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  • Visitor-pattern vs inheritance for rendering

    - by akaltar
    I have a game engine that currently uses inheritance to provide a generic interface to do rendering: class renderable { public: void render(); }; Each class calls the gl_* functions itself, this makes the code hard to optimize and hard to implement something like setting the quality of rendering: class sphere : public renderable { public: void render() { glDrawElements(...); } }; I was thinking about implementing a system where I would create a Renderer class that would render my objects: class sphere { void render( renderer* r ) { r->renderme( *this ); } }; class renderer { renderme( sphere& sphere ) { // magically get render resources here // magically render a sphere here } }; My main problem is where should I store the VBOs and where should I Create them when using this method? Should I even use this approach or stick to the current one, perhaps something else? PS: I already asked this question on SO but got no proper answers.

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  • Inheritance of list-style-type property in Firefox (bug in Firebug?)

    - by Marcel Korpel
    Let's have a look at some comments on a page generated by Wordpress (it's not a site I maintain, I'm just wondering what's going on here). As these pages might disappear in the near future, I've put some screenshots online. Here's what I saw: Obviously, the list-item markers shouldn't be there. So I decided to look at the source using Firebug. As you can see, Firebug claims that the list-style property (containing none) is inherited from ol.commentlist. But if that's the case, why are the circle and the square visible? When checking the computed style, Firebug shows the list-style-types correctly. What's the correct behaviour? I just did a quick check in Chromium, whose Web Inspector gave a better view of reality (the list item markers were also displayed in this browser): According to WebKit, list-style of ol.commentlist isn't inherited, only the default value of list-style-type from the rendering engine. So, we may conclude that the output of both browsers is correct and that Firefox (Firebug) shows an incorrect representation of inherited styles. What does the CSS specification say? Inheritance will transfer the list-style values from OL and UL elements to LI elements. This is the recommended way to specify list style information. Not much about the inheritance of ol properties to uls. Is Firebug wrong in this respect? BTW, I managed to let the markers disappear by just changing line 312 of style.css to ol.commentlist, li.commentlist, ul.children { When also explicitly defining the list-style of ul.children to none, the markers are not painted. You can have a look at screenshots of Firebug and WebKit's Web Inspector in this case, if you like.

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  • Inheritance, commands and event sourcing

    - by Arthis
    In order not to redo things several times I wanted to factorize common stuff. For Instance, let's say we have a cow and a horse. The cow produces milk, the horse runs fast, but both eat grass. public class Herbivorous { public void EatGrass(int quantity) { var evt= Build.GrassEaten .WithQuantity(quantity); RaiseEvent(evt); } } public class Horse : Herbivorous { public void RunFast() { var evt= Build.FastRun; RaiseEvent(evt); } } public class Cow: Herbivorous { public void ProduceMilk() { var evt= Build.MilkProduced; RaiseEvent(evt); } } To eat Grass, the command handler should be : public class EatGrassHandler : CommandHandler<EatGrass> { public override CommandValidation Execute(EatGrass cmd) { Contract.Requires<ArgumentNullException>(cmd != null); var herbivorous= EventRepository.GetById<Herbivorous>(cmd.Id); if (herbivorous.IsNull()) throw new AggregateRootInstanceNotFoundException(); herbivorous.EatGrass(cmd.Quantity); EventRepository.Save(herbivorous, cmd.CommitId); } } so far so good. I get a Herbivorous object , I have access to its EatGrass function, whether it is a horse or a cow doesn't matter really. The only problem is here : EventRepository.GetById<Herbivorous>(cmd.Id) Indeed, let's imagine we have a cow that has produced milk during the morning and now wants to eat grass. The EventRepository contains an event MilkProduced, and then come the command EatGrass. With the CommandHandler, we are no longer in the presence of a cow and the herbivorious doesn't know anything about producing milk . what should it do? Ignore the event and continue , thus allowing the inheritance and "general" commands? or throw an exception to forbid execution, it would mean only CowEatGrass, and HorseEatGrass might exists as commands ? Thanks for your help, I am just beginning with these kinds of problem, and I would be glad to have some news from someone more experienced.

