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  • Help to understand the abstract factory pattern

    - by Chobeat
    I'm learning the 23 design patterns of the GoF. I think I've found a way to understand and simplify how the Abstract Factory works but I would like to know if this is a correct assumption or if I am wrong. What I want to know is if we can see the result of the Abstract Factory method as a matrix of possible products where there's a Product for every "Concrete Factory" x "AbstractProduct" where the Concrete Factory is a single implementation among the implementations of an AbstractFactory and an AbstractProduct is an interface among the interfaces to create Products. Is this correct or am I missing something?

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  • The Singleton Pattern

    - by Darren Young
    Hi, I am a new programmer (4 months into my first job) and have recently taken an interest in design patterns. One that I have used recently is the Singleton. However, looking at some comments on this thread Overused or abused programming techniques .......it has some bad feedback. Come somebody explain why? I have found it useful in some places, however I could probably have achieved the same without it using a static class. Thanks.

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  • How to fix the copy/paste-pattern?

    - by Lenny222
    Where i work, people (consultants) feel pressed to release features as fast as possible. So instead of spending too much time on thinking about how to do things the right way or because they don't want to break anything, code gets copied from different modules and modified. It's not easy to prevent this, since the code base is open to the whole company. Lots of people work on this. Now that the mess is there already, what is the best way to remove those redundancies without breaking too much?

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  • wbadmin incremental system state backup

    - by user74513
    I am doing system state backups on a Windows Server 2008 R2 Enterprise (Service Pack 1) machine and expected the backups after the first one to be incremental. However with each backup a new directory with vhd files are created and the vhd files are almost the same size as the with the first backup. So the backups does not seem to be incremental. I used the following command to do the backup: wbadmin start systemstatebackup -backupTarget:f: I played around with the settings under "Configure Performance Settings" in the Windows Server Backup plugin in Server Manager but according to the description at the top of the dialog these settings are not applied to system state backups. Are there any settings available for wbadmin system state backup to make the backups incremental?

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  • Role of an entity state in a component based system?

    - by Paul
    Component-based entity systems are all the rage these days; everyone seems to agree they are the way to go, but no one really has a definitive implementation of such a system. I was wondering, what role do entity states (walking-left, standing, jumping, etc) have in a CBS? Do they act like controllers (i.e. they handle events and change the entity's attributes based on those events)? What about cases where a state would, for example, require that the entity enters no-clip mode? Should, that state, when it enters, maybe set the CollisionComponent of the entity to a null pointer or something? (Then, on exit, the state should restore the entity's CollisionComponent to its previous state.) Also, I guess it's the current state's job to change the entity's state to something else, right?

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  • RESTFul: state changing actions

    - by Miro Svrtan
    I'am planning to build RESTfull API but there are some architectural questions that are creating some problems in my head. Adding backend bussiness logic to clients is option that I would like to avoid since updating multiple client platforms is hard to maintain in real time when bussiness logic can rapidly change. Lets say we have article as a resource ( api/article ), how should we implement actions like publish, unpublish,activate or deactivate and so on but to try to keep it as simple as possible? 1) Should we use api/article/{id}/{action} since a lot of backend logic can happen there like pushing to remote locations or change of multiple properties. Probably the hardest thing here is that we need to send all article data back to API for updating and multiuser work could not be implemented. For instance editor could send 5 seconds older data and overwrite fix that some other journalist just did 2 seconds ago and there is no way that I could explain to clients this since those publishing an article is really not in any way connected to updating the content. 2) Creating new resource can also be an option, api/article-{action}/id , but then returned resource would not be article-{action} but article which I'am not sure if this is proper. Also in server side code article class is handling actuall work on both resource and I'm not sure if this goes against RESTfull thinking Any suggestions are welcomed..

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  • Masking OpenGL texture by a pattern

    - by user1304844
    Tiled terrain. User wants to build a structure. He presses build and for each tile there is an "allow" or "disallow" tile sprite added to the scene. FPS drops right away, since there are 600+ tiles added to the screen. Since map equals screen, there is no scrolling. I came to an idea to make an allow grid covering the whole map and mask the disallow fields. Approach 1: Create allow and disallow grid textures. Draw a polygon on screen. Pass both textures to the fragment shader. Determine the position inside the polygon and use color from allowTexture if the fragment belongs to the allow field, disallow otherwise Problem: How do I know if I'm on the field that isn't allowed if I cannot pass the matrix representing the map (enum FieldStatus[][] (Allow / Disallow)) to the shader? Therefore, inside the shader I don't know which fragments should be masked. Approach 2: Create allow texture. Create an empty texture buffer same size as the allow texture Memset the pixels of the empty texture to desired color for each pixel that doesn't allow building. Draw a polygon on screen. Pass both textures to the fragment shader. Use texture2 color if alpha 0, texture1 color otherwise. Problem: I'm not sure what is the right way to manipulate pixels on a texture. Do I just make a buffer with width*height*4 size and memcpy the color[] to desired coordinates or is there anything else to it? Would I have to call glTexImage2D after every change to the texture? Another problem with this approach is that it takes a lot more work to get a prettier effect since I'm manipulating the color pixels instead of just masking two textures. varying vec2 TexCoordOut; uniform sampler2D Texture1; uniform sampler2D Texture2; void main(void){ vec4 allowColor = texture2D(Texture1, TexCoordOut); vec4 disallowColor = texture2D(Texture2, TexCoordOut); if(disallowColor.a > 0){ gl_FragColor= disallowColor; }else{ gl_FragColor= allowColor; }} I'm working with OpenGL on Windows. Any other suggestion is welcome.

