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  • Constructors with inheritance in c++

    - by Crystal
    If you have 3 classes, with the parent class listed first shape- 2d shapes, 3d shapes - circle, sphere When you write your constructor for the circle class, would you ever just initialize the parent Shape object and then your current object, skipping the middle class. It seems to me you could have x,y coordinates for Shape and initialize those in the constructor, and initialize a radius in the circle or sphere class, but in 2d or 3d shape classes, I wouldn't know what to put in the constructor since it seems like it would be identical to shape. So is something like this valid Circle::Circle(int x, int y, int r) : Shape(x, y), r(r) {} I get a compile error of: illegal member initialization: 'Shape' is not a base or member So I wasn't sure if my code was legal or best practice even. Or if instead you'd have the middle class just do what the top level Shape class does TwoDimensionalShape::TwoDimensionalShape(int x, int y) : Shape (x, y) {} and then in the Circle class Circle::Circle(int x, int y, int r) : TwoDimensionalShape(x, y), r(r) {}

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  • How to map inheritance with property returned other inheritance?

    - by dario-g
    Hi I have abstract class Vehicle and two classes that derive from: Car and ForkLift. public abstract class Vehicle { public EngineBase Engine { get; set; } } public class Car : Vehicle { public GasEngine Engine { get; set; } } public class ForkLift : Vehicle { public ElectricEngine Engine { get; set; } } and Engine clasess: public abstract class Engine { } public class GasEngine : Engine { } public class ElectricEngine : Engine { } Engines are mapped with "table per class hierarchy". With Vehicles I want to use the same pattern. How to map Engine class and derived with that Engine property?

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  • Inheritance policy when designing the base class

    - by Xaqron
    I have a base class and a derived class both in design phase. The base class will remain one but many derived class will inherit from it. So it's very costly to make change to derived classes in the future and I'm looking for the best design to prevent this. In fact derived class only needs a few methods to override (if needed) but it's tempting to reveal more details to it. My question is about the policy which is extensible in future. Can I minimize the inherited methods/properties to derived class and reveal more in the next versions if needed without any change to derived classes ? Or I should reveal anything that maybe used by derived classes in the future and let them to choose if they need them or not ? Thanks

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  • Simultaneous private and public inheritance in C++

    - by gspr
    Suppose a class Y publicly inherits a class X. Is it possible for a class Z to privately inherit Y while publicly inheriting X? To make this clearer, suppose X defines public methods x1 and x2. Y inherits X, overrides x1 and provides a method y. Does C++ allow for a third class Z to subclass Y in such a way that Y's implementation of x1 and y are privately available to it, while the outside world only sees it inheriting X publicly, i.e. having only a single public method x2?

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  • C#, Generic Lists and Inheritance

    - by Andy
    I have a class called Foo that defines a list of objects of type A: class Foo { List<A> Items = new List<A>(); } I have a class called Bar that can save and load lists of objects of type B: class Bar { void Save(List<B> ComplexItems); List<B> Load(); } B is a child of A. Foo, Bar, A and B are in a library and the user can create children of any of the classes. What I would like to do is something like the following: Foo MyFoo = new Foo(); Bar MyBar = new Bar(); MyFoo.Items = MyBar.Load(); MyBar.Save(MyFoo.Items); Obviously this won't work. Is there a clever way to do this that avoids creating intermediate lists? thanks, Andy

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  • C++ allocate objects on heap of base class with protected constructors via inheritance

    - by KRao
    I have a class with protected constructor: class B { protected: B(){}; }; Now I derive from it and define two static functions and I manage to actually create objects of the class B, but not on the heap: class A : public B { public: static B createOnStack() {return B();} //static B* createOnHeap() {return new B;} //Compile time Error on VS2010 }; B b = A::createOnStack(); //This works on VS2010! The question is: 1) Is VS2010 wrong in allowing the first case? 2) Is it possible to create objects of B without modifying B in any way (no friendship and no extra functions). I am asking, because it is possible to make something similar when dealing with instances of B and its member functions, see: http://accu.org/index.php/journals/296 Thank you in advance for any suggestion! Kind regards

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  • defualt parameter values in arguments and inheritance

    - by sil3nt
    Hello there, Im having trouble with some Java, How do I give in default parameter values in java?. for example I have this in c++ DVD(int i, string t, int y, string d="Unknown"): Items(i,t,y),director(d){} and in Java I tried public Dvd(int i, String t,int y, String d="Unknown"){ super(i,t,y); director = d; } which fails to build. So how do I go about giving in default values? also In my main testing class I tried giving in 3 arguments insead of 4 but this fails also. How do I get around this problem?.

