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  • Liskov substitution principle with abstract parent class

    - by Songo
    Does Liskov substitution principle apply to inheritance hierarchies where the parent is an abstract class the same way if the parent is a concrete class? The Wikipedia page list several conditions that have to be met before a hierarchy is deemed to be correct. However, I have read in a blog post that one way to make things easier to conform to LSP is to use abstract parent instead of a concrete class. How does the choice of the parent type (abstract vs concrete) impacts the LSP? Is it better to have an abstract base class whenever possible?

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  • A question on nature of generated assembly in C++ and code Algebra

    - by Reetesh Mukul
    I wrote this code: #include <iostream> int main() { int a; std::cin >> a; if(a*a== 3){ std::cout << a; } return 0; } On MSVC I turned ON all optimization flags. I expected that since a*a can never be 3, so compiler should not generate code for the section: if(a*a== 3){ std::cout << a; } However it generated code for the section. I did not check GCC or LLVM/CLang. What are the limits of expectation from a C++ compiler in these scenarios?

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  • Why does PHP 5.2 disallow abstract static class methods?

    - by Artem Russakovskii
    After enabling strict warnings in PHP 5.2, I saw a load of strict standards warnings from a project that was originally written without strict warnings: Strict Standards: Static function Program::getSelectSQL() should not be abstract in Program.class.inc The function in question belongs to an abstract parent class Program and is declared abstract static because it should be implemented in its child classes, such as TVProgram. I did find references to this change here: Dropped abstract static class functions. Due to an oversight, PHP 5.0.x and 5.1.x allowed abstract static functions in classes. As of PHP 5.2.x, only interfaces can have them. My question is: can someone explain in a clear way why there shouldn't be an abstract static function in PHP?

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  • protected abstract override Foo(); &ndash; er... what?

    - by Muljadi Budiman
    A couple of weeks back, a co-worker was pondering a situation he was facing.  He was looking at the following class hierarchy: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { } class FirstConcrete : SecondaryBase { } class SecondConcrete : SecondaryBase { } Basically, the first 2 classes are abstract classes, but the OriginalBase class has Test implemented as a virtual method.  What he needed was to force concrete class implementations to provide a proper body for the Test method, but he can’t do mark the method as abstract since it is already implemented in the OriginalBase class. One way to solve this is to hide the original implementation and then force further derived classes to properly implemented another method that will replace it.  The code will look like the following: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { protected sealed override void Test() { Test2(); } protected abstract void Test2(); } class FirstConcrete : SecondaryBase { // Have to override Test2 here } class SecondConcrete : SecondaryBase { // Have to override Test2 here } With the above code, SecondaryBase class will seal the Test method so it can no longer be overridden.  Then it also made an abstract method Test2 available, which will force the concrete classes to override and provide the proper implementation.  Calling Test will properly call the proper Test2 implementation in each respective concrete classes. I was wondering if there’s a way to tell the compiler to treat the Test method in SecondaryBase as abstract, and apparently you can, by combining the abstract and override keywords.  The code looks like the following: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { protected abstract override void Test(); } class FirstConcrete : SecondaryBase { // Have to override Test here } class SecondConcrete : SecondaryBase { // Have to override Test here } The method signature makes it look a bit funky, because most people will treat the override keyword to mean you then need to provide the implementation as well, but the effect is exactly as we desired.  The concepts are still valid: you’re overriding the Test method from its original implementation in the OriginalBase class, but you don’t want to implement it, rather you want to classes that derive from SecondaryBase to provide the proper implementation, so you also make it as an abstract method. I don’t think I’ve ever seen this before in the wild, so it was pretty neat to find that the compiler does support this case.

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  • Ruby Abstract Class Design

    - by MattDiPasquale
    I'm creating a video game. It has Characters & Items. Since I want Characters & Items to each have a name, should I make another class called NamedObjects with just a name field and have Characters & Items extend that? Or is that going overboard?

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  • Abstract Factory Using Generics: Is Explicitly Converting a Specified Type to Generic a Bad Practice

    - by Merritt
    The question's title says it all. I like how it fits into the rest of my code, but does it smell? public interface IFoo<T> { T Bar { get; set; } } public class StringFoo : IFoo<string> { public string Bar { get; set; } } public static class FooFactory { public static IFoo<T> CreateFoo<T>() { if (typeof(T) == typeof(string)) { return new StringFoo() as IFoo<T>; } throw new NotImplementedException(); } } UPDATE: this is sort of a duplicate of Is the StaticFactory in codecampserver a well known pattern?

