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• why the class of subclass is superclass

  - by Raj

  def singleton_class class << self self end end end class Human proc = lambda { puts 'proc says my class is ' + self.name.to_s } singleton_class.instance_eval do define_method(:lab) do proc.call end end end class Developer < Human end Human.lab # class is Human Developer.lab # class is Human ; oops Why Developer.lab is reporting that it is Human ?

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• Mapping One-to-One subclass in Fluent NHibernate

  - by Mike C.

  I have the following database structure: Event table Id - Guid (PK) Name - NVarChar Description - NVarChar SpecialEvent table Id - Guid (PK) StartDate - DateTime EndDate - DateTime I have an abstract Event class, and a SpecialEvent class that inherits from it. Eventually I will have a RecurringEvent class which will inherit from the Event class also. I'd like to map the SpecialEvent class while preserving a one-to-one relationship mapped with the Ids, if possible. Can anybody point me in the correct direction? Thanks!

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• Should I create subclass NSManagedObject or not?

  - by TP

  Hi, I have spent a few days learning and writing NSCoding and finally got it working. However, it took very long to archive and unarchive the (quite complex) object graph, which is unacceptable. After searching the internet for some time, I think the better way is to use core data. Do you recommend that 1) I should rewrite all my classes as subclasses of NSManagedObject or 2) should I create an instance variable of NSManagedObject in each of my class so that any changes to the class also updates its core data representation? Doing either way will need significant changes to the exiting classes and I think I have to update lots of unit test cases as well if it changes the way the classes are initialized. What do you recommend? I really don't want to head to the wrong approach again... Thanks!

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• Instance_eval: why the class of subclass is superclass

  - by Raj

  def singleton_class class << self self end end class Human proc = lambda { puts 'proc says my class is ' + self.name.to_s } singleton_class.instance_eval do define_method(:lab) do proc.call end end end class Developer < Human end Human.lab # class is Human Developer.lab # class is Human ; oops Following solution works. def singleton_class class << self self end end class Human proc = lambda { puts 'proc says my class is ' + self.name.to_s } singleton_class.instance_eval do define_method(:lab) do self.instance_eval &proc end end end class Developer < Human end Human.lab # class is Human Developer.lab # class is Human ; oops Why Developer.lab is reporting that it is Human ? And what can be done so that proc reports Developer when Developer.lab is invoked.

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• Double-click an NSImageCell subclass

  - by Michael Forrest

  I have a table of draggable rows. I'm subclassing NSImageCell to render an image, mapped via bindings. How do I get a double-click event from this cell?

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• abstract class need acces to subclass atribute

  - by user1742980

  I have a problem with my code. public abstract class SimplePolygon implements Polygon { ... public String toString(){ String str = "Polygon: vertices ="; for(int i = 0;i<varray.length;i++){ str += " "; str += varray[i]; } return str; } } public class ArrayPolygon extends SimplePolygon { private Vertex2D[] varray; public ArrayPolygon(Vertex2D[] array){ varray = new Vertex2D[array.length]; if (array == null){} for(int i = 0;i<array.length;i++){ if (array[i] == null){} varray[i] = array[i]; } ... } Problem is, that i'm not allowed to add any atribute or method to abstract class SimplePolygon, so i'cant properly initialize varray. It could simply be solved with protected atrib in that class, but for some (stupid) reason i'cant do that. Has anybody an idea how to solve it without that? Thanks for all help.

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• C++ abstract class template + type-specific subclass = trouble with linker

  - by user333279

  Hi there, The project in question is about different endpoints communicating with each other. An endpoint sends events (beyond the scope of the current problem) and can process incoming events. Each event is represented in a generic object as follows: #pragma interface ... // some includes template<typename T> class Event { public: Event(int senderId, Type type, T payload); // Type is an enum Event(int senderId, Type type, int priority, T payload); virtual ~Event(); virtual int getSenderId(); virtual int getPriority(); virtual T getPayload(); void setPriority(const int priority); protected: const int senderId; const Type type; const T payload; int priority; }; It has its implementing class with #pragma implementation tag. An endpoint is defined as follows: #pragma interface #include "Event.h" template<typename T> class AbstractEndPoint { public: AbstractEndPoint(int id); virtual ~AbstractEndPoint(); virtual int getId(); virtual void processEvent(Event<T> event) = 0; protected: const int id; }; It has its implementing class too, but only the constructor, destructor and getId() are defined. The idea is to create concrete endpoints for each different payload type. Therefore I have different payload objects and specific event classes for each type, e.g. Event<TelegramFormatA>, Event<TelegramFormatB> and ConcreteEndPoint for TelegramFormatA, ConcreteEndPoint for TelegramFormatB respectively. The latter classes are defined as class ConcreteEndPoint : AbstractEndPoint<TelegramFormatA> { ... } I'm using g++ 4.4.3 and ld 2.19. Everything compiles nicely, but the linker complaints about undefined references to type-specific event classes, like Event<TelegramFormatA>::Event(....) . I tried explicit instantiation using template class AbstractEndPoint<TelegramFormatA>; but couldn't get past the aforementioned linker errors. Any ideas would be appreciated.

