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• AS3 Memory management when instantiating extended classes

  - by araid

  I'm developing an AS3 application which has some memory leaks I can't find, so I'd like to ask some newbie questions about memory management. Imagine I have a class named BaseClass, and some classes that extend this one, such as ClassA, ClassB, etc. I declare a variable: myBaseClass:BaseClass = new ClassA(); After a while, I use it to instantiate a new object: myBaseClass = new ClassB(); some time after myBaseClass = new ClassC(); and the same thing keeps happening every x millis, triggered by a timer. Is there any memory problem here? Are the unused instances correctly deleted by the garbage collector? Thanks!

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• A question about entities, roles and interfaces in Entity Framework 4.

  - by mvole

  Hi, I am an experienced .NET developer but new to EF - so please bear with me. I will use an example of a college application to illustrate my problem. I have these user roles: Lecturer, Student, Administrator. In my code I envisage working with these entities as distinct classes so e.g. a Lecturer teaches a collection of Students. And work with 'is Student' 'TypeOf' etc. Each of these entities share lots of common properties/methods e.g. they can all log onto the system and do stuff related to their role. In EF designer I can create a base entity Person (or User...) and have Lecturer, Student and Administrator all inherit from that. The difficulty I have is that a Lecturer can be an Administrator - and in fact on occasion a Student can be a Lecturer. If I were to add other entities such as Employee and Warden then this gets even more of an issue. I could presumably work with Interfaces so a person could implement ILecturer and IStudent, however I do not see how this fits within EF. I would like to work within the EF designer if possible and I'm working model-first (coding in C#). So any help and advice/samples would be very welcome and much appreciated. Thanks

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• Different return value of an overridden class

  - by Samer Afach

  I have a simple but confusing question here. Is it legal to have a different return value type for overridden methods than the abstact ones defined in the base class?? I did that and the compiler didn't complain... could someone please explain? class MyBaseClass { int value; public: virtual int getValue() = 0; }; class MyClass : public MyBaseClass { double value; public: virtual double getValue(); // here!!! return is double, not int }; double MyClass::getValue() { return this->value; } The compiler totally accepted something similar (MSVC und MinGW)... could anyone please exaplain to what extent this is legal?

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• Why am I getting this error when overriding an inherited method?

  - by Sergio Tapia

  Here's my parent class: public abstract class BaseFile { public string Name { get; set; } public string FileType { get; set; } public long Size { get; set; } public DateTime CreationDate { get; set; } public DateTime ModificationDate { get; set; } public abstract void GetFileInformation(); public abstract void GetThumbnail(); } And here's the class that's inheriting it: public class Picture:BaseFile { public override void GetFileInformation(string filePath) { FileInfo fileInformation = new FileInfo(filePath); if (fileInformation.Exists) { Name = fileInformation.Name; FileType = fileInformation.Extension; Size = fileInformation.Length; CreationDate = fileInformation.CreationTime; ModificationDate = fileInformation.LastWriteTime; } } public override void GetThumbnail() { } } I thought when a method was overridden, I could do what I wanted with it. Any help please? :)

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• C++ function overloading and dynamic binding compile problem

  - by Olorin

  #include <iostream> using namespace std; class A { public: virtual void foo(void) const { cout << "A::foo(void)" << endl; } virtual void foo(int i) const { cout << i << endl; } virtual ~A() {} }; class B : public A { public: void foo(int i) const { this->foo(); cout << i << endl; } }; class C : public B { public: void foo(void) const { cout << "C::foo(void)" << endl; } }; int main(int argc, char ** argv) { C test; test.foo(45); return 0; } The above code does not compile with: $>g++ test.cpp -o test.exe test.cpp: In member function 'virtual void B::foo(int) const': test.cpp:17: error: no matching function for call to 'B::foo() const' test.cpp:17: note: candidates are: virtual void B::foo(int) const test.cpp: In function 'int main(int, char**)': test.cpp:31: error: no matching function for call to 'C::foo(int)' test.cpp:23: note: candidates are: virtual void C::foo() const It compiles if method "foo(void)" is changed to "goo(void)". Why is this so? Is it possible to compile the code without changing the method name of "foo(void)"? Thanks.

