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  • SQL Analysis Services - Dimension attributes with a "many" cardinality

    - by MonkeyBrother
    I am creating a cube with the following tables: Customer CustomerID, Name Customer Rep CustomerID, RepID Rep RepID, Name The important thing here is that there is a many to many relationship between Reps and Customers. I want to be able to ask the question "How much sales for customers working with rep 'A'?" In the data source view i set up the relationships between both customerid columns and both repid columns. I set up the rep attribute in the dimension builder and when I try to build the cube I get this error: Errors in the high-level relationship engine. the 'Rep' table that is required for a join cannot be reached based on the relationships in the data source view.

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  • Make sure bad patterns don't come back after refactoring

    - by Let_Me_Be
    I'm refactoring an old C code. The code has absolutely no layered architecture (everything is being accessed by everything) and I'm trying to change that. I would like to cut direct access to structure members (at least write for now) and only allow access through access functions. Is there some tool (or perhaps directly the compiler) that could check this rule for me? I need this since I'm maintaining a fork and the upstream isn't very concerned with code quality.

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  • Integration Patterns with Azure Service Bus Relay, Part 3.5: Node.js relay

    - by Elton Stoneman
    This is an extension to Part 3 in the IPASBR series, see also: Integration Patterns with Azure Service Bus Relay, Part 1: Exposing the on-premise service Integration Patterns with Azure Service Bus Relay, Part 2: Anonymous full-trust .NET consumer Integration Patterns with Azure Service Bus Relay, Part 3: Anonymous partial-trust consumer In Part 3 I said “there isn't actually a .NET requirement here”, and this post just follows up on that statement. In Part 3 we had an ASP.NET MVC Website making a REST call to an Azure Service Bus service; to show that the REST stuff is really interoperable, in this version we use Node.js to make the secure service call. The code is on GitHub here: IPASBR Part 3.5. The sample code is simpler than Part 3 - rather than code up a UI in Node.js, the sample just relays the REST service call out to Azure. The steps are the same as Part 3: REST call to ACS with the service identity credentials, which returns an SWT; REST call to Azure Service Bus Relay, presenting the SWT; request gets relayed to the on-premise service. In Node.js the authentication step looks like this: var options = { host: acs.namespace() + '-sb.accesscontrol.windows.net', path: '/WRAPv0.9/', method: 'POST' }; var values = { wrap_name: acs.issuerName(), wrap_password: acs.issuerSecret(), wrap_scope: 'http://' + acs.namespace() + '.servicebus.windows.net/' }; var req = https.request(options, function (res) { console.log("statusCode: ", res.statusCode); console.log("headers: ", res.headers); res.on('data', function (d) { var token = qs.parse(d.toString('utf8')); callback(token.wrap_access_token); }); }); req.write(qs.stringify(values)); req.end(); Once we have the token, we can wrap it up into an Authorization header and pass it to the Service Bus call: token = 'WRAP access_token=\"' + swt + '\"'; //... var reqHeaders = { Authorization: token }; var options = { host: acs.namespace() + '.servicebus.windows.net', path: '/rest/reverse?string=' + requestUrl.query.string, headers: reqHeaders }; var req = https.request(options, function (res) { console.log("statusCode: ", res.statusCode); console.log("headers: ", res.headers); response.writeHead(res.statusCode, res.headers); res.on('data', function (d) { var reversed = d.toString('utf8') console.log('svc returned: ' + d.toString('utf8')); response.end(reversed); }); }); req.end(); Running the sample Usual routine to add your own Azure details into Solution Items\AzureConnectionDetails.xml and “Run Custom Tool” on the .tt files. Build and you should be able to navigate to the on-premise service at http://localhost/Sixeyed.Ipasbr.Services/FormatService.svc/rest/reverse?string=abc123 and get a string response, going to the service direct. Install Node.js (v0.8.14 at time of writing), run FormatServiceRelay.cmd, navigate to http://localhost:8013/reverse?string=abc123, and you should get exactly the same response but through Node.js, via Azure Service Bus Relay to your on-premise service. The console logs the WRAP token returned from ACS and the response from Azure Service Bus Relay which it forwards:

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  • Is this an acceptable UI design decision?