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• Default subclass objects in Sqlalchemy?

  - by Timmy

  im using the example from the pylons book orm.mapper(Comment, comment_table) orm.mapper(Tag, tag_table) orm.mapper(Nav, nav_table, polymorphic_on=nav_table.c.type, polymorphic_identity='nav') orm.mapper(Section, section_table, inherits=Nav, polymorphic_identity='section') orm.mapper(Page, page_table, inherits=Nav, polymorphic_identity='page', properties={ 'comments':orm.relation(Comment, backref='page', cascade='all'), 'tags':orm.relation(Tag, secondary=pagetag_table) }) i am mostly copying from this, but is there a simple way have a default Page that gets referenced, but if users requests a change, create a new Page object? thanks i want something similar to this class DefaultPage(Page): __init__(self): self.a = a self.b = b self.c = c orm.mapper(DefaultPage, None, inherits=Nav, yada yada )

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• super(type,subclass) in simple singleton implementation

  - by Tianchen Wu

  when I was implementing naive singleton in python, I came up with a problem with super key word. As usual the behavior of super is always tricky and buggy, hope someone can shed light on it. Thanks :) The problem is that: class Singleton(object): def __new__(cls,*args,**kw): if not hasattr(cls,'_instance'): #create a instance of type cls, origin=super(Singleton,Singleton).__new__(cls,*args,**kw) cls._instance=origin return cls._instance class B(Singleton): def __init__(self,b): self.b=b It actually works, but I am wondering Will it be better if I change line 5 to the below, like in most of the books? origin=super(Singleton,cls).__new__(cls,*args,**ks) what's the difference to make?

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• Creating an instance of a subclass extending an abstract class (Java)

  - by dacay

  In Java, is there any way to create an instance of any class that extends abstract class A, inside a member method of class A? Classes that extends abstract class A will return their instances with this method, but i don't want to implement same method in all subclasses with a "return this();" kind line.

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• Objectify - Retrieve subclass instances with superclass query

  - by Deviling Master

  for a project i'm making, i'm using Objectify and Google AppEngine I'm quoting and old message from Google Groups, but the problem i have is the same: Here's the problem I'm trying to solve: I'd like to persist instances of several subclasses of one superclass to the datastore, and then retrieve them by querying for that superclass. (For example, a query for Game would return instances of Chess and Backgammon). Is there any way to accomplish this using Objectify? Because the thing i want is the same, but the topic does not provides yet an answer (it's 3 years old), I moved here with the same question. From 2010 to now, this question has been solved? Thanks Bye

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• Call subclass constructor from abstract class in Java

  - by Joel

  public abstract class Parent { private Parent peer; public Parent() { peer = new ??????("to call overloaded constructor"); } public Parent(String someString) { } } public class Child1 extends parent { } public class Child2 extends parent { } When I construct an instance of Child1, I want a "peer" to automatically be constructed which is also of type Child1, and be stored in the peer property. Likewise for Child2, with a peer of type Child2. The problem is, on the assignment of the peer property in the parent class. I can't construct a new Child class by calling new Child1() because then it wouldn't work for Child2. How can I do this? Is there a keyword that I can use that would refer to the child class? Something like new self()?

