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  • Third-Grade Math Class

    - by andyleonard
    An Odd Thing Happened... ... when I was in third grade math class: I was handed a sheet of arithmetic problems to solve. There were maybe 20 problems on the page and we were given the remainder of the class to complete them. I don't remember how much time remained in the class, I remember I finished working on the problems before my classmates. That wasn't the odd part. The odd part was that I started working on the first problem, concentrating pretty hard. I worked the sum and moved to the next...(read more)

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  • Ways to ensure unique instances of a class?

    - by Peanut
    I'm looking for different ways to ensure that each instance of a given class is a uniquely identifiable instance. For example, I have a Name class with the field name. Once I have a Name object with name initialised to John Smith I don't want to be able to instantiate a different Name object also with the name as John Smith, or if instantiation does take place I want a reference to the orginal object to be passed back rather than a new object. I'm aware that one way of doing this is to have a static factory that holds a Map of all the current Name objects and the factory checks that an object with John Smith as the name doesn't already exist before passing back a reference to a Name object. Another way I could think of off the top of my head is having a static Map in the Name class and when the constructor is called throwing an exception if the value passed in for name is already in use in another object, however I'm aware throwing exceptions in a constructor is generally a bad idea. Are there other ways of achieving this?

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  • How to name an subclass that add a minor, detailed thing?

    - by Louis Rhys
    What is the most concise (yet descriptive) way of naming a subclass that only add a specific minor thing to the parent? I encountered this case a lot in WPF, where sometime I have to add a small functionality to an out-of-the-box control for specific cases. Example: TreeView doesn't change the SelectedItem on right-click, but I have to make one that does in my application. Some possible names are TreeViewThatChangesSelectedItemOnRightClick (way too wordy and maybe difficult to read because there is so many words concantenated together) TreeView_SelectedItemChangesOnRightClick (slightly more readable, but still too wordy and the underscore also breaks the normal convention for class names) TreeViewThatChangesSIOnRC (non-obvious acronym), ExtendedTreeView (more concise, but doesn't describe what it is doing. Besides, I already found a class called this in the library, that I don't want to use/modify in my application). LouisTreeView, MyTreeView, etc. (doesn't describe what it is doing). It seems that I can't find a name which sounds right. What do you do in situation like this?

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  • Best practice to propagate preferences of application

    - by Shebuka
    What is your approach with propagation to all classes/windows of preferences/settings of your application? Do you share the preference_manager class to all classes/windows who need it or you make variables in each classes/windows and update them manually each time setting are changed? Currently I have a PreferencesInterface class that hold all preferences and is responsible to default all values with a dedicated method called on create and when needed, all values are public, so non getters/setters, also it have virtual SavePreferences/LoadPreferences methods. Then I have PreferencesManager that extends from PreferencesInterface and is responsible for actually implementation of SavePreferences/LoadPreferences. I've made this basically for cross-platform so that every platform can have a different implementation of actual storage (registry, ini, plist, xml, whatever).

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  • Should a domain expert make class diagrams?

    - by Matthieu
    The domain expert in our team uses UML class diagrams to model the domain model. As a result, the class diagrams are more of technical models rather than domain models (it serves of some sort of technical specifications for developpers because they don't have to do any conception, they just have to implement the model). In the end, the domain expert ends up doing the job of the architect/technical expert right? Is it normal for a domain expert (not a developer or technical profile) to do class diagrams? If not, what kind of modeling should he be using?

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  • Why use link classes in oql instead of classes that contain links

    - by Isaac
    itop abstracts its very complex database design with an object query language (oql). For this there are classes definded, like 'Ticket' and 'Server'. Now a Ticket usually is linked to a Server. In my naive way I would give the Ticket class an attribute 'affected_server_list', where I could reference the affected servers. itop does it different: neither Servers nor Tickets know of each other. Instead there is a class 'linkTicketToServer', which provides the link between the two. The first thing I noticed is that it makes oql queries more complex. So I wondered why they designed it this way. One thing that occured to me is that it allows for more flexiblity, in that I can add links without modifying the original classes. Is this allready why one would implement it this way, or are there other reasons for this kind of design?

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  • Exporting XNA class library as a DLL file

    - by Will Bagley
    I have downloaded an open source project that I intend to use with my current game. The download came with all the class files from the original project as well as a pre-compiled DLL file representing the project. I was able to easily link this DLL with my current project and get it working just fine, no problems there. The problem I now have is that I want to make a couple of changes to the original libraries (extend its functionality a bit to better suit my needs) and re-export the class library as a DLL again, but I have no clue how to do this. Is there some simple way in VS where I can just take the class library and export/compile it as a DLL file again or is there more to it than that? This seems like something that should be pretty simple but my efforts to find an answer have so far come up with nothing. Thanks in advance.

