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• C2664 when casting child class to templated parent class

  - by DC

  I have a parent class which is templated, and a child class which implements it. template< typename T1, typename T2> class ParentClass{ . . . }; class ChildClass : public ParentClass<MyT1, MyT2> { . . . }; And I want to have a pointer which I can use polymorphically: ParentClass<T1, T2>* ptr; ptr = static_cast<ParentClass<MyT1, MyT2>* >(new ChildClass() ); No matter how I cast it, I always get a C2664 which has the same expression: error C2664: cannot convert parameter 1 from 'ParentClass< T1,T2 *' to 'ParentClass< T1,T2 *' Is it not possible to cast pointer types between inherited types if the parent is templated, even if the types specified in the templates are the same?

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• Which design pattern is most appropriate?

  - by Anon

  Hello, I want to create a class that can use one of four algorithms (and the algorithm to use is only known at run-time). I was thinking that the Strategy design pattern sounds appropriate, but my problem is that each algorithm requires slightly different parameters. Would it be a bad design to use strategy, but pass in the relevant parameters into the constructor?. Here is an example (for simplicity, let's say there are only two possible algorithms) ... class Foo { private: // At run-time the correct algorithm is used, e.g. a = new Algorithm1(1); AlgorithmInterface* a; }; class AlgorithmInterface { public: virtual void DoSomething = 0; }; class Algorithm1 : public AlgorithmInterface { public: Algorithm1( int i ) : value(i) {} virtual void DoSomething(){ // Does something with int value }; int value; }; class Algorithm2 : public AlgorithmInterface { public: Algorithm2( bool b ) : value(b) {} virtual void DoSomething(){ // Do something with bool value }; bool value; };

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• Nhibernate - getting single column from other table

  - by Muhammad Akhtar

  I have following tables Employee: ID,CompanyID,Name //CompanyID is foriegn key of Company Table Company: CompanyID, Name I want to map this to the following class: public class Employee { public virtual Int ID { get; set; } public virtual Int CompanyID { get; set; } public virtual string Name { get; set; } public virtual string CompanyName { get; set; } protected Employee() { } } here is my xml class <class name="Employee" table="Employee" lazy="true"> <id name="Id" type="Int32" column="Id"> <generator class="native" /> </id> <property name="CompanyID" column="CompanyID" type="Int32" not-null="false"/> <property name="Name" column="Name" type="String" length="100" not-null="false"/> What I need to add in xml class to map CompanyName in my result? here is my code... public ArrayList getTest() { ISession session = NHibernateHelper.GetCurrentSession(); string query = "select Employee.*,(Company.Name)CompanyName from Employee inner join Employee on Employee.CompanyID = Company.CompanyID"; ArrayList document = (ArrayList)session.CreateSQLQuery(query, "Employee", typeof(Document)).List(); return document; } but in the returned result, I am getting CompanyName is null is result set and other columns are fine. Note:In DB, tables don't physical relation Please suggest my solution ------ Thanks

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• Abstract base class puzzle

  - by 0x80

  In my class design I ran into the following problem: class MyData { int foo; }; class AbstraktA { public: virtual void A() = 0; }; class AbstraktB : public AbstraktA { public: virtual void B() = 0; }; template<class T> class ImplA : public AbstraktA { public: void A(){ cout << "ImplA A()"; } }; class ImplB : public ImplA<MyData>, public AbstraktB { public: void B(){ cout << "ImplB B()"; } }; void TestAbstrakt() { AbstraktB *b = (AbstraktB *) new ImplB; b->A(); b->B(); }; The problem with the code above is that the compiler will complain that AbstraktA::A() is not defined. Interface A is shared by multiple objects. But the implementation of A is dependent on the template argument. Interface B is the seen by the outside world, and needs to be abstrakt. The reason I would like this is that it would allow me to define object C like this: Define the interface C inheriting from abstrakt A. Define the implementation of C using a different datatype for template A. I hope I'm clear. Is there any way to do this, or do I need to rethink my design?

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• EF 4.0 Code only assocation from abstract to derived

  - by Jeroen

  Using EF 4.0 Code only i want to make an assocation between an abstract and normal class. I have class 'Item', 'ContentBase' and 'Test'. 'ContentBase' is abstract and 'Test' derives from it. 'ContentBase' has a property 'Item' that links to an instance of 'Item'. So that 'Test.Item' or any class that derives from 'ContentBase' has an 'Item' navigation property. In my DB every record for Test has a matching record for Item. public class Item { public int Id { get; set;} } public abstract class ContentBase { public int ContentId { get; set;} public int Id { get; set;} public Item Item { get; set;} } public class Test : ContentBase { public string Name { get; set;} } now some init code public void SomeInitFunction() { var itemConfig = new EntityConfiguration<Item>(); itemConfig.HasKey(p => p.Id); itemConfig.Property(p => p.Id).IsIdentity(); this.ContextBuilder.Configurations.Add(itemConfig); var testConfig = new EntityConfiguration<Test>(); testConfig.HasKey(p => p.ContentId); testConfig.Property(p => p.ContentId).IsIdentity(); // the problem testConfig.Relationship(p => p.Item).HasConstraint((p, q) => p.Id == q.Id); this.ContextBuilder.Configurations.Add(testConfig); } This gives an error: A key is registered for the derived type 'Test'. Keys must be registered for the root type 'ContentBase'. anyway i try i get an error. What am i a doing wrong?

