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• A talk about observer pattern

  - by Martin

  As part of a university course I'm taking, I have to hold a 10 minute talk about the observer pattern. So far these are my points: What is it? (defenition) Polling is an alternative Polling VS Observer When Observer is better When Polling is better (taken from here) A statement that Mediator pattern is worth checking out. (I won't have time to cover it in 10 minutes) I would be happy to hear about: Any suggestions to add something? Another alternative (if exists)

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• Cluster Nodes as RAID Drives

  - by BuckWoody

  I'm unable to sleep tonight so I thought I would push this post out VERY early. When you don't sleep your mind takes interesting turns, which can be a good thing. I was watching a briefing today by a couple of friends as they were talking about various ways to arrange a Windows Server Cluster for SQL Server. I often see an "active" node of a cluster with a "passive" node backing it up. That means one node is working and accepting transactions, and the other is not doing any work but simply "standing by" waiting for the first to fail over. The configuration in the demonstration I saw was a bit different. In this example, there were three nodes that were actively working, and a fourth standing by for all three. I've put configurations like this one into place before, but as I was looking at their architecture diagram, it looked familar - it looked like a RAID drive setup! And that's not a bad way to think about your cluster arrangements. The same concerns you might think about for a particular RAID configuration provides a good way to think about protecting your systems in general. So even if you're not staying awake all night thinking about SQL Server clusters, take this post as an opportunity for "lateral thinking" - a way of combining in your mind the concepts from one piece of knowledge to another. You might find a new way of making your technical environment a little better. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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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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• What is the value in hiding the details through abstractions? Isn't there value in transparency?

  - by user606723

  Background I am not a big fan of abstraction. I will admit that one can benefit from adaptability, portability and re-usability of interfaces etc. There is real benefit there, and I don't wish to question that, so let's ignore it. There is the other major "benefit" of abstraction, which is to hide implementation logic and details from users of this abstraction. The argument is that you don't need to know the details, and that one should concentrate on their own logic at this point. Makes sense in theory. However, whenever I've been maintaining large enterprise applications, I always need to know more details. It becomes a huge hassle digging deeper and deeper into the abstraction at every turn just to find out exactly what something does; i.e. having to do "open declaration" about 12 times before finding the stored procedure used. This 'hide the details' mentality seems to just get in the way. I'm always wishing for more transparent interfaces and less abstraction. I can read high level source code and know what it does, but I'll never know how it does it, when how it does it, is what I really need to know. What's going on here? Has every system I've ever worked on just been badly designed (from this perspective at least)? My philosophy When I develop software, I feel like I try to follow a philosophy I feel is closely related to the ArchLinux philosophy: Arch Linux retains the inherent complexities of a GNU/Linux system, while keeping them well organized and transparent. Arch Linux developers and users believe that trying to hide the complexities of a system actually results in an even more complex system, and is therefore to be avoided. And therefore, I never try to hide complexity of my software behind abstraction layers. I try to abuse abstraction, not become a slave to it. Question at heart Is there real value in hiding the details? Aren't we sacrificing transparency? Isn't this transparency valuable?

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• Is it a "pattern smell" to put getters like "FullName" or "FormattedPhoneNumber" in your model?

  - by DanM

  I'm working on an ASP.NET MVC app, and I've been getting into the habit of putting what seem like helpful and convenient getters into my model/entity classes. For example: public class Member { public int Id { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public string PhoneNumber { get; set; } public string FullName { get { return FirstName + " " + LastName; } } public string FormattedPhoneNumber { get { return "(" + PhoneNumber.Substring(0, 3) + ") " + PhoneNumber.Substring(3, 3) + "-" + PhoneNumber.Substring(6); } } } I'm wondering people think about the FullName and FormattedPhoneNumber getters. They make it very easy to create standardized data formats throughout the app, and they seem to save a lot of repeated code, but it could definitely be argued that data format is something that should be handled in mapping from model to view-model. In fact, I was originally applying these data formats in my service layer where I do my mapping, but it was becoming a burden to constantly have to write formatters then apply them in many different places. E.g., I use "Full Name" in most views, and having to type something like model.FullName = MappingUtilities.GetFullName(entity.FirstName, entity.LastName); all over the place seemed a lot less elegant than just typing model.FullName = entity.FullName (or, if you use something like AutoMapper, potentially not typing anything at all). So, where do you draw the line when it comes to data formatting. Is it "okay" to do data formatting in your model or is that a "pattern smell"? Note: I definitely do not have any html in my model. I use html helpers for that. I'm strictly talking about formatting or combining data (and especially data that is frequently used).