    - by DVK
    OK, while I'm on record as stating that StackExchange UI is pretty much one of the best websites and overall GUIs that I have ever seen as far as usability goes, there's one particular aspect of the trilogy that bugs me. For an example, head on to http://meta.stackoverflow.com . Look at the banner on top (the one that says "reminder -- it's April Fool's Day depending on your time zone!"). Personally, I feel that this is a "make the user do the figuring out work" anti-pattern (whatever it's officially called) - namely, instead of making your app smart enough to only present a certain mode of operations in the conditions when that mode is appropriate, you simply turn on the mode full on and put an explanation to the user of why the mode is on when it should not be (in this particular example, the mode is of course displaying the unicorn gravatars starting with 00:00 in the first timezone, despite the fact that some users still live in March 31st). The Great Recalc was also handled the same way - instead of proactively telling the user "your rep was changed from X to Y" the same nearly invisible banner was displayed on meta. So, the questions are: Is there such an official anti-pattern, and if so,m what the heck do i call it? Do you have any other well-known examples of such design anti-pattern? How would you fix either the SO example I made or you your own example? Is there a pattern of fixing or must it be a case-by-case solution?

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  • C#: How to resolve this circular dependency?

    - by Rosarch
    I have a circular dependency in my code, and I'm not sure how to resolve it. I am developing a game. A NPC has three components, responsible for thinking, sensing, and acting. These components need access to the NPC controller to get access to its model, but the controller needs these components to do anything. Thus, both take each other as arguments in their constructors. ISenseNPC sense = new DefaultSenseNPC(controller, worldQueryEngine); IThinkNPC think = new DefaultThinkNPC(sense); IActNPC act = new DefaultActNPC(combatEngine, sense, controller); controller = new ControllerNPC(act, think); (The above example has the parameter simplified a bit.) Without act and think, controller can't do anything, so I don't want to allow it to be initialized without them. The reverse is basically true as well. What should I do? ControllerNPC using think and act to update its state in the world: public class ControllerNPC { // ... public override void Update(long tick) { // ... act.UpdateFromBehavior(CurrentBehavior, tick); CurrentBehavior = think.TransitionState(CurrentBehavior, tick); } // ... } DefaultSenseNPC using controller to determine if it's colliding with anything: public class DefaultSenseNPC { // ... public bool IsCollidingWithTarget() { return worldQuery.IsColliding(controller, model.Target); } // ... }

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  • AntFarm anti-pattern -- strategies to avoid, antidotes to help heal from

    - by alchemical
    I'm working on a 10 page web site with a database back-end. There are 500+ objects in use, trying to implement the MVP pattern in ASP.Net. I'm tracing the code-execution from a single-page, my finger has been on F-11 in Visual Studio for about 40 minutes, there seems to be no end, possibly 1000+ method calls for one web page! If it was just 50 objects that would be one thing, however, code execution snakes through all these objects just like millions of ants frantically woring in their giant dirt mound house, riddled with object tunnels. Hence, a new anti-pattern is born : AntFarm. AntFarm is also known as "OO-Madnes", "OO-Fever", OO-ADD, or simply design-pattern junkie. This is not the first time I've seen this, nor my associates at other companies. It seems that this style is being actively propogated, or in any case is a misunderstanding of the numerous OO/DP gospels going around... I'd like to introduce an anti-pattern to the anti-pattern: GST or "Get Stuff Done" AKA "Get Sh** done" AKA GRD (GetRDone). This pattern focused on just what it says, getting stuff done, in a simple way. I may try to outline it more in a later post, or please share your ideas on this antidote pattern. Anyway, I'm in the midst of a great example of AntFarm anti-pattern as I write (as a bonus, there is no documentation or comments). Please share you thoughts on how this anti-pattern has become so prevelant, how we can avoid it, and how can one undo or deal with this pattern in a live system one must work with!

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  • When is lazy evaluation not useful?

    - by Cherian
    Delay execution is almost always a boon. But then there are cases when it’s a problem and you resort to “fetch” (in Nhibernate) to eager fetch it. Do you know practical situations when lazy evaluation can bite you back…?