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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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  • My abstract class implements an interface but doesn't implement some of its methods. How do I make i

    - by Stefan Monov
    interface ICanvasTool { void Motion(Point newLocation); void Tick(); } abstract class CanvasTool_BaseDraw : ICanvasTool { protected abstract void PaintAt(Point location); public override void Motion(Point newLocation) { // implementation } } class CanvasTool_Spray : CanvasTool_BaseDraw { protected abstract void PaintAt(Point location) { // implementation } public override void Tick() { // implementation } } This doesn't compile. I could add an abstract method "Tick_Implementation" to CanvasTool_BaseDraw, then implement ICanvasTool.Tick in CanvasTool_BaseDraw with a one-liner that just calls Tick_Implementation. Is this the recommended workaround?

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  • Interfaces on an abstract class

    - by insta
    My coworker and I have different opinions on the relationship between base classes and interfaces. I'm of the belief that a class should not implement an interface unless that class can be used when an implementation of the interface is required. In other words, I like to see code like this: interface IFooWorker { void Work(); } abstract class BaseWorker { ... base class behaviors ... public abstract void Work() { } protected string CleanData(string data) { ... } } class DbWorker : BaseWorker, IFooWorker { public void Work() { Repository.AddCleanData(base.CleanData(UI.GetDirtyData())); } } The DbWorker is what gets the IFooWorker interface, because it is an instantiatable implementation of the interface. It completely fulfills the contract. My coworker prefers the nearly identical: interface IFooWorker { void Work(); } abstract class BaseWorker : IFooWorker { ... base class behaviors ... public abstract void Work() { } protected string CleanData(string data) { ... } } class DbWorker : BaseWorker { public void Work() { Repository.AddCleanData(base.CleanData(UI.GetDirtyData())); } } Where the base class gets the interface, and by virtue of this all inheritors of the base class are of that interface as well. This bugs me but I can't come up with concrete reasons why, outside of "the base class cannot stand on its own as an implementation of the interface". What are the pros & cons of his method vs. mine, and why should one be used over another?

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  • Why should a class be anything other than "abstract" or "final/sealed"

    - by Nicolas Repiquet
    After 10+ years of java/c# programming, I find myself creating either: abstract classes: contract not meant to be instantiated as-is. final/sealed classes: implementation not meant to serve as base class to something else. I can't think of any situation where a simple "class" (i.e. neither abstract nor final/sealed) would be "wise programming". Why should a class be anything other than "abstract" or "final/sealed" ? EDIT This great article explains my concerns far better than I can.

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  • Difference between Factory Method and Abstract Factory design patterns using C#.Net

    - by nijhawan.saurabh
    First of all I'll just put both these patterns in context and describe their intent as in the GOF book: Factory Method: Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.   Abstract Factory: Provide an interface for creating families of related or dependent objects without specifying their concrete classes.   Points to note:   Abstract factory pattern adds a layer of abstraction to the factory method pattern. The type of factory is not known to the client at compile time, this information is passed to the client at runtime (How it is passed is again dependent on the system, you may store this information in configuration files and the client can read it on execution). While implementing Abstract factory pattern, the factory classes can have multiple factory methods. In Abstract factory, a factory is capable of creating more than one type of product (Simpilar products are grouped together in a factory)   Sample implementation of factory method pattern   Let's see the class diagram first:                   ProductFactory.cs // ----------------------------------------------------------------------- // <copyright file="ProductFactory.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public abstract class ProductFactory     {         /// <summary>         /// </summary>         /// <returns>         /// </returns>         public abstract Product CreateProductInstance();     } }     ProductAFactory.cs // ----------------------------------------------------------------------- // <copyright file="ProductAFactory.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductAFactory:ProductFactory     {         public override Product CreateProductInstance()         {             return new ProductA();         }     } }         // ----------------------------------------------------------------------- // <copyright file="ProductBFactory.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductBFactory:ProductFactory     {         public override Product CreateProductInstance()         {             return new ProductB();           }     } }     // ----------------------------------------------------------------------- // <copyright file="Product.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public abstract class Product     {         public abstract string Name { get; set; }     } }     // ----------------------------------------------------------------------- // <copyright file="ProductA.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductA:Product     {         public ProductA()         {               Name = "ProductA";         }           public override string Name { get; set; }     } }       // ----------------------------------------------------------------------- // <copyright file="ProductB.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductB:Product     {          public ProductB()         {               Name = "ProductA";         }         public override string Name { get; set; }     } }     Program.cs using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace FactoryMethod {     class Program     {         static void Main(string[] args)         {             ProductFactory pf = new ProductAFactory();               Product product = pf.CreateProductInstance();             Console.WriteLine(product.Name);         }     } }       Normal 0 false false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