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  • Code contracts and inheritance

    - by DigiMortal
    In my last posting about code contracts I introduced you how to force code contracts to classes through interfaces. In this posting I will go step further and I will show you how code contracts work in the case of inherited classes. As a first thing let’s take a look at my interface and code contracts. [ContractClass(typeof(ProductContracts))] public interface IProduct {     int Id { get; set; }     string Name { get; set; }     decimal Weight { get; set; }     decimal Price { get; set; } }   [ContractClassFor(typeof(IProduct))] internal sealed class ProductContracts : IProduct {     private ProductContracts() { }       int IProduct.Id     {         get         {             return default(int);         }         set         {             Contract.Requires(value > 0);         }     }       string IProduct.Name     {         get         {             return default(string);         }         set         {             Contract.Requires(!string.IsNullOrWhiteSpace(value));             Contract.Requires(value.Length <= 25);         }     }       decimal IProduct.Weight     {         get         {             return default(decimal);         }         set         {             Contract.Requires(value > 3);             Contract.Requires(value < 100);         }     }       decimal IProduct.Price     {         get         {             return default(decimal);         }         set         {             Contract.Requires(value > 0);             Contract.Requires(value < 100);         }     } } And here is the product class that inherits IProduct interface. public class Product : IProduct {     public int Id { get; set; }     public string Name { get; set; }     public virtual decimal Weight { get; set; }     public decimal Price { get; set; } } if we run this code and violate the code contract set to Id we will get ContractException. public class Program {     static void Main(string[] args)     {         var product = new Product();         product.Id = -100;     } }   Now let’s make Product to be abstract class and let’s define new class called Food that adds one more contract to Weight property. public class Food : Product {     public override decimal Weight     {         get         {             return base.Weight;         }         set         {             Contract.Requires(value > 1);             Contract.Requires(value < 10);               base.Weight = value;         }     } } Now we should have the following rules at place for Food: weight must be greater than 1, weight must be greater than 3, weight must be less than 100, weight must be less than 10. Interesting part is what happens when we try to violate the lower and upper limits of Food weight. To see what happens let’s try to violate rules #2 and #4. Just comment one of the last lines out in the following method to test another assignment. public class Program {     static void Main(string[] args)     {         var food = new Food();         food.Weight = 12;         food.Weight = 2;     } } And here are the results as pictures to see where exceptions are thrown. Click on images to see them at original size. Violation of lower limit. Violation of upper limit. As you can see for both violations we get ContractException like expected. Code contracts inheritance is powerful and at same time dangerous feature. Although you can always narrow down the conditions that come from more general classes it is possible to define impossible or conflicting contracts at different points in inheritance hierarchy.

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  • Inheritance vs containment while extending a large legacy project

    - by Flot2011
    I have got a legacy Java project with a lot of code. The code uses MVC pattern and is well structured and well written. It also has a lot of unit tests and it is still actively maintained (bug fixing, minor features adding). Therefore I want to preserve the original structure and code style as much as possible. The new feature I am going to add is a conceptual one, so I have to make my changes all over the code. In order to minimize changes I decided not to extend existing classes but to use containment: class ExistingClass { // .... existing code // my code adding new functionality private ExistingClassExtension extension = new ExistingClassExtension(); public ExistingClassExtension getExtension() {return extension;} } ... // somewhere in code ExistingClass instance = new ExistingClass(); ... // when I need a new functionality instance.getExtension().newMethod1(); All functionality that I am adding is inside a new ExistingClassExtension class. Actually I am adding only these 2 lines to each class that needs to be extended. By doing so I also do not need to instantiate new, extended classes all over the code and I may use existing tests to make sure there is no regression. However my colleagues argue that in this situation doing so isn't a proper OOP approach, and I need to inherit from ExistingClass in order to add a new functionality. What do you think? I am aware of numerous inheritance/containment questions here, but I think my question is different.

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  • Modeling a cellphone bill: should I use single-table inheritance or polymorphic associations?

    - by Horace Loeb
    In my domain: Users have many Bills Bills have many BillItems (and therefore Users have many BillItems through Bills) Every BillItem is one of: Call SMS (text message) MMS (multimedia message) Data Here are the properties of each individual BillItem (some are common): My question is whether I should model this arrangement with single-table inheritance (i.e., one "bill_items" table with a "type" column) or polymorphism (separate tables for each BillItem type), and why.

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  • Who calls the Destructor of the class when operator delete is used in multiple inheritance.