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• Can an aggregate root hold references of members of another aggregate root?

  - by Rushino

  Hello, I know outside aggregates cant change anything inside an aggregate without passing by his root. That said i would like to know if an aggregate root can hold references of members (objects insides) of another aggregate root? (fellowing DDD rules) Example : a Calendar contain a list of phases which contain a list of sequences which contain a list of assignations Calendar is root because phases and sequences and assignations only work in context of a calendar. You also have Students and Groups of student (called groups) It is possible (fellowing DDD rules) to make Groups holding references of assignations or it need to pass by the root for accessing groups from assignations ? Thanks.

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• Using IComparable<T> Interface

  - by Pawan_Mishra

  Level : Beginner to Intermediate C# language has constantly evolved over a constant period of time.Each new version introduced new features which changed the way we programmed and solved the problems. Whether it was introduction of generics in C# 2.0 , LINQ in C# 3.0 or concept of dynamic programming in C# 4.0 , each of them had or will have greater impact on our programming style.As a developer we don’t have much option but to evolve and redefine our self in this constantly changing environment...(read more)

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• What are current Biggest Challenges faced by Ecommerce Applications ?

  - by Rachel

  I am in the process to start Product Development for E-commerce and Online Retail domain but before starting I would like to know what are the biggest challenges faced by current state of Art E-Commerce Application ? Also I have not experience building e-commerce products and so what things should I keep in mind before developing one ? Is there are books, articles, blogs outside which I should refer to gain some knowledge before starting out ? Update: What are you thoughts on the recommendation engines for ecommerce applications ? What challenges we have with current state of recommendations engines for ecommerce web application and how can we overcome them ?

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• C# XNA - Sky Sphere Question

  - by Wade

  I have been banging my head against the wall trying to get a sky sphere to work appropriately in XNA 4.0. I have the sphere loading correctly, and even textured, but i would like something a little more dynamic that can support a day/night cycle. My issue is that, while i know a good amount of C# and XNA, i know next to nothing about HLSL. (I could make an ambient light shader if my life depended on it...) I also have not been able to find a tutorial on how to build a sky sphere like this. Of course i don't expect to be able to make an amazing one right off the bat, i would like to start small, with a dynamic coloring sky i'll work out the clouds and sun later. My first question: Does anyone know of any good tutorial sites that could help me get a decent grasp around HLSL? Second: Does anyone have a good example of or know where to find one of a gradient sky using XNA and C#?

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• Multithreaded UI desktop application issues

  - by igor

  I am involved into development a rich UI project: desktop windows application. Application uses asynchronous invocations and in its turn it should be ready to process external messages (events). The problem is clear: at first time it was built as a simple prototype and it was not stress tested and all was fine. Then application was grown: the number of calls to server and number of events from server are high and performance is low. What is more users noticed that sometimes performance is extremal low. Asynchronous invocations based on thread pool (BeginInvoke, EndInvoke), external events are going from WCF service (.NET 3.5). My goal is synchronization of all tasks and putting priorities to every executions in desktop application. My question is: is there any practice how to reach my goal: patterns, task priority list, others? What should I do at first, second and next times? Thanks

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• Scene Graph Traversing Techniques

  - by Bunkai.Satori

  Scene Graph seems to be the most effective way of representing the game world. The game world usually tends to be as large as the memory and device can handle. In contrast, the screen of the device captures only a fraction of the Game World/Scene Graph. Ideally, I wish to process(update and render) only the visible game objects/nodes on per-frame basis. My question therefore is, how to traverse the scene graph so, that I will focus only on the game notes that are in the camera frustum? How to organize data so that I can easily focus only on the scene graph nodes visible to me? What are techniques to minimize scenegraph traversal time? Is there such way as more effective traversal, or do I have to traverse whole scene graph on per-frame basis?