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  • Game state management (Game, Menu, Titlescreen, etc)

    - by munchor
    Basically, in every single game I've made so far, I always have a variable like "current_state", which can be "game", "titlescreen", "gameoverscreen", etc. And then on my Update function I have a huge: if current_state == "game" game stuf ... else if current_state == "titlescreen" ... However, I don't feel like this is a professional/clean way of handling states. Any ideas on how to do this in a better way? Or is this the standard way?

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  • Current state of the art for holographic displays?

    - by kamziro
    In another thread I was asking about independent arcade system development, and partly it was because I'm interested in using available 3D holographic technology for the displays. I saw one which involved a rotating mirror at very high speeds, so that's probably not going to be too feasible (I'd hate to think of what happens when something goes wrong). However, I looked around for videos from trade shows, and I found this: http://www.youtube.com/watch?v=Vl0EIngM-RA But information is scarce, and I'm led to believe it's just using mirrors and reflections, and does not convey true 3D depth like the one using rotating mirrors at high speed: http://www.youtube.com/watch?v=YKCUGQ-uo8c So yeah, does anyone know if there's something better available today?

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  • Authorization design-pattern / practice?

    - by Lawtonfogle
    On one end, you have users. On the other end, you have activities. I was wondering if there is a best practice to relate the two. The simplest way I can think of is to have every activity have a role, and assign every user every role they need. The problem is that this gets really messy in practice as soon as you go beyond a trivial system. A way I recently designed was to have users who have roles, and roles have privileges, and activities require some combinations of privileges. For the trivial case, this is more complex, but I think it will scale better. But after I implemented it, I felt like it was overkill for the system I had. Another option would be to have users, who have roles, and activities require you to have a certain role to perform with many activities sharing roles. A more complex variant of this would given activities many possible roles, which you only needed one of. And an even more complex variant would be to allow logical statements of role ownership to use an activity (i.e. Must have A and (B exclusive or C) and must not have D). I could continue to list more, but I think this already gives a picture. And many of these have trade offs. But in software design, there are oftentimes solutions, while perhaps not perfect in every possible case, are clearly top of the pack to an extent it isn't even considered opinion based (i.e. how to store passwords, plain text is worse, hashing better, hashing and salt even better, despite the increased complexity of each level) (i.e. 2, Smart UI designs for applications are bad, even if it is subjective as to what the best design is). So, is there a best practice for authorization design that is not purely opinion based/subjective?

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  • C# Cursor stuck on busy state

    - by Ben
    So I implemented a fixed time step loop for my C# game. All it does at the moment is make a square bounce around the screen. The problem I'm having is that when I execute the program, the window doesn't allow me to close the program and the cursor is stuck on the busy icon. I have to go into visual studio and stop the program manually. Here's the loop at the moment public void run() { int updates = 0; int frames = 0; double msPerTick = 1000.0 / 60.0; double threshhold = 0; long lastTime = getCurrentTime(); long lastTimer = getCurrentTime(); while (true) { long currTime = getCurrentTime(); threshhold += (currTime - lastTime) / msPerTick; lastTime = currTime; while (threshhold >= 1) { update(); updates++; threshhold -= 1; } this.Refresh(); frames++; if ((getCurrentTime() - lastTimer) >= 1000) { this.Text = updates + " updates and " + frames + " frames per second"; updates = 0; frames = 0; lastTimer += 1000; } } }

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  • Algorithmic Forecasting and Pattern Recognition

    - by Ryan King
    Say a user could enter project data into my software. Each project has 2 variables "size" and "work" and they're related but the relationship is not known. Is there a way to programmatically determine the relationship between the variables based on previous data and forecast the amount of work provided if only given the size of the project in the future? For Example, say the user had manually entered the following projects. Project 1 - Size:1, Work: 4 Project 2 - Size:2, Work: 7 Project 3 - Size:3, Work: 10 Project 4 - Size:4, Work: x What should I look into to be able to programmatically determine, that Work = Size*3+1 and therefor be able to say that x=13?

