bad practice that the usual case is that a ChildClass wouldn't need to be inheriting from a ParentClass that takes different arguments? Essentially, I've seen in Python where you can pass a potentially unknown number of arguments to a function via somefunction(*args) where 'args' is an array/iterable of some kind. Does something like this exist in PHP? Or should I refactor these classes before proceeding?

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• Doing things with objects as if they were parents

  - by General Ackbar

  Sorry that this is probably a super noob question. But the following code give me an error saying that there are invalid arguments in my call of doStuffToLines(segments) shouldnt I be able to do this since I have my DimensionLineSegment inherits from Lines? private void doStuff() { List<DimensionLineSegment> segments = new List<DimensionLineSegment>(); doStuffToLines(segments); } private void doStuffToLines(List<Line> lines) { }

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• Is it possible to specify a return type of "Derivative(of T)" for a MustOverride sub in VB.NET?

  - by Casey

  VB.NET 2008 .NET 3.5 I have two base classes that are MustInherit (partial). Let's call one class OrderBase and the other OrderItemBase. A specific type of order and order item would inherit from these classes. Let's call these WebOrder (inherits from OrderBase) and WebOrderItem (inherits from OrderItemBase). Now, in the grand scheme of things WebOrder is a composite class containing a WebOrderItem, like so: Public Class WebOrder Inherits OrderBase Public Property OrderItem() as WebOrderItem End Property End Class Public Class WebOrderItem Inherits OrderItemBase End Class In order to make sure any class that derives from OrderBase has the OrderItem property, I would like to do something like this in the OrderBase class: Public MustInherit Class OrderBase Public MustOverride Property OrderItem() as Derivative(Of OrderItemBase) End Class In other words, I want the derived class to be forced to contain a property that returns a derivative of OrderItemBase. Is this possible, or should I be using an entirely different approach?

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• A general declaration for all inherited classes

  - by Soham

  Consider, there is a class called SuperClass from which, ClassA, ClassB, ClassC is derived. From each one of those derived Classes, there are further more two classes are derived each called ChildClassAA and ChildClassAB[AB stands for Bth Child class from the Ath Class.Lets not really pull our hair on this nomenclature]. Now, ideally, I want to declare a general type as a private member of another Class say IndependentClass which can be initialized during run time as either of the objects of type ClassAor ClassB or ClassC and even the derived classes like ClassAA or ClassAB. Is there a possible way to do it?

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• How to override the attr_protected?

  - by KandadaBoggu

  I have STI implementation as follows: class Automobile < ActiveRecord::Base end class Car < Automobile end class Truck < Automobile end class User < ActiveRecord::Base has_many :automobiles accepts_nested_attributes_for :automobiles end I am creating a list of automobiles for a user. For each automobile, the UI sets the type field and the properties associated with the automobile.While form submission, the type field is ignored as it is a protected attribute. How do I work around this issue? Is there a declarative way to unprotect a protected attribute?

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• In Java, is it possible for a super constructor invocation actually invoke a constructor in the calling class?

  - by John Assymptoth

  Super constructor invocation definition: [Primary.] [NonWildTypeArguments] super ( ArgumentListopt ) ; A super constructor call can be prefixed by an Primary expression. Example (taken from JLS): class Outer { class Inner{ } } class ChildOfInner extends Outer.Inner { ChildOfInner() { (new Outer()).super(); // (new Outer()) is the Primary } } Does a Primary expression exist that makes the call to super() the invocation of a constructor of the calling class? Or Java prevents that?

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