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  • Can the Diamond Problem be really solved?

    - by Mecki
    A typical problem in OO programming is the diamond problem. I have parent class A with two sub-classes B and C. A has an abstract method, B and C implement it. Now I have a sub-class D, that inherits of B and C. The diamond problem is now, what implementation shall D use, the one of B or the one of C? People claim Java knows no diamond problem. I can only have multiple inheritance with interfaces and since they have no implementation, I have no diamond problem. Is this really true? I don't think so. See below: [removed vehicle example] Is a diamond problem always the cause of bad class design and something neither programmer nor compiler needs to solve, because it shouldn't exist in the first place? Update: Maybe my example was poorly chosen. See this image Of course you can make Person virtual in C++ and thus you will only have one instance of person in memory, but the real problem persists IMHO. How would you implement getDepartment() for GradTeachingFellow? Consider, he might be student in one department and teach in another one. So you can either return one department or the other one; there is no perfect solution to the problem and the fact that no implementation might be inherited (e.g. Student and Teacher could both be interfaces) doesn't seem to solve the problem to me.

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  • Analysis Services with excel as front end - is it possible to get the nicer UI that powerpivot provi

    - by AJM
    I have been looking into PowerPivot and concluded that for "self service BI" and ahoc buidling of cubes it has its uses. In particular I like the enhanced UI that you get from using PowerPivot rather than just using a PivotTable hooked up to an analysis services datasource. However it seems that hooking up PowerPivot to an existing analysis services cube is not a solution for "organisational BI". It is not always desireable to suck millions of rows into excel at once and the interface between PowerPivot and analysis services is very poor in my book. Hence the question is can an existing analysis services solution get the enhanced ui features that power pivot brings, withoout using powerpivot as the design tool? If powerpivot is aimed ad self service/personal BI then it seems bizare that the UI for this is better than for bigger/more costly analysis services solutions.

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  • Initialization of components with interdependencies - possible antipattern?

    - by Rosarch
    I'm writing a game that has many components. Many of these are dependent upon one another. When creating them, I often get into catch-22 situations like "WorldState's constructor requires a PathPlanner, but PathPlanner's constructor requires WorldState." Originally, this was less of a problem, because references to everything needed were kept around in GameEngine, and GameEngine was passed around to everything. But I didn't like the feel of that, because it felt like we were giving too much access to different components, making it harder to enforce boundaries. Here is the problematic code: /// <summary> /// Constructor to create a new instance of our game. /// </summary> public GameEngine() { graphics = new GraphicsDeviceManager(this); Components.Add(new GamerServicesComponent(this)); //Sets dimensions of the game window graphics.PreferredBackBufferWidth = 800; graphics.PreferredBackBufferHeight = 600; graphics.ApplyChanges(); IsMouseVisible = true; screenManager = new ScreenManager(this); //Adds ScreenManager as a component, making all of its calls done automatically Components.Add(screenManager); // Tell the program to load all files relative to the "Content" directory. Assets = new CachedContentLoader(this, "Content"); inputReader = new UserInputReader(Constants.DEFAULT_KEY_MAPPING); collisionRecorder = new CollisionRecorder(); WorldState = new WorldState(new ReadWriteXML(), Constants.CONFIG_URI, this, contactReporter); worldQueryUtils = new WorldQueryUtils(worldQuery, WorldState.PhysicsWorld); ContactReporter contactReporter = new ContactReporter(collisionRecorder, worldQuery, worldQueryUtils); gameObjectManager = new GameObjectManager(WorldState, assets, inputReader, pathPlanner); worldQuery = new DefaultWorldQueryEngine(collisionRecorder, gameObjectManager.Controllers); gameObjectManager.WorldQueryEngine = worldQuery; pathPlanner = new PathPlanner(this, worldQueryUtils, WorldQuery); gameObjectManager.PathPlanner = pathPlanner; combatEngine = new CombatEngine(worldQuery, new Random()); } Here is an excerpt of the above that's problematic: gameObjectManager = new GameObjectManager(WorldState, assets, inputReader, pathPlanner); worldQuery = new DefaultWorldQueryEngine(collisionRecorder, gameObjectManager.Controllers); gameObjectManager.WorldQueryEngine = worldQuery; I hope that no one ever forgets that setting of gameObjectManager.WorldQueryEngine, or else it will fail. Here is the problem: gameObjectManager needs a WorldQuery, and WorldQuery needs a property of gameObjectManager. What can I do about this? Have I found an anti-pattern?