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  • Desktop Fun: Abstract Icon Packs

    - by Asian Angel
    Do you prefer a more unique, artistic, or alternative look for your desktop setup? Then you will definitely want to have a look through our Abstract Icon Packs collection. Just set your imagination loose and enjoy the wonderful desktops that these icon packs can inspire for you. Note: To customize the icon setup on your Windows 7 & Vista systems see our article here. Using Windows XP? We have you covered here. Sneak Preview For this week’s preview desktop we created an Alien Desert Planet theme using the Abstract Symbol Icons pack shown below. Note: The original, unmodified version of this wallpaper can be found here. Here is a closer look at the icons we used for our new theme… The Icon Packs Match-stick-play Icons *.ico format only Download Abstract Symbol Icons *.ico format only Download Allomantic Metals *.ico format only Download Mutated Snowflake Icon Set *.ico format only Download Shades of Geometry *.ico format only Download Starry Objects Icons *.ico format only Download New Sin – Abstract Human Icons *.ico, .png, and .psd format Note: While most of the icons in this pack look similar at first glance, there are differences when viewed at a larger size. Download Mysterious Icons *.ico format only Download Alien Icons *.ico format only Download Beads Icons *.ico format only Download Magic Flowers Icons *.ico format only Download Circle Shapes Icons *.ico format only Download geometric doc icons *.png format only Download alumina *.png format only Download Citiscape dockicons *.png format only Download Wanting more great icon sets to look through? Be certain to visit our Desktop Fun section for more icon goodness! Latest Features How-To Geek ETC How to Use the Avira Rescue CD to Clean Your Infected PC The Complete List of iPad Tips, Tricks, and Tutorials Is Your Desktop Printer More Expensive Than Printing Services? 20 OS X Keyboard Shortcuts You Might Not Know HTG Explains: Which Linux File System Should You Choose? HTG Explains: Why Does Photo Paper Improve Print Quality? Add Falling Snow to Webpages with the Snowfall Extension for Opera [Browser Fun] Automatically Keep Up With the Latest Releases from Mozilla Labs in Firefox 4.0 A Look Back at 2010 Through Infographics Monitor the Weather with the Weather Forecast Extension for Opera Orbiting at the Edge of the Atmosphere Wallpaper Simon’s Cat Explores the Christmas Tree! [Video]

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  • How can I implement an abstract singleton class in Java?

    - by Simon
    Here is my sample abstract singleton class: public abstract class A { protected static A instance; public static A getInstance() { return instance; } //...rest of my abstract methods... } And here is the concrete implementation: public class B extends A { private B() { } static { instance = new B(); } //...implementations of my abstract methods... } Unfortunately I can't get the static code in class B to execute, so the instance variable never gets set. I have tried this: Class c = B.class; A.getInstance() - returns null; and this ClassLoader.getSystemClassLoader().loadClass("B"); A.getInstance() - return null; Running both these in the eclipse debugger the static code never gets executed. The only way I could find to get the static code executed is to change the accessibility on B's constructor to public, and to call it. I'm using sun-java6-jre on Ubuntu 32bit to run these tests.

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  • How can I create object in abstract class without having knowledge of implementation?

    - by Greg
    Hi, Is there a way to implement the "CreateNode" method in my library abstract below? Or can this only be done in client code outside the library? I current get the error "Cannot create an instance of the abstract class or interface 'ToplogyLibrary.AbstractNode" public abstract class AbstractTopology<T> { // Properties public Dictionary<T, AbstractNode<T>> Nodes { get; private set; } public List<AbstractRelationship<T>> Relationships { get; private set; } // Constructors protected AbstractTopology() { Nodes = new Dictionary<T, AbstractNode<T>>(); } // Methods public AbstractNode<T> CreateNode() { var node = new AbstractNode<T>(); // ** Does not work ** Nodes.Add(node.Key, node); } } } public abstract class AbstractNode<T> { public T Key { get; set; } } public abstract class AbstractRelationship<T> { public AbstractNode<T> Parent { get; set; } public AbstractNode<T> Child { get; set; } }

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  • Best method of including an abstract in a latex 'book'?