    - by dicaprio-leonard
    This question may sound too silly, however , I don't find concrete answer any where else. With little knowledge on how late binding works and virtual keyword used in inheritance. As in the code sample, when in case of inheritance where a base class pointer pointing to a derived class object created on heap and delete operator is used to deallocate the memory , the destructor of the of the derived and base will be called in order only when the base destructor is declared virtual function. Now my question is : 1) When the destructor of base is not virtual, why the problem of not calling derived dtor occur only when in case of using "delete" operator , why not in the case given below: derived drvd; base *bPtr; bPtr = &drvd; //DTOR called in proper order when goes out of scope. 2) When "delete" operator is used, who is reponsible to call the destructor of the class? The operator delete will have an implementation to call the DTOR ? or complier writes some extra stuff ? If the operator has the implementation then how does it looks like , [I need sample code how this would have been implemented]. 3) If virtual keyword is used in this example, how does operator delete now know which DTOR to call? Fundamentaly i want to know who calls the dtor of the class when delete is used. Sample Code class base { public: base() { cout<<"Base CTOR called"<<endl; } virtual ~base() { cout<<"Base DTOR called"<<endl; } }; class derived:public base { public: derived() { cout<<"Derived CTOR called"<<endl; } ~derived() { cout<<"Derived DTOR called"<<endl; } }; I'm not sure if this is a duplicate, I couldn't find in search. int main() { base *bPtr = new derived(); delete bPtr;// only when you explicitly try to delete an object return 0; }

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  • JavaScript objects and Crockford's The Good Parts

    - by Jonathan
    I've been thinking quite a bit about how to do OOP in JS, especially when it comes to encapsulation and inheritance, recently. According to Crockford, classical is harmful because of new(), and both prototypal and classical are limited because their use of constructor.prototype means you can't use closures for encapsulation. Recently, I've considered the following couple of points about encapsulation: Encapsulation kills performance. It makes you add functions to EACH member object rather than to the prototype, because each object's methods have different closures (each object has different private members). Encapsulation forces the ugly "var that = this" workaround, to get private helper functions to have access to the instance they're attached to. Either that or make sure you call them with privateFunction.apply(this) everytime. Are there workarounds for either of two issues I mentioned? if not, do you still consider encapsulation to be worth it? Sidenote: The functional pattern Crockford describes doesn't even let you add public methods that only touch public members, since it completely forgoes the use of new() and constructor.prototype. Wouldn't a hybrid approach where you use classical inheritance and new(), but also call Super.apply(this, arguments) to initialize private members and privileged methods, be superior?

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  • Augmenting functionality of subclasses without code duplication in C++

    - by Rob W
    I have to add common functionality to some classes that share the same superclass, preferably without bloating the superclass. The simplified inheritance chain looks like this: Element -> HTMLElement -> HTMLAnchorElement Element -> SVGElement -> SVGAlement The default doSomething() method on Element is no-op by default, but there are some subclasses that need an actual implementation that requires some extra overridden methods and instance members. I cannot put a full implementation of doSomething() in Element because 1) it is only relevant for some of the subclasses, 2) its implementation has a performance impact and 3) it depends on a method that could be overridden by a class in the inheritance chain between the superclass and a subclass, e.g. SVGElement in my example. Especially because of the third point, I wanted to solve the problem using a template class, as follows (it is a kind of decorator for classes): struct Element { virtual void doSomething() {} }; // T should be an instance of Element template<class T> struct AugmentedElement : public T { // doSomething is expensive and uses T virtual void doSomething() override {} // Used by doSomething virtual bool shouldDoSomething() = 0; }; class SVGElement : public Element { /* ... */ }; class SVGAElement : public AugmentedElement<SVGElement> { // some non-trivial check bool shouldDoSomething() { /* ... */ return true; } }; // Similarly for HTMLAElement and others I looked around (in the existing (huge) codebase and on the internet), but didn't find any similar code snippets, let alone an evaluation of the effectiveness and pitfalls of this approach. Is my design the right way to go, or is there a better way to add common functionality to some subclasses of a given superclass?

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  • Is there a practical alternative to struct inheritance? (C#)

    - by Tim Coulter
    I am writing code that will populate the Margin, Padding and BorderThickness properties of classes in the System.Windows.Documents namespace. Each of these properties accepts a value in the form of a System.Windows.Thickness, which is a struct. However, I wish to associate some additional data with each of these property assignments, which may subsequently be retrieved by my code. If Thickness were a class, I would inherit from it and define properties in the subclass to store my additional data items. But since it is a struct, inheritance is not possible. Is there any practical way to achieve this, while maintaining type-compatibility with the properties I am populating? Thanks for your ideas, Tim

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  • for a single-table inheritance in rails, how do I know the 'type' when creating a record?