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  • Javascript Inheritance and Arrays

    - by Inespe
    Hi all! I am trying to define a javascript class with an array property, and its subclass. The problem is that all instances of the subclass somehow "share" the array property: // class Test function Test() { this.array = []; this.number = 0; } Test.prototype.push = function() { this.array.push('hello'); this.number = 100; } // class Test2 : Test function Test2() { } Test2.prototype = new Test(); var a = new Test2(); a.push(); // push 'hello' into a.array var b = new Test2(); alert(b.number); // b.number is 0 - that's OK alert(b.array); // but b.array is containing 'hello' instead of being empty. why? As you can see I don't have this problem with primitive data types... Any suggestions?

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  • C# Function Inheritance--Use Child Class Vars with Base Class Function

    - by Sean O'Connor
    Good day, I have a fairly simple question to experienced C# programmers. Basically, I would like to have an abstract base class that contains a function that relies on the values of child classes. I have tried code similar to the following, but the compiler complains that SomeVariable is null when SomeFunction() attempts to use it. Base class: public abstract class BaseClass { protected virtual SomeType SomeVariable; public BaseClass() { this.SomeFunction(); } protected void SomeFunction() { //DO SOMETHING WITH SomeVariable } } A child class: public class ChildClass:BaseClass { protected override SomeType SomeVariable=SomeValue; } Now I would expect that when I do: ChildClass CC=new ChildClass(); A new instance of ChildClass should be made and CC would run its inherited SomeFunction using SomeValue. However, this is not what happens. The compiler complains that SomeVariable is null in BaseClass. Is what I want to do even possible in C#? I have used other managed languages that allow me to do such things, so I certain I am just making a simple mistake here. Any help is greatly appreciated, thank you.

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  • Objective C - Custom Getter with inheritance

    - by anhdat
    Recently I have worked with Core Data. When I want to set a default value for some fields, I came up with this problem: So I made a simple represent: We have 2 class Parent and Child, in which Child inherit from Parent. // Parent.h @interface Parent : NSObject @property (strong, nonatomic) NSString *lastName; // Child.h @interface Child : Parent In Parent class, I made a custom getter to set a default value when nothing is set: // Parent.h - (NSString *)lastName { if (_lastName) { return _lastName; } else { return @"Parent Default Name"; } } But I cannot make a custom default value for the field "name" which Child inherits from its Parent. // Child.h @implementation Child - (NSString *)lastname { if (super.lastName) { return super.lastName; } else { return @"Child Default Name"; } } Apparently, this method is never called. So my question here is: How can I set a custom getter for the field the Child class inherits from Parent without define an overriding property?

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  • Pass Variables In Inheritance (Obj - C)

    - by Marmik Shah
    I working on a project in Obj-C where i have a base class (ViewController) and a Derived Class (MultiPlayer). Now i have declared certain variables and properties in the base class. My properties are getting accessed from the derived class but im not able to access the variables (int,char and bool type). I'm completely new to Obj-C so i have no clue whats wrong. I have used the data types which are used in C and C++. Is there some specific way to declare variables in Obj-C?? If so, How? Here are my files ViewController.h #import <UIKit/UIKit.h> @interface ViewController : UIViewController @property (weak,nonatomic) IBOutlet UIImageView* backGroungImage; @property (strong,nonatomic) IBOutlet UIImageView *blockView1; @property (strong,nonatomic) IBOutlet UIImageView *blockView2; @property (strong,nonatomic) IBOutlet UIImageView *blockView3; @property (strong,nonatomic) IBOutlet UIImageView *blockView4; @property (strong,nonatomic) IBOutlet UIImageView *blockView5; @property (strong,nonatomic) IBOutlet UIImageView *blockView6; @property (strong,nonatomic) IBOutlet UIImageView *blockView7; @property (strong,nonatomic) IBOutlet UIImageView *blockView8; @property (strong,nonatomic) IBOutlet UIImageView *blockView9; @property (strong,nonatomic) UIImage *x; @property (strong,nonatomic) UIImage *O; @property (strong,nonatomic) IBOutlet UIImageView* back1; @property (strong,nonatomic) IBOutlet UIImageView* back2; @end ViewController.m #import "ViewController.h" @interface ViewController () @end @implementation ViewController int chooseTheBackground = 0; int movesToDecideXorO = 0; int winningArrayX[3]; int winningArrayO[3]; int blocksTotal[9] = {8,3,4,1,5,9,6,7,2}; int checkIfContentInBlocks[9] = {0,0,0,0,0,0,0,0,0}; char determineContentInBlocks[9] = {' ',' ',' ',' ',' ',' ',' ',' ',' '}; bool player1Win = false; bool player2Win = false; bool playerWin = false; bool computerWin = false; - (void)viewDidLoad { [super viewDidLoad]; if(chooseTheBackground==0) { UIImage* backImage = [UIImage imageNamed:@"MainBack1.png"]; _backGroungImage.image=backImage; } if(chooseTheBackground==1) { UIImage* backImage = [UIImage imageNamed:@"MainBack2.png"]; _backGroungImage.image=backImage; } } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } @end I am not able to use the above declared variables in my derived classes!