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  • C# unusual inheritance syntax w/ generics

    - by anon
    I happened upon this in an NHibernate class definition: public class SQLiteConfiguration : PersistenceConfiguration<SQLiteConfiguration> So this class inherits from a base class that is parameterized by... the derived class?   My head just exploded. Can someone explain what this means and how this pattern is useful? (This is NOT an NHibernate-specific question, by the way.)

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  • How to use a 3rd party control inside the viewmodel?

    - by Sander
    I have a 3rd party control which among other things performs loading of some data. I want my viewmodel to keep track of this load operation and adjust its own state accordingly. If it were up to me, I'd do the data loading far away from the view, but it is not. So, I seem to be in the situation where my viewmodel depends on my view. How do I best handle this? I feel rather dirty making the view publish events to the viewmodel but I don't see any other reasonable way to get this info into the viewmodel. A similar situation might crop up with standard controls, too - imagine if your viewmodel depends on the events coming from a MediaElement - how do you properly model this? Do you put the MediaElement into the viewmodel? That doesn't sound right. If publishing the events to the viewmodel is indeed the most reasonable way, is there some common pattern used for this? How do you do it?

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  • Repository Design Pattern Guidance

    - by thefactor
    Let's say you have an MVVM CRM application. You have a number of customer objects in memory, through a repository. What would be the appropriate place to handle tasks that aren't associated with traditional MVVM tasks from a GUI? For example, let's say every few minutes you want to check to see if their address is valid and pop up a notification if it is not. Or you want to send out an hourly e-mail update. Or you want a window to pop up to remind you to call a customer at a specific time. Where does this logic go? It's not GUI/action-oriented, and it's not logic that would be appropriate for a repository, I think.

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  • Domain-Driven-Design question

    - by Michael
    Hello everyone, I have a question about DDD. I'm building a application to learn DDD and I have a question about layering. I have an application that works like this: UI layer calls = Application Layer - Domain Layer - Database Here is a small example of how the code looks: //****************UI LAYER************************ //Uses Ioc to get the service from the factory. //This factory would be in the MyApp.Infrastructure.dll IImplementationFactory factory = new ImplementationFactory(); //Interface and implementation for Shopping Cart service would be in MyApp.ApplicationLayer.dll IShoppingCartService service = factory.GetImplementationFactory<IShoppingCartService>(); //This is the UI layer, //Calling into Application Layer //to get the shopping cart for a user. //Interface for IShoppingCart would be in MyApp.ApplicationLayer.dll //and implementation for IShoppingCart would be in MyApp.Model. IShoppingCart shoppingCart = service.GetShoppingCartByUserName(userName); //Show shopping cart information. //For example, items bought, price, taxes..etc ... //Pressed Purchase button, so even for when //button is pressed. //Uses Ioc to get the service from the factory again. IImplementationFactory factory = new ImplementationFactory(); IShoppingCartService service = factory.GetImplementationFactory<IShoppingCartService>(); service.Purchase(shoppingCart); //**********************Application Layer********************** public class ShoppingCartService : IShoppingCartService { public IShoppingCart GetShoppingCartByUserName(string userName) { //Uses Ioc to get the service from the factory. //This factory would be in the MyApp.Infrastructure.dll IImplementationFactory factory = new ImplementationFactory(); //Interface for repository would be in MyApp.Infrastructure.dll //but implementation would by in MyApp.Model.dll IShoppingCartRepository repository = factory.GetImplementationFactory<IShoppingCartRepository>(); IShoppingCart shoppingCart = repository.GetShoppingCartByUserName(username); //Do shopping cart logic like calculating taxes and stuff //I would put these in services but not sure? ... return shoppingCart; } public void Purchase(IShoppingCart shoppingCart) { //Do Purchase logic and calling out to repository ... } } I've seem to put most of my business rules in services rather than the models and I'm not sure if this is correct? Also, i'm not completely sure if I have the laying correct? Do I have the right pieces in the correct place? Also should my models leave my domain model? In general I'm I doing this correct according DDD? Thanks!