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• Question of using static_cast on "this" pointer in a derived object to base class

  - by Johnyy

  Hi, this is an example taken from Effective C++ 3ed, it says that if the static_cast is used this way, the base part of the object is copied, and the call is invoked from that part. I wanted to understand what is happening under the hood, will anyone help? class Window { // base class public: virtual void onResize() { } // base onResize impl }; class SpecialWindow: public Window { // derived class public: virtual void onResize() { // derived onResize impl; static_cast<Window>(*this).onResize(); // cast *this to Window, // then call its onResize; // this doesn't work! // do SpecialWindow- } // specific stuff };

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• Interface(s) inheriting other interface(s) in WCF services.

  - by avance70

  In my solution there's a few WCF services, each of them implementing it's own callback interface. Let's say they are called: Subscribe1, with ISubscribe1 and ICallback1, etc. It happens there are a few methods shared among ICallbacks, so I made a following interface: interface ICallback { [OperationContract] CommonlyUsedMethod(); } and i inherited it in all: ICallback1 : ICallback, ICallback2 : ICallback, etc. And deleted the CommonlyUsedMethod() from all callback interfaces. Now, on the service-side code, everything compiles fine and services can start working as usual. But, when I updated the service references for the client, CommonlyUsedMethod() dissapeared from the reference.cs file (the ISubscribeCallback part), and could no longer be used to send data to back to the client.

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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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• Rails 3 Abstract Class vs Inherited Class

  - by R. Yanchuleff

  In my rails 3 model, I have two classes: Product, Service. I want both to be of type InventoryItem because I have another model called Store and Store has_many :InventoryItems This is what I'm trying to get to, but I'm not sure how to model this in my InventoryItem model and my Product and Service models. Should InventoryItem just be a parent class that Product and Service inherit from, or should InventoryItem be modeled as a class abstract of which Product and Service extend from. Thanks in advance for the advice!

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• PHP: Extending static member arrays

  - by tstenner

  I'm having the following scenario: class A { public static $arr=array(1,2); } class B extends A { public static $arr=array(3,4); } Is there any way to combine these 2 arrays so B::$arr is 1,2,3,4? I don't need to alter these arrays, but I can't declare them als const, as PHP doesn't allow const arrays.http://stackoverflow.com/questions/ask The PHP manual states, that I can only assign strings and constants, so parent::$arr + array(1,2) won't work, but I think it should be possible to do this.

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• C++ overloading virtual = operator

  - by taz

  Hello, here is the code for my question: class ICommon { public: virtual ICommon& operator=(const ICommon & p)const=0; }; class CSpecial : public ICommon { public: CSpecial& operator=(const CSpecial & cs) { //custom operations return *this; } }; CSpecial obj; Basically: I want the interface ICommon to force it's descendants to implement = operator but don't want to have any typecasts in the implementation. The compiler says "can't instantiate an abstract class. Any help/advice will be appreciated.

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• Java method get the inheriting type

  - by DrDro

  I have several classes that extend C and I would need a method that accepts any argument of type C. But in this method I would like to know if I'm dealing with A or B. * public A extends C public B extends C public void goForIt(C c)() If I cast how can I retrieve the type in a clean way (I just read using getClass or instanceof is often not the best way). PS: Fell free to edit an explicit title. *Sorry but I can't type closing braces

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• How to find out the subclass from the base class object

  - by Vaishak Suresh

  Is there a way to find out the derived class's name from a base class object? ex: class A{ .... } class B extends A{ ... } class c extends A{ ... } now if a method returns an object of A, can I find out if it is of type B or C?

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• How are declared private ivars different from synthesized ivars?

  - by lemnar

  I know that the modern Objective-C runtime can synthesize ivars. I thought that synthesized ivars behaved exactly like declared ivars that are marked @private, but they don't. As a result, come code compiles only under the modern runtime that I expected would work on either. For example, a superclass: @interface A : NSObject { #if !__OBJC2__ @private NSString *_c; #endif } @property (nonatomic, copy) NSString *d; @end @implementation A @synthesize d=_c; - (void)dealloc { [_c release]; [super dealloc]; } @end and a subclass: @interface B : A { #if !__OBJC2__ @private NSString *_c; #endif } @property (nonatomic, copy) NSString *e; @end @implementation B @synthesize e=_c; - (void)dealloc { [_c release]; [super dealloc]; } @end A subclass can't have a declared ivar with the same name as one of its superclass's declared ivars, even if the superclass's ivar is private. This seems to me like a violation of the meaning of @private, since the subclass is affected by the superclass's choice of something private. What I'm more concerned about, however, is how should I think about synthesized ivars. I thought they acted like declared private ivars, but without the fragile base class problem. Maybe that's right, and I just don't understand the fragile base class problem. Why does the above code compile only in the modern runtime? Does the fragile base class problem exist when all superclass instance variables are private?