    - by olan
    Hello there. I've been looking for the answer to this question for a while now but can't seem to find it, so I'm hoping someone on here can help me. I'm writing up a thesis in Latex, and really like the \frontmatter, \mainmatter and \backmatter ability when using the "book" environment. However I need to add an abstract and the \begin{abstract} environment is undefined when creating a "book". If I change to a "report" however, I lose the functionality of the *matter terms. So what I really need to know is: is there a simple method of including an abstract in a "book" and have it formatted the same as it would be in a "report"? (i.e. centered vertically and horizontally with an 'abstract' heading) Thanks for any help! First post on stackoverflow after reading for months!

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  • linear algebra libraries for clusters

    - by Abruzzo Forte e Gentile
    Hi all I need to develop applications doing linear algebra + eigenvalue + linear equation solutions over a cluster of pcs ( I have a lot of machines available ). I discovered Scalapack libraries but they seem to me developed long time ago. Do you know if these are other libs available that I should learn doing math & linear algebra in a cluster? My language is C++ and off course I am newbie to this topic. Kind Regards to everybody AFG

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  • Can You Have "Empty" Abstract/Classes?

    - by ShrimpCrackers
    Of course you can, I'm just wondering if it's rational to design in such a way. I'm making a breakout clone and was doing some class design. I wanted to use inheritance, even though I don't have to, to apply what I've learned in C++. I was thinking about class design and came up with something like this: GameObject - base class (consists of data members like x and y offsets, and a vector of SDL_Surface* MovableObject : GameObject - abstract class + derived class of GameObject (one method void move() = 0; ) NonMovableObject : GameObject - empty class...no methods or data members other than constructor and destructor(at least for now?). Later I was planning to derive a class from NonMovableObject, like Tileset : NonMovableObject. I was just wondering if "empty" abstract classes or just empty classes are often used...I notice that the way I'm doing this, I'm just creating the class NonMovableObject just for sake of categorization. I know I'm overthinking things just to make a breakout clone, but my focus is less on the game and more on using inheritance and designing some sort of game framework.

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  • Generate Unique Abstract Backgrounds with Ablaze

    - by Jason Fitzpatrick
    If you want custom and unique backgrounds without having to code your own image-generating engine, Ablaze makes it simple (and fun) to create abstract images. You can customize a wide array of options in Ablaze including the base shape (ring, horizontal line, or random), number of particles, distance each particle travels, and the speed (if you increase the speed range you get more distinct lines and if you decrease it you get smoother smokier shapes). You can also seed the design with a color palette pulled from any image you provide (the sample above was seeded with a Wonder Woman comic panel). Tweak and reset the pattern generation as much as you want; when you create an abstract image worthy of your desktop just click the save button to grab a copy of it in PNG format. Ablaze [via Flowing Data] How To Create a Customized Windows 7 Installation Disc With Integrated Updates How to Get Pro Features in Windows Home Versions with Third Party Tools HTG Explains: Is ReadyBoost Worth Using?

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  • Can i override an abstract method written in a parent class, with a different name in a child class?

    - by Ranhiru
    abstract class SettingSaver { public abstract void add(string Name, string Value); public abstract void remove(string SettingName); } class XMLSettings : SettingSaver { public override void add(string Name, string Value) { throw new NotImplementedException(); } public override void remove(string SettingName) { throw new NotImplementedException(); } } Is there anyway that I can change the name of the add function in XMLSettings class to addSetting but make sure it overrides the add function in the SettingSaver? I know it should be definitely overridden in derived classes but just want to know whether I can use a different name :) Thanx in advance :D

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  • Building a database class in PHP

    - by Sprottenwels
    I wonder if I should write a database class for my application, and if so, how to accomplish it? Over there on SO, a guy mentioned it should be written as an abstract class. However, I can't understand why this would be a benefit. Do I understand correctly, that if I would write an abstract class, every other class that methods will need a database connection, could simply extend this abstract class and have it's own database object? If so, how is this different from a "normal" class where I could instantiate an database object? Another method would be to completely forget about my own class and to instantiate a mysqli object on demand. What do you recommend?

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  • What is the better design decision approach?

    - by palm snow
    I have two classes (MyFoo1 and MyFoo2) that share some common functionality. So far it does not seem like I need any polymorphic inheritence but at this point I am considering the following options: Have the common functionality in a utility class. Both of these classes call these methods from that utility class. Have an abstract class and implement common methods in that abstract class. Then derive MyFoo1 and MyFoo2 from that abstract class. Any suggestion on what would be a better design decision?

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