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• how to map SubclassMap and HasManyToMany in Fluent NHibernate

  - by Davide Orazio Montersino

  Hi everyone. My problem is fluent nhibernate mapping a many to many relationship, they end up referencing a non existent Id. public UserMap() { Id(x => x.Id); Map(x => x.Name); Map(x => x.Password); Map(x => x.Confirmed); HasMany(x => x.Nodes).Cascade.SaveUpdate(); HasManyToMany<Node>(x => x.Events).Cascade.SaveUpdate().Table("RSVPs"); } public EventMap() { Map(x => x.Starts); Map(x => x.Ends); HasManyToMany<User>(x => x.Rsvps).Cascade.SaveUpdate().Table("RSVPs"); } public NodeMap() { Id(x => x.Id); Map(x => x.Title); Map(x => x.Body).CustomSqlType("text"); Map(x => x.CreationDate); References(x => x.Author).Cascade.SaveUpdate(); Map(x => x.Permalink).Unique().Not.Nullable(); } Those are my classes -notice that Event inherits from Node: public class Event : Node//, IEvent { private DateTime _starts = DateTime.MinValue; private DateTime _ends = DateTime.MaxValue; public virtual IList<User> Rsvps { get; set; } } The problem is, the generated RSVPs table is like that: Event_id User_id Node_id Of course the Event table has no ID - only a Node_id. When trying to save a relationship it will try to save a NULL event_id thus generating an error.

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• C++ How to deep copy a struct with unknown datatype?

  - by Ewald Peters

  hi, i have a "data provider" which stores its output in a struct of a certain type, for instance struct DATA_TYPE1{ std::string data_string; }; then this struct has to be casted into a general datatype, i thought about void * or char *, because the "intermediate" object that copies and stores it in its binary tree should be able to store many different types of such struct data. struct BINARY_TREE_ENTRY{ void * DATA; struct BINARY_TREE_ENTRY * next; }; this void * is then later taken by another object that casts the void * back into the (struct DATA_TYPE1 *) to get the original data. so the sender and the receiver know about the datatype DATA_TYPE1 but not the copying object inbetween. but how can the intermidiate object deep copy the contents of the different structs, when it doesn't know the datatype, only void * and it has no method to copy the real contents; dynamic_cast doesn't work for void *; the "intermediate" object should do something like: void store_data(void * CASTED_DATA_STRUCT){ void * DATA_COPY = create_a_deepcopy_of(CASTED_DATA_STRUCT); push_into_bintree(DATA_COPY); } a simple solution would be that the sending object doesn't delete the sent data struct, til the receiving object got it, but the sending objects are dynamically created and deleted, before the receiver got the data from the intermediate object, for asynchronous communication, therefore i want to copy it. instead of converting it to void * i also tried converting to a superclass pointer of which the intermediate copying object knows about, and which is inherited by all the different datatypes of the structs: struct DATA_BASE_OBJECT{ public: DATA_BASE_OBJECT(){} DATA_BASE_OBJECT(DATA_BASE_OBJECT * old_ptr){ std::cout << "this should be automatically overridden!" << std::endl; } virtual ~DATA_BASE_OBJECT(){} }; struct DATA_TYPE1 : public DATA_BASE_OBJECT { public: string str; DATA_TYPE1(){} ~DATA_TYPE1(){} DATA_TYPE1(DATA_TYPE1 * old_ptr){ str = old_ptr->str; } }; and the corresponding binary tree entry would then be: struct BINARY_TREE_ENTRY{ struct DATA_BASE_OBJECT * DATA; struct BINARY_TREE_ENTRY * next; }; and to then copy the unknown datatype, i tried in the class that just gets the unknown datatype as a struct DATA_BASE_OBJECT * (before it was the void *): void * copy_data(DATA_BASE_OBJECT * data_that_i_get_in_the_sub_struct){ struct DATA_BASE_OBJECT * copy_sub = new DATA_BASE_OBJECT(data_that_i_get_in_the_sub_struct); push_into_bintree(copy_sub); } i then added a copy constructor to the DATA_BASE_OBJECT, but if the struct DATA_TYPE1 is first casted to a DATA_BASE_OBJECT and then copied, the included sub object DATA_TYPE1 is not also copied. i then thought what about finding out the size of the actual object to copy and then just memcopy it, but the bytes are not stored in one row and how do i find out the real size in memory of the struct DATA_TYPE1 which holds a std::string? Which other c++ methods are available to deepcopy an unknown datatype (and to maybe get the datatype information somehow else during runtime) thanks Ewald

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• Java - For a given function foo(X i); in Interface X, why can't implementing class Y change it to fo

  - by incrediman

  For example public interface X{ public void foo(X i); } public class Y implements X{//error: doesn't implement foo(X i)... public void foo(Y i){ fooBar(foo); } .... } Why can't I do that?

