inheritance

Python using derived class's method in parent class?

Can I force a parent class to call a derived class's version of a function? class Base(object): attr1 = '' attr2 = '' def virtual(self): pass # doesn't do anything in the parent class def func(self): print "%s, %s" % (self.attr1, self.attr2) self.virtual() and a class that derive...

Prototypal inheritance: Can you chain Object.create?

I'm new to prototypal inheritance so I'm trying to understand the 'right' way. I thought I could do this: if (typeof Object.create !== 'function') { Object.create = function (o) { function F() {} F.prototype = o; return new F(); }; } var tbase = {}; tbase.Tdata = function Tdata() {}; tbase.Tdata.protot...

Calling the overriden method from the base class in C#

Given the following C# class definitions and code: public class BaseClass { public virtual void MyMethod() { ...do something... } } public class A : BaseClass { public override void MyMethod() { ...do something different... } } public class B : BaseClass { public override void MyMethod() ...

inheritance - how to access a subclass

I am trying to get an author from the BOOK class that extends the Item class. I have 3 classes as follows main() library Item(CD,DVD,Book) inheritance.. in library class i have a function called public Collection booksByAuthor(String author) i also have a hashset in library class that holds information on various books. What i wan...

Should there be 2 datatables for a Parent and Child class in Java?

I have two classes Parent and Child. class Child extends Parent { private String extraField1; private String extraField2; ... } Child class has 2 extra fields extraField1 and extraField2. Q1. Should I make two diff. tables in the databse: one for Child and other for Parent? or Q1. Should I add two columns in the Parent ...

Can a class inherit from LambdaExpression in .NET? Or is this not recommended?

Consider the following code (C# 4.0): public class Foo : LambdaExpression { } This throws the following design-time error: Foo does not implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) There's absolutely no problem with public class Foo : Expression { }...

internal abstract methods. Why would anyone have them ?

I was doing some code review today and came across an old code written by some developer. It goes something like this public abstract class BaseControl { internal abstract void DoSomething(); } If you have a derived class within the same assembly, it would work public class DerivedControl : BaseControl { ...

How can I override a parent class function with child one in Perl?

Hi, I would like to replace parent function (Somefunc) in child class, so when I call Main procedure it should fail. Is it possible in Perl? Code: package Test; use strict; use warnings; sub Main() { SomeFunc() or die "Somefunc returned 0"; } sub SomeFunc() { return 1; } package Test2; use strict; use warnings; our @ISA...

Overwrite data and setData in Qt's QFileSystemModel

Hi, What I'am trying to do: Overwrite QFileSystemModel's setData and data to implement Caching of pictures in the shown directory. I use a QListView for testing purpose. Here is the relevant code: My Class with QFileSystemModel as parent: .h-file: #ifndef QPICSINFILESYSTEMMODEL_H #define QPICSINFILESYSTEMMODEL_H #include <QFileSy...

Constructor in class with inheritance

I'm having some problems with inheritance and constructors in C++. What I've got is a class VirtualMotor which inherits Motor (is that the correct way to say it?). The class VirtualMotor should have it's own constructor, but I'm doing something wrong when I create it and the compiler gives me an error (se below). My source code is like t...

Trying to return various models with Ruby Activescaffold find on models with inheritance

class Promotion def self.get_todays_promotions # Promotion is a parent model, having child models e.g. # DiscountPromotion, VoucherPromotion, etc. # they all use a single table called promotions # (and having 'type' field explaining which model they belong to) promotions = self.find(:all, :conditions => [Promotion....

problem using accept_nested_attributes with polymorphic relations and inheritance

Having this mix of polymorphism and inhertiance, I encounter some weird behaviour: Migration class CreateCommons < ActiveRecord::Migration def self.up create_table :commons do |t| t.string :name t.string :configurable_type t.integer :configurable_id end create_table :specifics do |t| t.integer :nu...

Model inheritance, the Factory pattern, and self-parsing in Ruby-on-Rails

Hi all- I am working with a site that will be pulling down feeds from a lot of different sources, and then saving those streams into a common model, in this case a trait. An example of the code from within the FeedEntry class might be: feed = Feedzirra::Feed.fetch_and_parse(feed_url) add_entries(feed.entries) ... def self.add_entrie...

Can I make interfaces or abstract classes in C# that declare methods with a parameter of unknown type?

I'm parsing a http GET query string into its components. In trying to make it modular (the number and types of parameters can vary quite a bit), I want to have a Parameter abstract base class or interface that defines whether a property has been set or not, along with a Set method that sets the value. Is there a way to do that with a var...

deriving a templated class in c++

I have a templated base class which follows: template<class scalar_type, template<typename > class functor> class convex_opt{ .. }; How to derive a class from this templated class? ...

C# Class Inheritance

greetings. i have the following class: public class Ship { public enum ValidShips { Minesweeper, Cruiser, Destroyer, Submarine, AircraftCarrier } public enum ShipOrientation { North, East, South, West } public enum ShipStatus { ...

Modifying type-specific properties in implementation of interface

I know this is a silly question, in that the answer is likely an "oh right, of course!" one. Here is what I have: public interface IEvent { int Id string Title } public class MeetingEvent : IEvent { int Id string Title //Meeting Properties string Room; User Organizer; } public class BirthdayEvent : IEvent { int Id ...

Persisting non-entity class that extends an entity (jpa) - example?

The JPA tutorial states that one can have a non-entity that extends entity class: Entities may extend both entity and non-entity classes, and non-entity classes may extend entity classes. - http://java.sun.com/javaee/5/docs/tutorial/doc/bnbqa.html Is it possible to persist such structure? I want to do this: @Entity abstract...

SharePoint Content Type Inheritance: Inheriting UI defined CT from a feature

Is it possible to create a Custom content type declaratively using features in 12 hive that inherits from a custom content type that was created through UI. For example, CT-A is created through SharePoint UI, CT-B is a child of CT-A but can I create it using xml. I would create an ID for CT-B as : "Id of CT-A + 00 + GUID" to signify tha...

How can I determine if instance of class from Django model is subclass of another model?

I have a class called BankAccount as base class. I also have CheckingAccount and SavingsAccount classes that inherit from BankAccount. BankAccount is not an abstract class but I do not create an object from it, only the inheriting classes. Then, I execute a query like this: account = BankAccount.objects.get(id=10) How do I know if a...