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  • Torque2D, Class vs Datablock

    - by Max Kielland
    I'm scripting my first game with Torque2D and have not fully understood the difference between "Class" and Datablock. To me it seems like Datablock is similar to a struct in C/C++ or a Record in Pascal. If I create Datablocks with new, are they instantiated in the same way as a "Class"? I have a large TileMap and need to attach some information to each Tile. I was thinking to use a Datablock, as a struct, to attach this information to the tile's CustomData property. The two questions are: What is a Datablock and should I use a Datablock or a "Class" for this tile information?

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  • UML Class diagrams with Java packages?

    - by loosebruce
    I am trying to model in UML 2.0 a Java servlet application that has three classes Servlet class; essentially a main class that acts as the controller DatabaseLogic; contains methods for database operations XMLBuilder; builds an XML from a query result string The classes use a variety of packages from the Java library. I am unsure how to model this in UML Do I have to create a package and show which libraries are used for each individual class or can I just have one large package in the diagram with all the libraries showing which classes have dependencies on which. As per this diagram This is my first time working with java properly (im a C++ guy) Apart from being a bit messy , is this a correct UML representation of the system I described? Does a Package in UML mean the same as a Package in Java?

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  • Is it evil to model JSON responses to classes when they are mostly smilar?

    - by Aybe
    Here's the problem : While implementing a C# wrapper for an online API (Discogs) I've been faced to a dilemma : quite often the responses returned have mostly similar members and while modeling these responses to classes, some questions surfaces on which way to go would be the best. Example : Querying for a 'release' or a 'master' will return an object that contains an array of 'artist', however these 'artists' do not exactly have the same members. Currently I decided to represent these 'artists' as a single 'Artist' class, against having respective 'ReleaseArtist' and 'MasterArtist' classes which soon becomes very confusing even though another problem arises : when a category (master or release) does not return these members, they will be null. Though it might sound confusing as well I find it less confusing than the former situation as I've tackled the problem by simply not showing null members when visualizing these objects. Is this the right approach to follow ? An example of these differences : public class Artist { public List<Alias> Aliases { get; set; } public string DataQuality { get; set; } public List<Image> Images { get; set; } public string Name { get; set; } public List<string> NameVariations { get; set; } public string Profile { get; set; } public string Realname { get; set; } public string ReleasesUrl { get; set; } public string ResourceUrl { get; set; } public string Uri { get; set; } public List<string> Urls { get; set; } } public class ReleaseArtist { public string Join { get; set; } public string Name { get; set; } public string Anv { get; set; } public string Tracks { get; set; } public string Role { get; set; } public string ResourceUrl { get; set; } public int Id { get; set; } }

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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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  • Functions returning pointers

    - by fg nu
    C++ noob here. I have a very basic question about a construct I found in the C++ book I am reading. // class declaration class CStr { char sData[256]; public: char* get(void); }; // implementation of the function char* CStr::get(void) { return sData; } So the Cstr::get function is obviously meant to return a character pointer, but the function is passing what looks like the value (return sData). Does C++ know to return the address of the returned object? My guess would have been that the function definition would be return &sData.

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  • overriding implemented base class methods

    - by user793468
    I read somewhere that the chain of inheritance breaks when you alter a behavior from derived class. What does "altering a behavior" mean here? Is overriding an already implemented method in base class considered as "altering behavior"? Or, does the author mean altering method signatures and the output? Also, I ready Duplicating code is not a good practice, and its a maintenance nightmare. Again, does overriding an already implemented method in base class considered "Duplicating code"? If not, what would be considered as "Duplicating code"? I

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  • How to ensure that a member variable is initialized before calling a class method

    - by Omkar Ekbote
    There's a class with a parametrized constructor that initializes a member variable. All public methods of the class then use this member variable to do something. I want to ensure that the caller always creates an object using the parametrized constructor (there is also a setter for this member variable) and then call that object's methods. In essence, it should be impossible for the caller to call any method without setting a value to the member variable (either by using the parametrized constructor or the setter). Currently, a caller can simply make an object using the default constructor and then call that object's method - I want to avoid checking whether or not the member variable is set in each and every one of the 20-odd methods of the class (and throw an exception if it is not). Though a runtime solution is acceptable (better than the one I mentioned above); a compile-time solution is preferable so that any developer will not be allowed to make that mistake and then waste hours debuggging it!

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  • Why is it good to split a program into multiple classes?

    - by user1276078
    I'm still a student in high school (entering 10th grade), and I have yet to take an actual computer course in school. Everything I've done so far is through books. Those books have taught me concepts such as inheritance, but how does splitting a program into multiple classes help? The books never told me. I'm asking this mainly because of a recent project. It's an arcade video game, sort of like a flash game as some people have said (although I have no idea what a flash game is). The thing is, it's only one class. It works perfectly fine (a little occasional lag however) with just one class. So, I'm just asking how splitting it into multiple classes would help it. This project was in JAVA and I am the only person working on it, for the record.