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• Java - abstract class, equals(), and two subclasses

  - by msr

  Hello, I have an abstract class named Xpto and two subclasses that extend it named Person and Car. I have also a class named Test with main() and a method foo() that verifies if two persons or cars (or any object of a class that extends Xpto) are equals. Thus, I redefined equals() in both Person and Car classes. Two persons are equal when they have the same name and two cars are equal when they have the same registration. However, when I call foo() in the Test class I always get "false". I understand why: the equals() is not redefined in Xpto abstract class. So... how can I compare two persons or cars (or any object of a class that extends Xpto) in that foo() method? In summary, this is the code I have: public abstract class Xpto { } public class Person extends Xpto{ protected String name; public Person(String name){ this.name = name; } public boolean equals(Person p){ System.out.println("Person equals()?"); return this.name.compareTo(p.name) == 0 ? true : false; } } public class Car extends Xpto{ protected String registration; public Car(String registration){ this.registration = registration; } public boolean equals(Car car){ System.out.println("Car equals()?"); return this.registration.compareTo(car.registration) == 0 ? true : false; } } public class Teste { public static void foo(Xpto xpto1, Xpto xpto2){ if(xpto1.equals(xpto2)) System.out.println("xpto1.equals(xpto2) -> true"); else System.out.println("xpto1.equals(xpto2) -> false"); } public static void main(String argv[]){ Car c1 = new Car("ABC"); Car c2 = new Car("DEF"); Person p1 = new Person("Manel"); Person p2 = new Person("Manel"); foo(p1,p2); } }

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• "Subclassing" show in Haskell?

  - by me2

  Lets say I have the following: data Greek = Alpha | Beta | Gamma | Phi deriving Show I want to use the default showing of all items except Beta, which I want to say "two". Can I do this?

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• Adding custom methods to a subclassed NSManagedObject

  - by CJ

  I have a Core Data model where I have an entity A, which is an abstract. Entities B, C, and D inherit from entity A. There are several properties defined in entity A which are used by B, C, and D. I would like to leverage this inheritance in my model code. In addition to properties, I am wondering if I can add methods to entity A, which are implemented in it's sub-entities. For example: I add a method to the interface for entity A which returns a value and takes one argument I add implementations of this method to A, B, C, D Then, I call executeFetchRequest: to retrieve all instances of B I call the method on the objects retrieved, which should call the implementation of the method contained in B's implementation I have tried this, but when calling the method, I receive: [NSManagedObject methodName:]: unrecognized selector sent to instance I presume this is because the objects returned by executeFetchRequest: are proxy objects of some sort. Is there any way to leverage inheritance using subclassed NSManagedObjects? I would really like to be able to do this, otherwise my model code would be responsible for determining what type of NSManagedObject it's dealing with and perform special logic according to the type, which is undesirable. Any help is appreciated, thanks in advance.

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• Methods in super that will be subclassed anyway (Cocoa)

  - by Michael Matheus

  Sorry if this is a repost but I couldn't quite search for it because I can't explain it in a few words. I have a super class with lots of methods but they will always (not all of them) be subclassed. From the super I need to access (read only) those methods. I could either leave the methods in super empty or I could just not type them in super but call them anyway like so [self myMethod] and it will call my subclassed method even if it doesn't exist in super. This works but Xcode gives me an error though. 'superclass' may not respond to '-subclassmethod' What should I do?

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• Using Sub-Types And Return Types in Scala to Process a Generic Object Into a Specific One

  - by pr1001

  I think this is about covariance but I'm weak on the topic... I have a generic Event class used for things like database persistance, let's say like this: class Event( subject: Long, verb: String, directobject: Option[Long], indirectobject: Option[Long], timestamp: Long) { def getSubject = subject def getVerb = verb def getDirectObject = directobject def getIndirectObject = indirectobject def getTimestamp = timestamp } However, I have lots of different event verbs and I want to use pattern matching and such with these different event types, so I will create some corresponding case classes: trait EventCC case class Login(user: Long, timestamp: Long) extends EventCC case class Follow( follower: Long, followee: Long, timestamp: Long ) extends EventCC Now, the question is, how can I easily convert generic Events to the specific case classes. This is my first stab at it: def event2CC[T <: EventCC](event: Event): T = event.getVerb match { case "login" => Login(event.getSubject, event.getTimestamp) case "follow" => Follow( event.getSubject, event.getDirectObject.getOrElse(0), event.getTimestamp ) // ... } Unfortunately, this is wrong. <console>:11: error: type mismatch; found : Login required: T case "login" => Login(event.getSubject, event.getTimestamp) ^ <console>:12: error: type mismatch; found : Follow required: T case "follow" => Follow(event.getSubject, event.getDirectObject.getOrElse(0), event.getTimestamp) Could someone with greater type-fu than me explain if, 1) if what I want to do is possible (or reasonable, for that matter), and 2) if so, how to fix event2CC. Thanks!

