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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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  • 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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  • 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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  • Me As Child Type In General Function

    - by Steven
    I have a MustInherit Parent class with two Child classes which Inherit from the Parent. How can I use (or Cast) Me in a Parent function as the the child type of that instance? EDIT: My actual goal is to be able to serialize (BinaryFormatter.Serialize(Stream, Object)) either of my child classes. However, "repeating the code" in each child "seems" wrong. EDIT2: This is my Serialize function. Where should I implement this function? Copying and pasting to each child doesn't seem right, but casting the parent to a child doesn't seem right either. Public Function Serialize() As Byte() Dim bFmt As New BinaryFormatter() Dim mStr As New MemoryStream() bFmt.Serialize(mStr, Me) Return mStr.ToArray() End Function

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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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  • XSD: xs:sequence & xs:choice combination for xs:extension elements of a common base type?

    - by bguiz
    Hi, My question is about defining an XML schema that will validate the following XML: <rules> <other>...</other> <bool>...</bool> <other>...</other> <string>...</string> <other>...</other> </rules> The order of the child nodes does not matter. The cardinality of the child nodes is 0..unbounded. All the child elements of the rules node have a common base type, rule, like so: <xs:complexType name="booleanRule"> <xs:complexContent> <xs:extension base="rule"> ... </xs:extension> </xs:complexContent> </xs:complexType> <xs:complexType name="stringFilterRule"> <xs:complexContent> <xs:extension base="filterRule"> ... </xs:extension> </xs:complexContent> </xs:complexType> My current (feeble) attempt at defining the schema for the rules node is below. However, Can I nest xs:choice within xs:sequence? If, where do I specify the maxOccurs="unbounded" attribute? Is there a better way to do this, such as an xs:sequence which specifies only the base type of its child elements? <xs:element name="rules"> <xs:complexType> <xs:sequence> <xs:choice> <xs:element name="bool" type="booleanRule" /> <xs:element name="string" type="stringRule" /> <xs:element name="other" type="someOtherRule" /> </xs:choice> </xs:sequence> </xs:complexType> </xs:element>

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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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  • ActiveRecord Validations for Models with has_many, belongs_to associations and STI

    - by keruilin
    I have four models: User Award Badge GameWeek The associations are as follows: User has many awards. Award belongs to user. Badge has many awards. Award belongs to badge. User has many game_weeks. GameWeek belongs to user. GameWeek has many awards. Award belongs to game_week. Thus, user_id, badge_id and game_week_id are foreign keys in awards table. Badge implements an STI model. Let's just say it has the following subclasses: BadgeA and BadgeB. Some rules to note: The game_week_id fk can be nil for BadgeA, but can't be nil for BadgeB. Here are my questions: For BadgeA, how do I write a validation that it can only be awarded one time? That is, the user can't have more than one -- ever. For BadgeB, how do I write a validation that it can only be awarded one time per game week?

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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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  • 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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  • django access to parent

    - by SledgehammerPL
    model: class Product(models.Model): name = models.CharField(max_length = 128) (...) def __unicode__(self): return self.name class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Product, through='ReceiptComponent') def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive And now I'd like to get list of the most often useable products: ReceiptComponent.objects.values('product').annotate(Count('product')).order_by('-product__count' the example result: [{'product': 3, 'product__count': 5}, {'product': 6, 'product__count': 4}, {'product': 5, 'product__count': 3}, {'product': 7, 'product__count': 2}, {'product': 1, 'product__count': 2}, {'product': 11, 'product__count': 1}, {'product': 8, 'product__count': 1}, {'product': 4, 'product__count': 1}, {'product': 9, 'product__count': 1}] It's almost what I need. But I'd prefer having Product object not product value, because I'd like to use this in views.py for generating list.

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  • Problem overridding virtual function

    - by William
    Okay, I'm writing a game that has a vector of a pairent class (enemy) that s going to be filled with children classes (goomba, koopa, boss1) and I need to make it so when I call update it calls the childclasses respective update. I have managed to create a example of my problem. #include <stdio.h> class A{ public: virtual void print(){printf("Hello from A");} }; class B : public A{ public: void print(){printf("Hello from B");} }; int main(){ A ab = B(); ab.print(); while(true){} } Output wanted: "Hello from B" Output got: "Hello from A" How do I get it to call B's print function?

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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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  • 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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  • How to change position of inherited items in an Inherited user control

    - by Yalda
    I have used a user control as a base class (let's call it BaseUC) with 3 labels (in 3 lines) on it (they are set as protected). And there is another user control that inherits from it (InheritedUC). I have added two more labels in InheritedUC, which are positioned between the base's labels (so there are 5 lines). Everything is fine is Visiual Studio's design UI view. But when I run the application, labels on BaseUC overlap with the ones in InheritedUC and I can't see the ones on the inherited control. Any ideas to fix this? Thank you very much

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  • Is it possible to override a property and return a derived type in VB.NET?

    - by Casey
    Consider the following classes representing an Ordering system: Public Class OrderBase Public MustOverride Property OrderItem() as OrderItemBase End Class Public Class OrderItemBase End Class Now, suppose we want to extend these classes to a more specific set of order classes, keeping the aggregate nature of OrderBase: Public Class WebOrder Inherits OrderBase Public Overrides Property OrderItem() as WebOrderItem End Property End Class Public Class WebOrderItem Inherits OrderItemBase End Class The Overriden property in the WebOrder class will cause an error stating that the return type is different from that defined in OrderBase... however, the return type is a subclass of the type defined in OrderBase. Why won't VB allow this?

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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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  • 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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  • 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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  • Javascript inherance and use of super: is this possible?

    - by Totty
    var Parent = function(value){ this.value = value; this.value1 = 3; this.hello = function(text){ alert(this.value1 + text); } } var Child = extends(Parent, function(value){ this.value1 = 1; this.hello = function(text){ this.super.hello(text); alert('Child' + this.value1 + this.value); } }) var child = new Child(2); child.hello('ola'); // this must output 2 alerts: // 1: "1ola" // 2: "Child1ola"

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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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  • 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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  • (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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  • 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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