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  • Which pattern is best for large project

    - by shamim
    I have several years of software development experience, but I am not a keen and adroit programmer, to perform better I need helping hands. Recently I engaged in an ERP project. For this project want a very effective structure, which will be easily maintainable and have no compromise about performance issue. Below structures are now present in my old projects. Entity Layer BusinessLogic Layer. DataLogic Layer UI Layer. Bellow picture describe how they are internally connected. For my new project want to change my project structure, I want to follow below steps: Core Layer(common) BLL DAL Model UI Bellow picture describe how they are internally connected. Though goggling some initial type question’s are obscure to me, they are : For new project want to use Entity framework, is it a good idea? Will it increase my project performance? Will it more maintainable than previous structure? Entity Framework core disadvantages/benefits are? For my project need help to select best structure. Will my new structure be better than the old one?

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  • Which parallel pattern to use?

    - by Wim Van Houts
    I need to write a server application that fetches mails from different mail servers/mailboxes and then needs to process/analyze these mails. Traditionally, I would do this multi-threaded, launching a thread for fetching mails (or maybe one per mailbox) and then process the mails. We are moving more and more to servers where we have 8+ cores, so I would like to make use of these cores as much as possible (and not use 1 at 100% and leave the seven others untouched). So conceptually, as an example, it would be nice that I could write the application in such a way that two cores are "continuously" fetching emails and four cores are "continuously" processing/analyzing the emails (since processing and analyzing mails is more CPU intensive than fetching mails). This seems like a good concept, but after studying some parallel patterns, I'm not really sure how this is best implemented. None of the patterns really fit. I'm working in VS2012, native C++, but I guess from a design point of view this does not really matter and just some pointers on how to organize this would be great!

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  • Design Pattern for Skipping Steps in a Wizard

    - by Eric J.
    I'm designing a flexible Wizard system that presents a number of screens to complete a task. Some screens may need to be skipped based on answers to prompts on one or more previous screens. The conditions to skip a given screen need to be editable by a non-technical user via a UI. Multiple conditions need only be combined with and. I have an initial design in mind, but it feels inelegant. I wonder if there's a better way to approach this class of problem. Initial Design UI where The first column allows the user to select a question from a previous screen. The second column allows the user to select an operator applicable to the type of question asked. The third column allows the user to enter one or more values depending on the selected operator. Object Model public enum Operations { ... } public class Condition { int QuestionId { get; set; } Operations Operation { get; set; } List<object> Parameters { get; private set; } } List<Condition> pageSkipConditions; Controller Logic bool allConditionsTrue = pageSkipConditions.Count > 0; foreach (Condition c in pageSkipConditions) { allConditionsTrue &= Evaluate(previousAnswers, c); } // ... private bool Evaluate(List<Answers> previousAnswers, Condition c) { switch (c.Operation) { case Operations.StartsWith: // logic for this operation // etc. } }

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  • Extension objects pattern

    - by voroninp
    In this MSDN Magazine article Peter Vogel describes Extension Objects partten. What is not clear is whether extensions can be later implemented by client code residing in a separate assembly. And if so how in this case can extension get acces to private members of the objet being extended? I quite often need to set different access levels for different classes. Sometimes I really need that descendants does not have access to the mebmer but separate class does. (good old friend classes) Now I solve this in C# by exposing callback properties in interface of the external class and setting them with private methods. This also alows to adjust access: read only or read|write depending on the desired interface. class Parent { private int foo; public void AcceptExternal(IFoo external) { external.GetFooCallback = () => this.foo; } } interface IFoo { Func<int> GetFooCallback {get;set;} } Other way is to explicitly implement particular interface. But I suspect more aspproaches exist.

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  • Is there a factory pattern to prevent multiple instances for same object (instance that is Equal) good design?

    - by dsollen
    I have a number of objects storing state. There are essentially two types of fields. The ones that uniquely define what the object is (what node, what edge etc), and the others that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methods, so all these objects act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approach which accepts a Builder object and constructs the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquely defines the type of object (this is node A to node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows its state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overriding of serialization methods to make it work (ensure that when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in its place), as well as using a weakHashMap as if it was a weakHashSet to know whether an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to its own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state that is different than my memory; to tell my memory when its own state is inconsistent. I believe this is possible despite their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect that I'm posting).

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  • How to change the state of a singleton in runtime

    - by user34401
    Consider I am going to write a simple file based logger AppLogger to be used in my apps, ideally it should be a singleton so I can call it via public class AppLogger { public static String file = ".."; public void logToFile() { // Write to file } public static log(String s) { AppLogger.getInstance().logToFile(s); } } And to use it AppLogger::log("This is a log statement"); The problem is, what is the best time I should provide the value of file since it is a just a singleton? Or how to refactor the above code (or skip using singleton) so I can customize the log file path? (Assume I don't need to write to multiple at the same time) p.s. I know I can use library e.g. log4j, but consider it is just a design question, how to refactor the code above?

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  • Game State / Screen Management

    - by Ashylnn Mac
    What's the best way to handle game states / screens? My problem is this: PlayGameScreen adds a new InventoryGameScreen to the game during it's update. This immediately adds InventoryGameScreen to the array of GameScreens. That's throwing an exception when iterating over the array that the contents of the array have changed. Should I have two more arrays, like screensToBeAdded and screensToBeRemoved and do all the processing for them at the end of the game loop after drawing all the other screens?

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