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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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• How to determine which inheriting class is using an abstract class's methods.

  - by Kin

  In my console application have an abstract Factory class "Listener" which contains code for listening and accepting connections, and spawning client classes. This class is inherited by two more classes (WorldListener, and MasterListener) that contain more protocol specific overrides and functions. I also have a helper class (ConsoleWrapper) which encapsulates and extends System.Console, containing methods for writing to console info on what is happening to instances of the WorldListener and MasterListener. I need a way to determine in the abstract ListenerClass which Inheriting class is calling its methods. Any help with this problem would be greatly appreciated! I am stumped :X Simplified example of what I am trying to do. abstract class Listener { public void DoSomething() { if(inheriting class == WorldListener) ConsoleWrapper.WorldWrite("Did something!"); if(inheriting class == MasterListener) ConsoleWrapper.MasterWrite("Did something!"); } } public static ConsoleWrapper { public void WorldWrite(string input) { System.Console.WriteLine("[World] {0}", input); } } public class WorldListener : Listener { public void DoSomethingSpecific() { ConsoleWrapper.WorldWrite("I did something specific!"); } } public void Main() { new WorldListener(); new MasterListener(); } Expected output [World] Did something! [World] I did something specific! [Master] Did something! [World] I did something specific!

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• Using child visitor in C#

  - by Thomas Matthews

  I am setting up a testing component and trying to keep it generic. I want to use a generic Visitor class, but not sure about using descendant classes. Example: public interface Interface_Test_Case { void execute(); void accept(Interface_Test_Visitor v); } public interface Interface_Test_Visitor { void visit(Interface_Test_Case tc); } public interface Interface_Read_Test_Case : Interface_Test_Case { uint read_value(); } public class USB_Read_Test : Interface_Read_Test_Case { void execute() { Console.WriteLine("Executing USB Read Test Case."); } void accept(Interface_Test_Visitor v) { Console.WriteLine("Accepting visitor."); } uint read_value() { Console.WriteLine("Reading value from USB"); return 0; } } public class USB_Read_Visitor : Interface_Test_Visitor { void visit(Interface_Test_Case tc) { Console.WriteLine("Not supported Test Case."); } void visit(Interface_Read_Test_Case rtc) { Console.WriteLine("Not supported Read Test Case."); } void visit(USB_Read_Test urt) { Console.WriteLine("Yay, visiting USB Read Test case."); } } // Code fragment USB_Read_Test test_case; USB_Read_Visitor visitor; test_case.accept(visitor); What are the rules the C# compiler uses to determine which of the methods in USB_Read_Visitor will be executed by the code fragment? I'm trying to factor out dependencies of my testing component. Unfortunately, my current Visitor class contains visit methods for classes not related to the testing component. Am I trying to achieve the impossible?

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• How do I make a class whose interface matches double, but upon which templates can be specialized?

  - by Neil G

  How do I make a class whose interface matches double, but whose templated types do not dynamic cast to double? The reason is that I have a run-time type system, and I want to be able to have a type that works just like double: template<int min_value, int max_value> class BoundedDouble: public double {}; And then inherit use template specialization to get run-time information about that type: template<typename T> class Type { etc. } template<int min_value, int max_value> class Type<BoundedDouble<min_value, max_value>> { int min() const { return min_value; } etc. } But, you can't inherit from double...

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• How to enforce users to create objects of class derived from mine with "new" only?

  - by sharptooth

  To implement reference counting we use an IUnknown-like interface and a smart pointer template class. The interface has implementation for all the reference-count methods, including Release(): void IUnknownLike::Release() { if( --refCount == 0 ) { delete this; } } The smart pointer template class has a copy constructor and an assignment operator both accepting raw pointers. So users can do the following: class Class : public IUnknownLike { }; void someFunction( CSmartPointer<Class> object ); //whatever function Class object; someFunction( &object ); and the program runs into undefined behavior - the object is created with reference count zero, the smart pointer is constructed and bumps it to one, then the function returns, smart pointer is destroyed, calls Release() which leads to delete of a stack-allocated variable. Users can as well do the following: struct COuter { //whatever else; Class inner;// IUnknownLike descendant }; COuter object; somefunction( &object.Inner ); and again an object not created with new is deleted. Undefined behavior at its best. Is there any way to change the IUnknownLike interface so that the user is forced to use new for creating all objects derived from IUnknownLike - both directly derived and indirectly derived (with classes in between the most derived and the base)?