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  • C++ Iterators and inheritance

    - by jomnis
    Have a quick question about what would be the best way to implement iterators in the following: Say I have a templated base class 'List' and two subclasses "ListImpl1" and "ListImpl2". The basic requirement of the base class is to be iterable i.e. I can do: for(List<T>::iterator it = list->begin(); it != list->end(); it++){ ... } I also want to allow iterator addition e.g.: for(List<T>::iterator it = list->begin()+5; it != list->end(); it++){ ... } So the problem is that the implementation of the iterator for ListImpl1 will be different to that for ListImpl2. I got around this by using a wrapper ListIterator containing a pointer to a ListIteratorImpl with subclasses ListIteratorImpl2 and ListIteratorImpl2, but it's all getting pretty messy, especially when you need to implement operator+ in the ListIterator. Any thoughts on a better design to get around these issues?

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  • C++ Inheritance and Constructors

    - by DizzyDoo
    Hello, trying to work out how to use constructors with an inherited class. I know this is very much wrong, I've been writing C++ for about three days now, but here's my code anyway: clientData.h, two classes, ClientData extends Entity : #pragma once class Entity { public: int x, y, width, height, leftX, rightX, topY, bottomY; Entity(int x, int y, int width, int height); ~Entity(); }; class ClientData : public Entity { public: ClientData(); ~ClientData(); }; and clientData.cpp, which contains the functions: #include <iostream> #include "clientData.h" using namespace std; Entity::Entity(int x, int y, int width, int height) { this->x = x; this->y = y; this->width = width; this->height = height; this->leftX = x - (width/2); this->rightX = x + (width/2); this->topY = y - (height/2); this-bottomY = y + (height/2); } Entity::~Entity() { cout << "Destructing.\n"; } ClientData::ClientData() { cout << "Client constructed."; } ClientData::~ClientData() { cout << "Destructing.\n"; } and finally, I'm creating a new ClientData with: ClientData * Data = new ClientData(32,32,32,16); Now, I'm not surprised my compiler shouts errors at me, so how do I pass the arguments to the right classes? The first error (from MVC2008) is error C2661: 'ClientData::ClientData' : no overloaded function takes 4 arguments and the second, which pops up whatever changes I seem to make is error C2512: 'Entity' : no appropriate default constructor available Thanks.

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  • Python Attributes and Inheritance

    - by user368186
    Say I have the folowing code: class Class1(object): def __init__(self): self.my_attr = 1 self.my_other_attr = 2 class Class2(Class1): def __init__(self): super(Class1,self).__init__() Why does Class2 not inherit the attributes of Class1?

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  • C++ Inheritance Question

    - by shaz
    I have a base class MessageHandler and 2 derived classes, MessageHandler_CB and MessageHandler_DQ. The derived classes redefine the handleMessage(...) method. MH_DQ processes a message and puts the result in a deque while MH_CB processes the message and then executes a callback function. The base class has a static callback function that I pass along with a this pointer to a library which calls the static callback when a new message is available for processing. My problem comes when I am in the static callback with a void * pointing to either a MH_DQ or a MH_CB. If I cast it to the base class the empty MessageHandler::handleMessage(...) method is called, rather than the version in the appropriate derived class. What is the best way to address this situation from a design perspective and/or what language features might help me to implement a solution to my problem? Thanks in advance!

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  • c++ Multiple Inheritance - Compiler modifying my pointers

    - by Bob
    If I run the following code, I get different addresses printed. Why? class Base1 { int x; }; class Base2 { int y; }; class Derived : public Base1, public Base2 { }; union U { Base2* b; Derived* d; U(Base2* b2) : b(b) {} }; int main() { Derived* d = new Derived; cout << d << "\n"; cout << U(d).d << "\n"; return 0; } Even more fun is if you repeatedly go in and out of the union the address keeps incrementing by 4, like this int main() { Derived* d = new Derived; cout << d << "\n"; d = U(d).d; cout << d << "\n"; d = U(d).d; cout << d << "\n"; return 0; } If the union is modified like this, then the problem goes away union U { void* v; Base2* b; Derived* d; U(void* v) : v(v) {} }; Also, if either base class is made empty, the problem goes away. Is this a compiler bug? I want it to leave my pointers the hell alone.