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• Dapper and object validation/business rules enforcement

  - by Eugene

  This isn't really Dapper-specific, actually, as it relates to any XML-serializeable object.. but it came up when I was storing an object using Dapper. Anyways, say I have a user class. Normally, I'd do something like this: class User { public string SIN {get; private set;} public string DisplayName {get;set;} public User(string sin) { if (string.IsNullOrWhiteSpace(sin)) throw new ArgumentException("SIN must be specified"); this.SIN = sin; } } Since a SIN is required, I'd just create a constructor with a sin parameter, and make it read-only. However, with a Dapper (and probably any other ORM), I need to provide a parameterless constructor, and make all properties writeable. So now I have this: class User: IValidatableObject { public int Id { get; set; } public string SIN { get; set; } public string DisplayName { get; set; } public IEnumerable<ValidationResult> Validate(ValidationContext validationContext) { // implementation } } This seems.. can't really pick the word, a bad smell? A) I'm allowing to change properties that should not be changed ever after an object has been created (SIN, userid) B) Now I have to implement IValidatableObject or something like that to test those properties before updating them to db. So how do you go about it ?

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• Beginning with first project on game development [closed]

  - by Tsvetan

  Today is the day I am going to start my first real game project. It will be a Universe simulator. Basically, you can build anything from tiny meteor to quazars and universes. It is going to be my project for an olympiad in IT in my country and I really want to make it perfect(at least a bronze medal). So, I would like to ask some questions about organization and development methodologies. Firstly, my plan is to make a time schedule. In it I would write my plans for the next month or two(because that is the time I have). With this exact plan I hope to make my organisation at its best. Of course, if I am doing sth faster than the schedule I would involve more features for the game and/or continue with the tempo I have. Also, for the organisation I would make a basic pseudocode(maybe) and just rewrite it so it is compilable. Like a basic skeleton of everything. The last is an idea I tought of in the moment, but if it is good I will use it. Secondly, for the development methodologies, obviously, I think of making object-oriented code and make everything perfect(a lot of testing, good code, documentation etc.). Also, I am going to make my own menu system(I read that OpenGL hasn't got very good one). Maybe I would implement it with an xml file, holding the info about position of buttons, text boxes, images and everything. Maybe I would do a specific CSS for it and so on. I think that is very good way of doing the menu system, because it makes the presentation layer separate of the logic. But, if there is a better way, I would do it the better way. For the logic, well, I don't have much to say. OO code, testing, debuging, good and fast algorithms and so on. Also, a good documentation must be written and this is the area I need to make some research in. I think that is for now. I hope I have been enough descriptive. If more questions come on my mind, I will ask them. Edit: I think of blogging every part of the project, or at least writing down everything in a file or something like that. My question is: Is my plan of how to do everything around the project good? And if not, what is necessary to be improved and what other things I can involve for making the project good.

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• What's wrong with JavaScript

  - by ts01

  There is a lot of buzz around Dart recently, often questioning Google motivations and utility of Dart as replacement for JavaScript. I was searching for rationale of creating Dart rather than investing more effort in ECMAScript. In well known leaked mail its author is saying that Javascript has historical baggage that cannot be solved without a clean break. But there is only one concrete example given (apart of performance concerns) of "fundamental language problems", which is an existence of a single Number primitive So, my questions are: How an existence of a single Number primitive can be a "fundamental problem"? Are there other known "fundamental problems" in JavaScript?

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• Advantages of Singleton Class over Static Class?

  Point 1)Singleton We can get the object of singleton and then pass to other methods.Static Class We can not pass static class to other methods as we pass objectsPoint 2) Singleton In future, it is easy to change the logic of of creating objects to some pooling mechanism. Static Class Very difficult to implement some pooling logic in case of static class. We would need to make that class as non-static and then make all the methods non-static methods, So entire your code needs to be changed.Point3:) Singleton Can Singletone class be inherited to subclass? Singleton class does not say any restriction of Inheritence. So we should be able to do this as long as subclass is also inheritence.There's nothing fundamentally wrong with subclassing a class that is intended to be a singleton. There are many reasons you might want to do it. and there are many ways to accomplish it. It depends on language you use.Static Class We can not inherit Static class to another Static class in C#. Think about it this way: you access static members via type name, like this: MyStaticType.MyStaticMember(); Were you to inherit from that class, you would have to access it via the new type name: MyNewType.MyStaticMember(); Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism. span.fullpost {display:none;}

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• Factors to consider when building an algorithm for gun recoil

  - by Nate Bross

  What would be a good algorithm for calculating the recoil of a shooting guns cross-hairs? What I've got now, is something like this: Define min/max recoil based on weapon size Generate random number of "delta" movement Apply random value to X, Y, or both of cross-hairs (only "up" on the Y axis) Multiply new delta based on time from the previous shot (more recoil for full-auto) What I'm worried about is that this feels rather predicable, what other factors should one take into account when building recoil? While I'd like it to be somewhat predictable, I'd also like to keep players on their toes. I'm thinking about increasing the min/max recoil values by a large amount (relatively) and adding a weighting, so large recoils will be more rare -- it seems like a lot of effort to go into something I felt would be simple. Maybe this is just something that needs to be fine-tuned with additional playtesting, and more playtesters? I think that it's important to note, that the recoil will be a large part of the game, and is a key factor in the game being fun/challenging or not.