    - by Angela
    I have several models which are very similar: Contact_Emails, Contact_Letters, Contact_Calls -- and I think life could be easier making them into a Single Table Inheritance called Contact_Event. However, the way I have it set up now is when something is created for a Contact_Email, I have a dedicated controller that I call and know that I am passing the arguments that are approrpriate. For example, new_contact_email(contact, email). I then have: Emails.find(email.contact_id), etcera, all very specific to that Model. I'm not sure how I extract the class/models to use. For example, I currently have the following because I have separate controllers for each model: def do_event(contact, call_or_email_or_letter) model_name = call_or_email_or_letter.class.name.tableize.singularize link_to( "#{model_name.camelize}", send("new_contact_#{model_name}_path", :contact => contact, :status => 'done', :"#{model_name}" => call_or_email_or_letter ) ) end What I really want is to: link_to("#model_name.camelize}", send("new_contact_event_path(contact,call_or_email_or_letter)"

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  • How do I create the Controller for a Single Table Inheritance in Rails?

    - by Angela
    I am setting up the Single Table Inheritance, using ContactEvent as the Model that ContactEmail, ContactLetter, and ContactCall will all inherit. But I'm stumped on how to create the routing and the controller. For example, let's say I want to create a new ContactEvent with type Email. I would like a way to do the following: new_contact_event_path(contact, email) This would take the instance from Contact model and from Email model. Inside, I would imagine the contact_event_controller would need to know... @contact_event.type = (params[:email]) # get the type based on what was passed in? @contact_event.event_id = (params[:email]) #get the id for the correct class, in this case Email.id Just not sure how this works....

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  • Reload Grid not working for mutiple jqgrid

    - by arun chaudhary
    I am using jqgrid.My page has three tabs and each tab contains a different grid.All grids have different ids.The content of tabs is fetched via AJAX request lazily.Now after all three grids are rendered and i try to reload grid via function jQuery("#myOffersTable").trigger('reloadGrid'); Only the grid which loaded last reloads and it doesn't work for other grids. eg if grids load seq is : 1-2-3 then this code will only work for grid 3 but if seq is 3-2-1 then it will work only for 1. But if i try reloading grids using reload button on navigator bar it works fine. Any help would be appreciated. Thanks Arun

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  • ASP.NET MVC Pass mutiple params from getJson to controller

    - by andyJ
    Hi, I am making a call to a controller action in javascript using the getJson method. I need to pass two parameters to my action method on the controller, but I am struggling to do so. I do not fully understand the routing tables and not sure if this is what I need to use to get this working. Please see example below of what I am trying to do. var action = "<%=Url.Content('~/Postcode/GetAddressResults/')%>" + $get("Premise").value + "/" + $get("SearchPostcode").value $.getJSON(action, null, function(data) { $("#AddressDropDown").fillSelect(data); }); This is my route which I don't understand how to make use of... routes.MapRoute( "postcode", "Postcode/GetAddressResults/{premise}/{postcode}", new { controller = "Motor", action = "GetAddressResults", premise = "", postcode = "" });

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  • C# Event handling In mutiple level /classes

    - by Amitd
    Hi, I have 3 classes A,B,C . Class A creates B .. class B creates class C. Class C raises events after some action/operation with some data, which is handled by event handler in Class B. Now I want to be handle or pass the same raised event data to Class A. I know i can raise another event from class B and handle it in A but is there a better way of handling such events?? Thx

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  • WCF Blocking problem with mutiple clients!!

    - by Marcel
    Hi I seem to have a blocking issue with WCF. Say I have two users and each have created their own instance of a class exposed on a WCF host using net.tcp with endpoint something like this "net.tcp://localhost:32000/SymHost/". The class is PerSession context and concurrency is reentrant. The class exposes two methods Alive() which return a bool of true straight away and an AliveWait which I inserted which does a Thread.Sleep for 4 seconds before returning true (testing purposes). Now client 1 calls AliveWait() during which time he is blocked which is fair enough but then if client 2 makes a call to Alive() on its own instance he has to wait until client 1's call is returned - this behaviour is not what I would have expected? I would have expected client 2 to carry on as if nothing has happened or is this to do with the fact that they both share the same endpoint? Can anyone explain what is going on and how I can make sure that client 2 can call its own instance uninterrupted? Any help much appreciated!