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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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• 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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• 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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• 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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• Seam @Factory in abstract base class?

  - by Shadowman

  I've got a series of web actions I'm implementing in Seam to perform create, read, update, etc. operations. For my read/update/delete actions, I'd like to have individual action classes that all extend an abstract base class. I'd like to put the @Factory method in the abstract base class to retrieve the item that is to be acted upon. For example, I have this as the base class: public abstract class BaseAction { @In(required=false)@Out(required=false) private MyItem item=null; public MyItem getItem(){...} public void setItem(...){...} @Factory("item") public void initItem(){...} } My subclasses would extend BaseAction, so that I don't have to repeat the logic to load the item that is to be viewed, deleted, updated, etc. However, when I start my application, Seam throws errors saying I have declared multiple @Factory's for the same object. Is there any way around this? Is there any way to provide the @Factory in the base class without encoutnering these errors?

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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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• Generic version control strategy for select table data within a heavily normalized database

  - by leppie

  Hi Sorry for the long winded title, but the requirement/problem is rather specific. With reference to the following sample (but very simplified) structure (in psuedo SQL), I hope to explain it a bit better. TABLE StructureName { Id GUID PK, Name varchar(50) NOT NULL } TABLE Structure { Id GUID PK, ParentId GUID (FK to Structure), NameId GUID (FK to StructureName) NOT NULL } TABLE Something { Id GUID PK, RootStructureId GUID (FK to Structure) NOT NULL } As one can see, Structure is a simple tree structure (not worried about ordering of children for the problem). StructureName is a simplification of a translation system. Finally 'Something' is simply something referencing the tree's root structure. This is just one of many tables that need to be versioned, but this one serves as a good example for most cases. There is a requirement to version to any changes to the name and/or the tree 'layout' of the Structure table. Previous versions should always be available. There seems to be a few possibilities to tackle this issue, like copying the entire structure, but most approaches causes one to 'loose' referential integrity. Example if one followed this approach, one would have to make a duplicate of the 'Something' record, given that the root structure will be a new record, and have a new ID. Other avenues of possible solutions are looking into how Wiki's handle this or go a lot further and look how proper version control systems work. Currently, I feel a bit clueless how to proceed on this in a generic way. Any ideas will be greatly appreciated. Thanks leppie

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• SRP & "axis of change"?

  - by lance

  I'm reading Bob Martin's principles of OOD, specifically the SRP text, and I understand the spirit of what it's saying pretty well, but I don't quite understand a particular phrasing, from page 2 of the link (page 150 of the book): I paraphrase: It is important to separate these two responsibilities into separate classes because each responsibility is an axis of change. What exactly is meant here by "axis of change"?

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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 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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• Getting the last User ID in Zend Framework

  - by Ryan Murphy

  Using MySQL query browser, I manually made a table called users and input some date in the fields. I set the primary key to id and set it to auto increment. There are 3 rows, the highest id is 3. I then made the following class in the method directory to call upon the data in the table etc. class Application_Model_DbTable_User extends Zend_Db_Table_Abstract { protected $_name = 'user'; public function getLatestUserId() { $id = $this->getAdapter()->lastInsertId(); return $id; } } In the controller I do the following which gets the value generated by the method and lets the view access it: $usersDbModel = new Application_Model_DbTable_User(); $lastUserId = $usersDbModel->getLatestUserId(); $this->view->lastUserId = $lastUserId; In the view I then echo it to display it to the user: echo $this->lastUserId; However, even though my last id in the users table is 3. It displays 0. I have also tried: public function getLatestUserId() { $sql = 'SELECT max(id) FROM user'; $query = $this->query($sql); $result = $query->fetchAll(); return $result; } But this just throws out a server error. What have I done wrong? Am I missing something? Is there another way of doing 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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• 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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• 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 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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• To OpenID or not to OpenID? Is it worth it?

  - by Eloff

  Does OpenID improve the user experience? Edit Not to detract from the other comments, but I got one really good reply below that outlined 3 advantages of OpenID in a rational bottom line kind of way. I've also heard some whisperings in other comments that you can get access to some details on the user through OpenID (name? email? what?) and that using that it might even be able to simplify the registration process by not needing to gather as much information. Things that definitely need to be gathered in a checkout process: Full name Email (I'm pretty sure I'll have to ask for these myself) Billing address Shipping address Credit card info There may be a few other things that are interesting from a marketing point of view, but I wouldn't ask the user to manually enter anything not absolutely required during the checkout process. So what's possible in this regard? /Edit (You may have noticed stackoverflow uses OpenID) It seems to me it is easier and faster for the user to simply enter a username and password in a signup form they have to go through anyway. I mean you don't avoid entering a username and password either with OpenID. But you avoid the confusion of choosing a OpenID provider, and the trip out to and back from and external site. With Microsoft making Live ID an OpenID provider (More Info), bringing on several hundred million additional accounts to those provided by Google, Yahoo, and others, this question is more important than ever. I have to require new customers to sign up during the checkout process, and it is absolutely critical that the experience be as easy and smooth as possible, every little bit harder it becomes translates into lost sales. No geek factor outweighs cold hard cash at the end of the day :) OpenID seems like a nice idea, but the implementation is of questionable value. What are the advantages of OpenID and is it really worth it in my scenario described above?

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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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• 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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