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• How to document/verify consistent layering?

  - by Morten

  I have recently moved to the dark side: I am now a CUSTOMER of software development -- mainly websites. With this new role comes new concerns. As a programmer i know how solid an application becomes when it is properly layered, and I want to use this knowledge in my new job. I don't want business logic in my presentation layer, and certainly not presentation stuff in my data layer. Thus, I want to be able to demand from my supllier that they document the level of layering, and how neat and consistent the layering is. The big question is: How is the level of layering documented to me as a customer, and is that a reasonable demmand for me to have, so I don't have to look in the code (I'm not supposed to do that anymore)?

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• Multithreded UI desktop application issues

  - by igor

  I am involved into development a rich UI project: desktop windows application. Application uses asynchronous invocations and in its turn it should be ready to process external messages (events). The problem is clear: at first time it was built as a simple prototype and it was not stress tested and all was fine. Then application was grown: the number of calls to server and number of events from server are high and performance is low. What is more users noticed that sometimes performance is extremal low. Asynchronous invocations based on thread pool (BeginInvoke, EndInvoke), external events are going from WCF service (.NET 3.5). My goal is synchronization of all tasks and putting priorities to every executions in desktop application. My question is: is there any practice how to reach my goal: patterns, task priority list, others? What should I do at first, second and next times? Thanks

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• What are the downsides to using dependency injection?

  - by kerry

  I recently came across an interesting question on stack overflow with some interesting reponses.  I like this post for three reasons. First, I am a big fan of dependency injection, it forces you to decouple your code, create cohesive interfaces, and should result in testable classes. Second, the author took the approach I usually do when trying to evaluate a technique or technology; suspend personal feelings and try to find some compelling arguments against it. Third, it proved that it is very difficult to come up with a compelling argument against dependency injection. What are the downsides to using dependency injection?

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• Using virtual functions

  - by Tucker Morgan

  I am starting to use virtual functions, and i am programming a simple text game, my question is this, if i have a virtual function called spec_abil with in a Super class called rpg_class. If you allow the player to class what class they want to play, say a mage class, a archer class, and a warrior class, which all have their own spec_abil function. How do you write it so that the program knows which one to use depending on the chosen class.

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• NCurses, scrolling of multiline items, "current item" pointer and "selected items"

  - by mjf

  I am looking for hints/ideas for the best (most effective) way on how to scroll multi-line items as well as emphasizing of the "current item" and "selected items" such as: 1 FOO ITEM 1 Foo sub-item 2 Foo sub-item 3 Foo sub-item 2 BAR ITEM 1 Bar sub-item 3 BAZ ITEM 1 Baz sub-item 2 Baz sub-item 4 RAB ITEM 5 ZZZ ITEM 1 Zzz sub-item 2 Zzz sub-item 3 Zzz sub-item 4 Zzz sub-item using NCurses (some combination of windows, sub-windows, pads, copywin? Uff! In fact, the lines could exceed the stdscr's width so that possibility to scroll left/right would be also nice - pads?)... The whole items (including the sub-items) are supposed to be emphasized as full-width window/pad areas. The "current item" (including it's set of lines) should be emphasized (i.e. using A_BOLD), selected set of items of choice (including the set of lines for each the selected item) should be emphasized in another way (i.e. using A_REVERSE). What would you choose to cope with it the most effective NCurses way? (The less redrawals/refreshes the better and terminal is supposed to have the ability to change it's size - such as XTerm running under "floating window" management.) Thank you for your ideas (or perhaps some piece of code where something similar is already solved - I was not able to find anything helpful on the Internet. I mean I am not going to copy/paste foreign code but programming NCurses properly is still somehow difficult to me). P.S.: Would you suggest to "smooth-scroll" +1/-1 screen line or rather "jump-scroll" +lines/-lines of the items? (I personally prefer the latter one.) Sincerely, -- mjf

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• Evolution of an Application: how to manage and improve core engine?