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  • Should single purpose utility app use a class

    - by jmoreno
    When writing a small utility app, that does just one thing, should that one thing be encapsulated in a seperate class, or just let it be part of whatever class/module is used to start the application? I.e. Main would consist of 2 or three lines calling the constructor and then the DoIt methods, nothing else. Or should Main be the DoIt method, with whatever functions it needs added to the main class? Asking because I want to get some alternative perspective, but couldn't find a similar question. If my google-fu is bad and there's a dup, please close.

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  • Should Equality be commutative within a Class Hierachy?

    - by vossad01
    It is easy to define the Equals operation in ways that are not commutative. When providing equality against other types, there are obviously situations (in most languages) were equality not being commutative is unavoidable. However, within one's own inheritance hierarchy where the root base class defines an equality member, a programmer has more control. Thus you can create situations where (A = B) ? (B = A), where A and B both derive from base class T Substituting the = with the appropriate variation for a given language. (.Equals(_), ==, etc.) That seems wrong to me, however, I recognize I may be biased by background in Mathematics. I have not been in programming long enough to know what is standard/accepted/preferred practice when programming. Do most programmers just accept .Equals(_)may not be commutative and code defensibly. Do they expect commutativity and get annoyed if it is not. In short, when working in a class hierarchy, should effort me made to ensure Equality is commutative?

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  • Rendering a derived partial view with Html.RenderPartial

    - by FreshCode
    Calling Html.RenderPartial("~/Views/Payments/MyControl.ascx"); from a view works if Method.ascx is a control that directly inherits System.Web.Mvc.ViewUserControl. However, if the control inherits a new class that derives from System.Web.Mvc.ViewUserControl, the call to Html.RenderPartial("~/Views/Payments/MyDerivedControl.ascx"); fails, reporting that no such view exists. Example derived ViewUserControl: class MyDerivedControl : System.Web.Mvc.ViewUserControl { public Method() { ViewData["SomeData"] = "test"; } } Is there a workaround, or is there another way I should be doing this? Perhaps an HTML helper?

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  • How to change default image of derived ToolStripButton?

    - by Special Touch
    It seems like a simple task. Create a C# class that derives from ToolStripButton. The derived ToolStripButton should behave exactly the same as the parent class in the designer and the application, except that the default image should be different. Surprisingly just changing the constructor is not sufficient: public CustomToolStripButton() { base.Image = (Image) new Bitmap(typeof(CustomToolStripButton), "CustomImage.bmp"); } When the ToolStripButton is displayed in the designer, the original default image is shown. There must be a simple solution. What could it be?

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  • Pointers to Derived Class Objects Losing vfptr

    - by duckworthd
    To begin, I am trying to write a run-of-the-mill, simple Ray Tracer. In my Ray Tracer, I have multiple types of geometries in the world, all derived from a base class called "SceneObject". I've included the header for it here. /** Interface for all objects that will appear in a scene */ class SceneObject { public: mat4 M, M_inv; Color c; SceneObject(); ~SceneObject(); /** The transformation matrix to be applied to all points of this object. Identity leaves the object in world frame. */ void setMatrix(mat4 M); void setMatrix(MatrixStack mStack); void getMatrix(mat4& M); /** The color of the object */ void setColor(Color c); void getColor(Color& c); /** Alter one portion of the color, leaving the rest as they were. */ void setDiffuse(vec3 rgb); void setSpecular(vec3 rgb); void setEmission(vec3 rgb); void setAmbient(vec3 rgb); void setShininess(double s); /** Fills 'inter' with information regarding an intersection between this object and 'ray'. Ray should be in world frame. */ virtual void intersect(Intersection& inter, Ray ray) = 0; /** Returns a copy of this SceneObject */ virtual SceneObject* clone() = 0; /** Print information regarding this SceneObject for debugging */ virtual void print() = 0; }; As you can see, I've included a couple virtual functions to be implemented elsewhere. In this case, I have only two derived class -- Sphere and Triangle, both of which implement the missing member functions. Finally, I have a Parser class, which is full of static methods that do the actual "Ray Tracing" part. Here's a couple snippets for relevant portions void Parser::trace(Camera cam, Scene scene, string outputFile, int maxDepth) { int width = cam.getNumXPixels(); int height = cam.getNumYPixels(); vector<vector<vec3>> colors; colors.clear(); for (int i = 0; i< width; i++) { vector<vec3> ys; for (int j = 0; j<height; j++) { Intersection intrsct; Ray ray; cam.getRay(ray, i, j); vec3 color; printf("Obtaining color for Ray[%d,%d]\n", i,j); getColor(color, scene, ray, maxDepth); ys.push_back(color); } colors.push_back(ys); } printImage(colors, width, height, outputFile); } void Parser::getColor(vec3& color, Scene scene, Ray ray, int numBounces) { Intersection inter; scene.intersect(inter,ray); if(inter.isIntersecting()){ Color c; inter.getColor(c); c.getAmbient(color); } else { color = vec3(0,0,0); } } Right now, I've forgone the true Ray Tracing part and instead simply return the color of the first object hit, if any. As you have no doubt noticed, the only way the computer knows that a ray has intersected an object is through Scene.intersect(), which I also include. void Scene::intersect(Intersection& i, Ray r) { Intersection result; result.setDistance(numeric_limits<double>::infinity()); result.setIsIntersecting(false); double oldDist; result.getDistance(oldDist); /* Cycle through all objects, making result the closest one */ for(int ind=0; ind<objects.size(); ind++){ SceneObject* thisObj = objects[ind]; Intersection betterIntersect; thisObj->intersect(betterIntersect, r); double newDist; betterIntersect.getDistance(newDist); if (newDist < oldDist){ result = betterIntersect; oldDist = newDist; } } i = result; } Alright, now for the problem. I begin by creating a scene and filling it with objects outside of the Parser::trace() method. Now for some odd reason, I cast Ray for i=j=0 and everything works wonderfully. However, by the time the second ray is cast all of the objects stored in my Scene no longer recognize their vfptr's! I stepped through the code with a debugger and found that the information to all the vfptr's are lost somewhere between the end of getColor() and the continuation of the loop. However, if I change the arguments of getColor() to use a Scene& instead of a Scene, then no loss occurs. What crazy voodoo is this?