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  • How to see "anti if" movement and its gaol?

    - by Vijay Shanker
    I have a developer for last 3 years, have been using if-else or if-else if statements a lot in my programing habit. And today, I found This link. One obvious sample i put here public void doSomthing(String target, String object){ //validate requests if(target != null && target.trim().length() < 1){ //invalid request; } //further logic } Now, I have seen this sort of check all over the places, libraries. So, I wanted to have a discussion about the worthiness of such a movement. Please let me know your views.

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  • How to make 2 incompatible types, but with the same members, interchangeable?

    - by Quigrim
    Yesterday 2 of the guys on our team came to me with an uncommon problem. We are using a third-party component in one of our winforms applications. All the code has already been written against it. They then wanted to incorporate another third-party component, by the same vender, into our application. To their delight they found that the second component had the exact same public members as the first. But to their dismay, the 2 components have completely separate inheritance hierarchies, and implement no common interfaces. Makes you wonder... Well, makes me wonder. An example of the problem: public class ThirdPartyClass1 { public string Name { get { return "ThirdPartyClass1"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass1 is doing its thing."); } } public class ThirdPartyClass2 { public string Name { get { return "ThirdPartyClass2"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass2 is doing its thing."); } } Gladly they felt copying and pasting the code they wrote for the first component was not the correct answer. So they were thinking of assigning the component instant into an object reference and then modifying the code to do conditional casts after checking what type it was. But that is arguably even uglier than the copy and paste approach. So they then asked me if I can write some reflection code to access the properties and call the methods off the two different object types since we know what they are, and they are exactly the same. But my first thought was that there goes the elegance. I figure there has to be a better, graceful solution to this problem.

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  • Specify a custom dictionary for FxCop and Visual Studio source analysis

    - by Marko Apfel
    Renaming the default custom dictionary from CustomDictionary.xml to an other name – for instance FxCop.CustomDictionary.xml needs some additional changes to work in involved applications. Visual Studio Team System code analysis For Visual Studio Team System code analysis this file should be added as a link to all projects and setted to be the Build Action CodeAnalysisDirectory. Build target In a build target the command line tool FxCopCmd should be called with the /dictionary parameter: <Target Name="FxCop"> <Exec Command="&quot;$(ProjectDir)..\..\build\FxCop\FxCopCmd.exe&quot; /file:&quot;$(TargetPath)&quot; /project:&quot;$(ProjectDir)..\EsriDE.SfgPraxair.FxCop&quot; /directory:&quot;$(ProjectDir)..\..\lib\Esri.ArcGIS&quot; /directory:&quot;$(ProjectDir)..\..\lib\Microsoft&quot; /dictionary:&quot;$(ProjectDir)..\FxCop.CustomDictionary.xml&quot; /out:&quot;$(OutDir)..\$(ProjectName).FxCopReport.xml&quot; /console /forceoutput /ignoregeneratedcode"> </Exec> <Message Text="FxCop finished." /> </Target> FxCop-GUI (standalone application) In FxCop-GUI is no option to specify an own file name – but you could add a hint in the FxCop project file. Open your this file and look for the line: <CustomDictionaries SearchFxCopDir="True" SearchUserProfile="True" SearchProjectDir="True" /> Then change it to: <CustomDictionaries SearchFxCopDir="True" SearchUserProfile="True" SearchProjectDir="True"> <CustomDictionary Path="FxCop.CustomDictionary.xml"/> </CustomDictionaries> Ready :-)

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  • Great Example of a Simple Cost-Benefit Analysis