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• Cannot inherit from generic base class and specific interface using same type with generic constrain

  - by simendsjo

  Sorry about the strange title. I really have no idea how to express it any better... I get an error on the following snippet. I use the class Dummy everywhere. Doesn't the compiler understand the constraint I've added on DummyImplBase? Is this a compiler bug as it works if I use Dummy directly instead of setting it as a constraint? Error 1 'ConsoleApplication53.DummyImplBase' does not implement interface member 'ConsoleApplication53.IRequired.RequiredMethod()'. 'ConsoleApplication53.RequiredBase.RequiredMethod()' cannot implement 'ConsoleApplication53.IRequired.RequiredMethod()' because it does not have the matching return type of 'ConsoleApplication53.Dummy'. C:\Documents and Settings\simen\My Documents\Visual Studio 2008\Projects\ConsoleApplication53\ConsoleApplication53\Program.cs 37 27 ConsoleApplication53 public class Dummy { } public interface IRequired<T> { T RequiredMethod(); } public interface IDummyRequired : IRequired<Dummy> { void OtherMethod(); } public class RequiredBase<T> : IRequired<T> { public T RequiredMethod() { return default(T); } } public abstract class DummyImplBase<T> : RequiredBase<T>, IDummyRequired where T: Dummy { public void OtherMethod() { } }

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• PyQt - QLabel inheriting

  - by Ockonal

  Hello, i wanna inherit QLabel to add there click event processing. I'm trying this code: class NewLabel(QtGui.QLabel): def __init__(self, parent): QtGui.QLabel.__init__(self, parent) def clickEvent(self, event): print 'Label clicked!' But after clicking I have no line 'Label clicked!' EDIT: Okay, now I'm using not 'clickEvent' but 'mousePressEvent'. And I still have a question. How can i know what exactly label was clicked? For example, i have 2 edit box and 2 labels. Labels content are pixmaps. So there aren't any text in labels, so i can't discern difference between labels. How can i do that? EDIT2: I made this code: class NewLabel(QtGui.QLabel): def __init__(self, firstLabel): QtGui.QLabel.__init__(self, firstLabel) def mousePressEvent(self, event): print 'Clicked' #myLabel = self.sender() # None =) self.emit(QtCore.SIGNAL('clicked()'), "Label pressed") In another class: self.FirstLang = NewLabel(Form) QtCore.QObject.connect(self.FirstLang, QtCore.SIGNAL('clicked()'), self.labelPressed) Slot in the same class: def labelPressed(self): print 'in labelPressed' print self.sender() But there isn't sender object in self. What i did wrong?

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• C++: Create abstract class with abstract method and override the method in a subclass

  - by Martijn Courteaux

  Hi, How to create in C++ an abstract class with some abstract methods that I want to override in a subclass? How should the .h file look? Is there a .cpp, if so how should it look? In Java it would look like this: abstract class GameObject { public abstract void update(); public abstract void paint(Graphics g); } class Player extends GameObject { @Override public void update() { // ... } @Override public void paint(Graphics g) { // ... } } // In my game loop: for (int i = 0; i < objects.size(); i++) { objects.get(i).update(); } for (int i = 0; i < objects.size(); i++) { objects.get(i).paint(g); } Translating this code to C++ is enough for me.

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• Why can't I *override* and *new* a Property (C#) at the same time?

  - by Tim Lovell-Smith

  According to this question it seems like you can do this for Methods. What I want to know is why it doesn't work when I try it with properties. public class Foo { public virtual object Value { get; set; } } public class Foo<T> : Foo { public override object Value { get { return base.Value; } set { base.Value = (T)value; //inject type-checking on sets } } public new T Value { get { return (T)base.Value; } set { base.Value = value; } } } Error message from C# 4.0 RC1 Error 1 The type 'ClassLibrary1.Foo' already contains a definition for 'Value' ClassLibrary1\Class1.cs 31 22 ClassLibrary1

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• How to override inner class methods if the inner class is defined as a property of the top class

  - by Maddy

  I have a code snippet like this class A(object): class b: def print_hello(self): print "Hello world" b = property(b) And I want to override the inner class b (please dont worry about the lowercase name) behaviour. Say, I want to add a new method or I want to change an existing method, like: class C(A): class b(A.b): def print_hello(self): print "Inner Class: Hello world" b = property(b) Now if I create C's object as c = C(), and call c.b I get TypeError: 'property' object is not callable error. How would I get pass this and call print_hello of the extended inner class? Disclaimer: I dont want to change the code for A class.

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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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