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  • Parsing mutiple xml files in android

    - by cppdev
    Hi, I ma writing an application where I have to parse multiple xml files as a response from a server. Till now, I have written different xml parser classes for each xml depepending on the tags present in different xmls ? Can I combine all xml parser classes and write a single xml parser that handles all different tags in different xmls ? Will it work ? Will combining xml parser classes add an overhead because xml parser will check for every tag irrespective of whether that is part of file or not ? Please help.

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  • Cheap ASP.NET Hosting - Mutiple Domains

    - by tyndall
    Can anybody recommend some quality ASP.NET hosting providers that allow you to multiple domains without making you use a "reseller" account or purchase multiple accounts. I really only need email accounts for one of the domains. I'm looking for something about $20 to $45 USD.

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  • Problem in mutiple :dependent=> :destroy when multiple polymorphic is true

    - by piemesons
    I have four models question, answer, comment and vote.Consider it same as stackoverflow. Question has_many comments Answers has_many comments Questions has_many votes answers has_many votes comments has_many votes Here are the models (only relevant things) class Comment < ActiveRecord::Base belongs_to :commentable, :polymorphic => true has_many :votes, :as => :votable, :dependent => :destroy end class Question < ActiveRecord::Base has_many :comments, :as => :commentable, :dependent => :destroy has_many :answers, :dependent => :destroy has_many :votes, :as => :votable, :dependent => :destroy end class Vote < ActiveRecord::Base belongs_to :votable, :polymorphic => true end class Answer < ActiveRecord::Base belongs_to :question, :counter_cache => true has_many :comments, :as => :commentable , :dependent => :destroy end Now the problem is whenever i am trying to delete any question/answer/comment its giving me an error NoMethodError in QuestionsController#destroy undefined method `each' for 0:Fixnum if i remove this line from any of the model (question/answer/comment) has_many :votes, :as => :votable, :dependent => :destroy then it works perfectly. It seems there is a problem while deleting the records active record is not able to find out the proper path because of multiple joins within the tables.

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  • How to draw mutiple rectangles using c#

    - by Nivas
    I have drawn and saved the Rectangle on the image i loaded in the picture box. How i like to draw multiple rectangles for that i tried array in the rectangle but it gives error ("Object reference not set to an instance of an object." (Null reference Exception was unhandled). enter code here private void pictureBox1_MouseDown(object sender, MouseEventArgs e) { if (mybitmap == null) { mybitmap = new Bitmap(sz.Width, sz.Height); } rect = new Rectangle(e.X, e.Y, 0, 0); this.Invalidate(); } private void pictureBox1_MouseMove(object sender, MouseEventArgs e) { if (stayToolStripMenuItem.Checked == true) { switch (e.Button) { case MouseButtons.Left: { rect = new Rectangle(rect.Left, rect.Top, e.X - rect.Left, e.Y - rect.Top); pictureBox1.Invalidate(); break; } } } } private void pictureBox1_Paint(object sender, PaintEventArgs e) { if (stayToolStripMenuItem.Checked == true) { button1.Visible = true; button2.Visible = true; if (mybitmap == null) { return; } using (g = Graphics.FromImage(mybitmap)) { using (Pen pen = new Pen(Color.Red, 2)) { //g.Clear(Color.Transparent); e.Graphics.DrawRectangle(pen, rect); label1.Top = rect.Top; label1.Left = rect.Left; label1.Width = rect.Width; label1.Height = rect.Height; if (label1.TextAlign == ContentAlignment.TopLeft) { e.Graphics.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawRectangle(pen, rect); } } } } } How can i do this.....

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  • C# Lack of Static Inheritance - What Should I Do?

    - by yellowblood
    Alright, so as you probably know, static inheritance is impossible in C#. I understand that, however I'm stuck with the development of my program. I will try to make it as simple as possible. Lets say our code needs to manage objects that are presenting aircrafts in some airport. The requirements are as follows: There are members and methods that are shared for all aircrafts There are many types of aircrafts, each type may have its own extra methods and members. There can be many instances for each aircraft type. Every aircraft type must have a friendly name for this type, and more details about this type. For example a class named F16 will have a static member FriendlyName with the value of "Lockheed Martin F-16 Fighting Falcon". Other programmers should be able to add more aircrafts, although they must be enforced to create the same static details about the types of the aircrafts. In some GUI, there should be a way to let the user see the list of available types (with the details such as FriendlyName) and add or remove instances of the aircrafts, saved, lets say, to some XML file. So, basically, if I could enforce inherited classes to implement static members and methods, I would enforce the aircraft types to have static members such as FriendlyName. Sadly I cannot do that. So, what would be the best design for this scenario?

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