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  • Javascript: Inherit method from base class and return the subclass's private variable

    - by marisbest2
    I have the following BaseClass defined: function BaseClass (arg1,arg2,arg3) { //constructor code here then - var privateVar = 7500; this.getPrivateVar = function() { return privateVar; }; } I want to have the following subclass which allows changing privateVar like so: function SubClass (arg1,arg2,arg3,privateVar) { //constructor code here then - var privateVar = privateVar; } SubClass.prototype = new BaseClass(); Now I want SubClass to inherit the getPrivateVar method. However, when I try this, it always returns 7500 which is the value in the BaseClass and not the value of privateVar. In other words, is it possible to inherit a BaseClass's public methods but have any references in them refer to the SubClass's properties? And how would I do that?

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  • Java inheritance question

    - by user247866
    So I have 3 classes. Abstract class A Class B extends class A independent Class C In class D that contains the main method, I create a list of instances of class B List<B> b = method-call();` // the method returns a list of instances of class B Now in class C I have one method that is common to both A and B, and hence I don't want to duplicate it. I want to have one method that takes as input an instance of class A, as follows: public void some-method(LIst<A> a) However, when I do: C c = new C(). c. some-method(b) I get an error that some-method is not applicable for the argument List, instead it's expecting to get List. Is there a good way to fix this problem? Many thanks!

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  • (C#) iterate over read-only private collection member

    - by DGH
    I have a class which has two HashSet collections as private members. Other classes in my code would like to be able to iterate over those HashSets and read their contents. I don't want to write a standard getter because another class could still do something like myClass.getHashSet().Clear(); Is there any other way to expose the elements of my HashSets to iteration without exposing the reference to the HashSet itself? I'd love to be able to do this in a way that is compatible with for-each loops.

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  • Accessing "Public" methods from "Private" methods in javascript class

    - by mon4goos
    Is there a way to call "public" javascript functions from "private" ones within a class? Check out the class below: function Class() { this.publicMethod = function() { alert("hello"); } privateMethod = function() { publicMethod(); } this.test = function() { privateMethod(); } } Here is the code I run: var class = new Class(); class.test(); Firebug gives this error: publicMethod is not defined: [Break on this error] publicMethod(); Is there some other way to call publicMethod() within privateMethod() without accessing the global class variable [i.e. class.publicMethod()]?

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  • List of private iPhone APIs?

    - by diego nunes
    . . Hi there, everybody. . . I need to do an app to be distributed ad hoc (it doesn't need to go to the store) but I need to get the information about the "data usage" (gprs/3g traffic). It is available on the system, but there is no official API call to get that info. One app made it through Apple testing (it's called "Download Meter"), though, and I emailed the guys to see if they would share the call, but they were not in that mood. . . Is there any list of private APIs or anything like that? Does anyone have any ideas of how could I get that info? Again: the app doesn't need to go to the store, but I need to install it on stock iPhone (ad hoc will do). . Thanks.

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  • Keeping some files private

    - by user490895
    Hi, I was trying to create a directory of private files that could only be accessed when a user logs in. To do this, I used a folder outside the web directory, and then php to access it, if allowed. Here's an example: function display_movie($file){ printf("<video id='movie' width='960' height='416' controls='controls' onerror='fix()'> <source src='movie.php?file=%s' type='video/ogg; codecs=\"theora, vorbis\"'> </video>", rawurlencode($file)); } This works great for images, but breaks the media player. Also, I've only tested this locally on a Linux machine. Any ideas? Thanks.

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  • JScript.NET private variables

    - by Paul Podlipensky
    I'm wondering about JScript.NET private variables. Please take a look on the following code: import System; import System.Windows.Forms; import System.Drawing; var jsPDF = function(){ var state = 0; var beginPage = function(){ state = 2; out('beginPage'); } var out = function(text){ if(state == 2){ var st = 3; } MessageBox.Show(text + ' ' + state); } var addHeader = function(){ out('header'); } return { endDocument: function(){ state = 1; addHeader(); out('endDocument'); }, beginDocument: function(){ beginPage(); } } } var j = new jsPDF(); j.beginDocument(); j.endDocument(); Output: beginPage 2 header 2 endDocument 2 if I run the same script in any browser, the output is: beginPage 2 header 1 endDocument 1 Why it is so?? Thanks, Paul.

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