    - by BuckWoody
    I saw a post the other day that you should definitely go check out. It’s a cost/benefit decision, and although the author gives it a quick treatment and doesn’t take all points in the decision into account, you should focus on the process he follows. It’s a quick and simple example of the kind of thought process we should have as data professionals when we pick a server, a process, or application and even platform software. The key is to include more than just the price of a piece of software or hardware. You need to think about the “other” costs in the decision, and then make the right one. Sometimes the cheapest option is the cheapest, and other times, well, it isn’t. I’ve seen this played out not only in the decision to go with a certain selection, but in the options or editions it comes in. You have to put all of the decision points in the analysis to come up with the right answer, and you have to be able to explain your logic to your team and your company. This is the way you become a data professional, not just a DBA. You can check out the post here – it deals with Azure, but the point is the process, not Azure itself: http://blogs.msdn.com/eugeniop/archive/2010/03/19/windows-azure-guidance-a-simplistic-economic-analysis-of-a-expense-migration.aspx Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Master Data Management – A Foundation for Big Data Analysis

    - by Manouj Tahiliani
    While Master Data Management has crossed the proverbial chasm and is on its way to becoming mainstream, businesses are being hammered by a new megatrend called Big Data. Big Data is characterized by massive volumes, its high frequency, the variety of less structured data sources such as email, sensors, smart meters, social networks, and Weblogs, and the need to analyze vast amounts of data to determine value to improve upon management decisions. Businesses that have embraced MDM to get a single, enriched and unified view of Master data by resolving semantic discrepancies and augmenting the explicit master data information from within the enterprise with implicit data from outside the enterprise like social profiles will have a leg up in embracing Big Data solutions. This is especially true for large and medium-sized businesses in industries like Retail, Communications, Financial Services, etc that would find it very challenging to get comprehensive analytical coverage and derive long-term success without resolving the limitations of the heterogeneous topology that leads to disparate, fragmented and incomplete master data. For analytical success from Big Data or in other words ROI from Big Data Investments, businesses need to acquire, organize and analyze the deluge of data to make better decisions. There will need to be a coexistence of structured and unstructured data and to maintain a tight link between the two to extract maximum insights. MDM is the catalyst that helps maintain that tight linkage by providing an understanding about the identity, characteristics of Persons, Companies, Products, Suppliers, etc. associated with the Big Data and thereby help accelerate ROI. In my next post I will discuss about patterns for co-existing Big Data Solutions and MDM. Feel free to provide comments and thoughts on above as well as Integration or Architectural patterns.

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  • How to Effectively Create Bullet Patterns

    - by SoulBeaver
    I'm currently creating a top-down shooter like Touhou. The most important factor of the game is that there are many diverse patterns and ways at which bullets are generated and shot at the player, see this video: http://www.youtube.com/watch?v=4Nb5Ohbt1Sg#start=0:60;end=9:53; At the moment, I'm using a class "Pattern" which has a series of steps on moving and shooting. However, I feel this method is quite laborous as I have to create a new Pattern for each attack and perhaps new Bullet classes that will implement a certain behavior. This question received a comment suggesting I should look into BulletML for easy creation and storage of bullets with a specific pattern. It looks decent, but it led me to wonder, what other solutions do you have that I should take into consideration? Update My current design is as follows: An example of an implemented pattern: My GigasPattern first executes a teleport which moves Alice to a certain point (X, Y) on the screen. After this is completed, the pattern starts using the Mover to move the sprite around (whereas teleporting has separate effects and animation). These are of no concern, really, as they are quite simple. The Shooter also creates various Attacks, which are classes again that the Shooter can use to create various patterns of bullets, much like the one in the question I posted. Once the Mover has reached it's destination, both it and the shooter stop and return to an inactive state. The pattern completes, is removed by the AI and a new one gets chosen.

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  • JavaScript Class Patterns