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  • Add custom Model Binders for derived objects and their base

    - by mare
    My class diagram: BaseContentClass Page inherits BaseContentClass Tab inherits BaseContentClass ... If I do this ModelBinders.Binders.Add(typeof(BaseContentObject), new BaseContentObjectCommonPropertiesBinder()); then when in controller action parameter of type Tab appears, custom model binder is not fired. It gets fired if I do this: ModelBinders.Binders.Add(typeof(Tab), new BaseContentObjectCommonPropertiesBinder()); But I don't want to go writing "n" number of Add statements in my global.asax.cs to associate all the derived classes with my custom model binder, do I? I don't know if I have any other option.

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  • navigation framework in silverlight 3 skipping constructor when usercontrol is of a derived type

    - by tarren
    Hi: I am using the NavigationFramework in Silverlight 3, and am running into issues where the constructor of the UserControl in the xaml I am loading is not being called, and I believe this is because the UserControl in the xaml I am calling is actually derived from another user control. I have stepped through the debugger with specific break points and the constructor is being ignored completey. I have MyWindowBlue which is of type uctrlBaseMyWindow. The constructor for uctrlBaseMyWindow is being called when the xaml is 'navigated to' but the constructor for MyWindowBlue is being ignored. This is not the case if I add the user control via markup directly. Anyone else have this issue? The code I am using to navigate to the MyWindowBlue is this.MyContentFrame.Navigate(new Uri("/Controls/uctrlMyWindowBlue.xaml", UriKind.Relative)); Has anyone run into this or could offer any help? Thanks

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  • Getting all types from an assembly derived from a base class

    - by CaptnCraig
    I am trying to examine the contents of an assembly and find all classes in it that are directly or indirectly derived from Windows.Forms.UserControl. I am doing this: Assembly dll = Assembly.LoadFrom(filename); var types = dll.GetTypes().Where(x => x.BaseType == typeof(UserControl)); But it is giving an empty list because none of the classes directly extend UserControl. I don't know enough about reflection to do it quickly, and I'd rather not write a recursive function if I don't have to.

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  • c++ template: 'is not derived from type'

    - by Allan
    I do not understand why this code is not valid: #include <vector> template <typename T> class A{ public: A() { v.clear(); } std::vector<A<T> *>::const_iterator begin(){ return v.begin(); } private: std::vector<A<T> *> v; }; When compiling it with gcc, it get the following error: test.cpp:8: error: type 'std::vector<A<T>*, std::allocator<A<T>*> >' is not derived from type 'A<T>' test.cpp:8: error: expected ';' before 'begin' test.cpp:12: error: expected `;' before 'private' What is wrong, and how to fix it??

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  • Calculation of derived field in sql

    - by Matt
    Taking Sql this quarter and not having any luck with the following question: The height of players in feet (inches/12). Include their name. Hint: Calculation or derived field. Be sure to give the calculated field a column header. We're learning the basic Select statment and didn't find any reference on how to make custom data at w3schools. I'm using Microsoft SQL server Management Express Here's my statment so far: select nameLast, nameFirst, height from Master where height (I assume its something like 'Player_Height' = height/12) order by nameLast, nameFirst, height Thanks for the help

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