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• Do I need to override the writing methods of NSDocument in subclasses for an application that will o

  - by Abizern

  I think I may be missing the obvious but I'm not sure. The section on subclassing NSDocument in the docs states that subclasses of NSDocument must override one reading and one writing method. If I'm creating a viewer application that will not write anything back, do I still need to override a writing method (returning what, nil?) or can I ignore it and make sure that there are no saving methods that can get called?

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• Subclassing UIButton but can't access my properties

  - by Ross Ellerington

  Hi, I've created a sub class of UIButton: // // DetailButton.h #import <Foundation/Foundation.h> #import <MapKit/MapKit.h> @interface MyDetailButton : UIButton { NSObject *annotation; } @property (nonatomic, retain) NSObject *annotation; @end // // DetailButton.m // #import "MyDetailButton.h" @implementation MyDetailButton @synthesize annotation; @end I figured that I can then create this object and set the annotation object by doing the following: MyDetailButton* rightButton = [MyDetailButton buttonWithType:UIButtonTypeDetailDisclosure]; rightButton.annotation = localAnnotation; localAnnotation is an NSObject but it is really an MKAnnotation. I can't see why this doesn't work but at runtime I get this error: 2010-05-27 10:37:29.214 DonorMapProto1[5241:207] *** -[UIButton annotation]: unrecognized selector sent to instance 0x445a190 2010-05-27 10:37:29.215 DonorMapProto1[5241:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UIButton annotation]: unrecognized selector sent to instance 0x445a190' ' I can't see why it's even looking at UIButton because I've subclassed that so it should be looking at the MyDetailButton class to set that annotation property. Have I missed something really obvious. It feels like it :) Thanks in advance for any help you can provide Ross

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• Use Automapper to flatten sub-class of property

  - by Neil

  Given the classes: public class Person { public string Name { get; set; } } public class Student : Person { public int StudentId { get; set; } } public class Source { public Person Person { get; set; } } public class Dest { public string PersonName { get; set; } public int? PersonStudentId { get; set; } } I want to use Automapper to map Source - Dest. This test obviously fails: Mapper.CreateMap<Source, Dest>(); var source = new Source() { Person = new Student(){ Name = "J", StudentId = 5 }}; var dest = Mapper.Map<Source, Dest>(source); Assert.AreEqual(5, dest.PersonStudentId); What would be the best approach to mapping this given that "Person" is actually a heavily used data-type throughout our domain model.

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• ASP.NET/C#: How to use a Subclassed Control on a Page?

  - by Bob Kaufman

  I've subclassed DropDownList to add functionality specific to my application: public class MyDropDownList : DropDownList { ... } ... then referenced it in Web.Config, which is where I figure things start to go wrong: <pages theme="Main"> <controls> <add tagPrefix="bob" tagName="MyDropDownList" src="~/Components/MyDropDownList.cs" /> </controls> </pages> my reference to it does not work: <tr><td>Category</td> <td><bob:MyDropDownList runat="server" ID="Category"... /> and my best clue is the complier error message: "The file 'src' is not a valid [sic] here because it doesn't expose a type." I figure I'm misapplying knowledge of how to create a Web User Control here. What I want to be able to do is refer to this control on an ASP.NET page just like I would the parent DropDownList. Refactoring back into a Web User Control that contains a DropDownList is not desirable, because I want to apply a RequiredFieldValidator to it.

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• Making a circular NSSlide look and behave like in GarageBand

  - by Koning Baard

  I am new to drawing with Cocoa, and I am making some software which will have sliders similar to these found in GarageBand: These look beautiful and can be controld by moving the mouse up and down. Can you help me with customizing NSSliders by subclassing them, so I can make them look and behave exactly as in GarageBand? Thanks. I have one image for the knob which should be rotated as they do not need to be in 3D .

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