    - by Liam McLennan
    To write object-oriented programs we need objects, and likely lots of them. JavaScript makes it easy to create objects: var liam = { name: "Liam", age: Number.MAX_VALUE }; But JavaScript does not provide an easy way to create similar objects. Most object-oriented languages include the idea of a class, which is a template for creating objects of the same type. From one class many similar objects can be instantiated. Many patterns have been proposed to address the absence of a class concept in JavaScript. This post will compare and contrast the most significant of them. Simple Constructor Functions Classes may be missing but JavaScript does support special constructor functions. By prefixing a call to a constructor function with the ‘new’ keyword we can tell the JavaScript runtime that we want the function to behave like a constructor and instantiate a new object containing the members defined by that function. Within a constructor function the ‘this’ keyword references the new object being created -  so a basic constructor function might be: function Person(name, age) { this.name = name; this.age = age; this.toString = function() { return this.name + " is " + age + " years old."; }; } var john = new Person("John Galt", 50); console.log(john.toString()); Note that by convention the name of a constructor function is always written in Pascal Case (the first letter of each word is capital). This is to distinguish between constructor functions and other functions. It is important that constructor functions be called with the ‘new’ keyword and that not constructor functions are not. There are two problems with the pattern constructor function pattern shown above: It makes inheritance difficult The toString() function is redefined for each new object created by the Person constructor. This is sub-optimal because the function should be shared between all of the instances of the Person type. Constructor Functions with a Prototype JavaScript functions have a special property called prototype. When an object is created by calling a JavaScript constructor all of the properties of the constructor’s prototype become available to the new object. In this way many Person objects can be created that can access the same prototype. An improved version of the above example can be written: function Person(name, age) { this.name = name; this.age = age; } Person.prototype = { toString: function() { return this.name + " is " + this.age + " years old."; } }; var john = new Person("John Galt", 50); console.log(john.toString()); In this version a single instance of the toString() function will now be shared between all Person objects. Private Members The short version is: there aren’t any. If a variable is defined, with the var keyword, within the constructor function then its scope is that function. Other functions defined within the constructor function will be able to access the private variable, but anything defined outside the constructor (such as functions on the prototype property) won’t have access to the private variable. Any variables defined on the constructor are automatically public. Some people solve this problem by prefixing properties with an underscore and then not calling those properties by convention. function Person(name, age) { this.name = name; this.age = age; } Person.prototype = { _getName: function() { return this.name; }, toString: function() { return this._getName() + " is " + this.age + " years old."; } }; var john = new Person("John Galt", 50); console.log(john.toString()); Note that the _getName() function is only private by convention – it is in fact a public function. Functional Object Construction Because of the weirdness involved in using constructor functions some JavaScript developers prefer to eschew them completely. They theorize that it is better to work with JavaScript’s functional nature than to try and force it to behave like a traditional class-oriented language. When using the functional approach objects are created by returning them from a factory function. An excellent side effect of this pattern is that variables defined with the factory function are accessible to the new object (due to closure) but are inaccessible from anywhere else. The Person example implemented using the functional object construction pattern is: var personFactory = function(name, age) { var privateVar = 7; return { toString: function() { return name + " is " + age * privateVar / privateVar + " years old."; } }; }; var john2 = personFactory("John Lennon", 40); console.log(john2.toString()); Note that the ‘new’ keyword is not used for this pattern, and that the toString() function has access to the name, age and privateVar variables because of closure. This pattern can be extended to provide inheritance and, unlike the constructor function pattern, it supports private variables. However, when working with JavaScript code bases you will find that the constructor function is more common – probably because it is a better approximation of mainstream class oriented languages like C# and Java. Inheritance Both of the above patterns can support inheritance but for now, favour composition over inheritance. Summary When JavaScript code exceeds simple browser automation object orientation can provide a powerful paradigm for controlling complexity. Both of the patterns presented in this article work – the choice is a matter of style. Only one question still remains; who is John Galt?

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  • JavaScript Class Patterns