  - by Phil Carter

  The web application I work on has been live for a year now, but it's time for it to evolve and one of the ways in which it is evolving is into a multi-brand application - in this case several different companies using the application, different templates/content and some slight business logic changes between them. The problem I'm facing is implementing a best practice across the site where there are differences in business logic for each brand. These will mostly be very superficial, using a an alternative mailing list provider or capturing some extra data in a form. I don't want to have if(brand === x) { ... } else { ... } all over the site especially as most of what needs to be changed can be handled with extending the existing class. I've thought of several methods that could be used to instantiate the correct class, but I'm just not sure which is going to be best especially as some seem to lead to duplication of more code than should be necessary. Here's what I've considered: 1) Use a Static Loader similar to Zend_Loader which can take the class being requested, and has knowledge of the Brand and can then return the correct object. $class = App_Loader::getObject('User', $brand); 2) Factory classes. We use these in the application already for Products but we could utilise them here also to provide a transparent interface to the class. 3) Routing the page request to a specific brand controller. This however seems like it would duplicate a lot of code/logic. Is there a pattern or something else I should be considering to solve this problem? 4) How to manage a growing project that has multiple custom instances in production? Update This is a PHP application so the decisions on which class to load are made per request. There could be upwards of 100+ different 'brands' running.

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• Architecture for Social Graph data that has a Time Frame Associated?

  - by Jay Stevens

  I am adding some "social" type features to an existing application. There are a limited # of node & edge types. Overall the data itself is relatively small (50,000 - 70,000 for each type of node) there will be a number of edges (relationships) between them (almost all directional). This, I know, is relatively easy to represent with an SDF store (such as BrightstarDB) or something like Microsoft's Trinity (or really many of the noSQL options). The thing that, I think, makes this a unique use case is that each relationship will have a timeframe associated with it (start and end dates). Right now, I'm thinking of just storing this in a relational structure and dealing with the headaches of "traversing the graph", but I'm looking for suggestions on a better approach (both in terms of data structure and server): Column ================ From_Node_ID Relationship To_Node_ID StartDate EndDate Any suggestions or thoughts are welcomed.

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• Securing iOS or Android Backend API

  - by El Guapo

  I have an application that I am writing for both iOS and Android; this application will be served by a ReSTFUL API running on a cluster of servers on "the internets". I am curious how the rest of the world is going about securing their APIs so only specific applications running on iOS or Android can use these APIs. I could go the same route as other OAuth providers by providing a key/secret combination (2-legged OAuth), however, what do I do if I ever have to change these keys??? Do I create a new key/secret for every person that downloads the app???

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• Please recommend a patterns book for iOS development

  - by Brett Ryan

  I've read several books on iOS development and Objective-C, however what a lot of them teach is how to work with interfaces and all contain the model inside the view controller, i.e. a UITableViewController based view will simply have an NSArray as it's model. I'm interested in what the best practices are for designing the structure of an application. Specifically I'm interested in best practices for the following: How to separate a model from the view controller. I think I know how to do this by simply replacing the NSArray style example with a specific model object, however what I do not know how to do is alert the view when the model changes. For example in .NET I would solve this by conforming to INotifyPropertyChanged and databinding, and similarly with Java I would use PropertyChangeListener. How to create a service model for my domain objects. For example I want to learn the best way to create a service for a hypothetical Widget object to manage an internal DB and also services for communicating with remote endpoints. I need to learn the best ways to do this in a way that interface components can subscribe to events such as widgetUpdated. These services should be singleton classes and some how dependency injected into model/controller objects. Books I've read so far are: Programming in Objective-C (4th Edition) Beginning iOS 5 Development: Exploring the iOS SDK The iOS 5 Developer's Cookbook: Expanded Electronic Edition: Essentials and Advanced Recipes for iOS Programmers Learn Objective-C on the Mac: For OS X and iOS I've also purchased the following updated books but not yet read them. The Core iOS 6 Developer's Cookbook (4th edition Programming in Objective-C (5th Edition) I come from a Java and C# background with 15 years experience, I understand that many of the ways I would do things in these languages may not fit to the ObjC way of developing applications. Any guidance on the topic is very much appreciated.

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