    - by Liam McLennan
    To write object-oriented programs we need objects, and likely lots of them. JavaScript makes it easy to create objects: var liam = { name: "Liam", age: Number.MAX_VALUE }; But JavaScript does not provide an easy way to create similar objects. Most object-oriented languages include the idea of a class, which is a template for creating objects of the same type. From one class many similar objects can be instantiated. Many patterns have been proposed to address the absence of a class concept in JavaScript. This post will compare and contrast the most significant of them. Simple Constructor Functions Classes may be missing but JavaScript does support special constructor functions. By prefixing a call to a constructor function with the ‘new’ keyword we can tell the JavaScript runtime that we want the function to behave like a constructor and instantiate a new object containing the members defined by that function. Within a constructor function the ‘this’ keyword references the new object being created -  so a basic constructor function might be: function Person(name, age) { this.name = name; this.age = age; this.toString = function() { return this.name + " is " + age + " years old."; }; } var john = new Person("John Galt", 50); console.log(john.toString()); Note that by convention the name of a constructor function is always written in Pascal Case (the first letter of each word is capital). This is to distinguish between constructor functions and other functions. It is important that constructor functions be called with the ‘new’ keyword and that not constructor functions are not. There are two problems with the pattern constructor function pattern shown above: It makes inheritance difficult The toString() function is redefined for each new object created by the Person constructor. This is sub-optimal because the function should be shared between all of the instances of the Person type. Constructor Functions with a Prototype JavaScript functions have a special property called prototype. When an object is created by calling a JavaScript constructor all of the properties of the constructor’s prototype become available to the new object. In this way many Person objects can be created that can access the same prototype. An improved version of the above example can be written: function Person(name, age) { this.name = name; this.age = age; } Person.prototype = { toString: function() { return this.name + " is " + this.age + " years old."; } }; var john = new Person("John Galt", 50); console.log(john.toString()); In this version a single instance of the toString() function will now be shared between all Person objects. Private Members The short version is: there aren’t any. If a variable is defined, with the var keyword, within the constructor function then its scope is that function. Other functions defined within the constructor function will be able to access the private variable, but anything defined outside the constructor (such as functions on the prototype property) won’t have access to the private variable. Any variables defined on the constructor are automatically public. Some people solve this problem by prefixing properties with an underscore and then not calling those properties by convention. function Person(name, age) { this.name = name; this.age = age; } Person.prototype = { _getName: function() { return this.name; }, toString: function() { return this._getName() + " is " + this.age + " years old."; } }; var john = new Person("John Galt", 50); console.log(john.toString()); Note that the _getName() function is only private by convention – it is in fact a public function. Functional Object Construction Because of the weirdness involved in using constructor functions some JavaScript developers prefer to eschew them completely. They theorize that it is better to work with JavaScript’s functional nature than to try and force it to behave like a traditional class-oriented language. When using the functional approach objects are created by returning them from a factory function. An excellent side effect of this pattern is that variables defined with the factory function are accessible to the new object (due to closure) but are inaccessible from anywhere else. The Person example implemented using the functional object construction pattern is: var john = new Person("John Galt", 50); console.log(john.toString()); var personFactory = function(name, age) { var privateVar = 7; return { toString: function() { return name + " is " + age * privateVar / privateVar + " years old."; } }; }; var john2 = personFactory("John Lennon", 40); console.log(john2.toString()); Note that the ‘new’ keyword is not used for this pattern, and that the toString() function has access to the name, age and privateVar variables because of closure. This pattern can be extended to provide inheritance and, unlike the constructor function pattern, it supports private variables. However, when working with JavaScript code bases you will find that the constructor function is more common – probably because it is a better approximation of mainstream class oriented languages like C# and Java. Inheritance Both of the above patterns can support inheritance but for now, favour composition over inheritance. Summary When JavaScript code exceeds simple browser automation object orientation can provide a powerful paradigm for controlling complexity. Both of the patterns presented in this article work – the choice is a matter of style. Only one question still remains; who is John Galt?

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  • Which book should I pick to improve my program designs/design patterns?

    - by zxcvbnm
    I want to learn about design patterns and from what I've seen the most recommended ones are the Gang of Four's Design Patterns and Head First Design Patterns. There are also language specific books, but I never see them recommended. I suppose it ties you to whatever strengths/weaknesses are inherent to each language, so not a good idea to learn design patterns in general. The Gang of Four's book is kinda old, so I'm wondering if there isn't a better alternative out today? I've heard the Heard First one isn't quite as good. But I'm not sure why, so it's really hard to pick either one. I've see some answers on this very site recommending both, but if I can only read one, which should I pick? I've been coding for 3+ years, though I've never had a good class on this subject. Also, would a book like Code Complete help me with this? One more thing: how often are these techniques supposed to be useful? For example, this question has me wondering if this stuff is worth the trouble. And please, tell me more than just "read x". I'd like to know why you're suggesting x.

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