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  • Alternative to "inheritance v composition??"

    - by Frank
    I have colleagues at work who claim that "Inheritance is an anti-pattern" and want to use composition systematically instead, except in (rare, according to them) cases where inheritance is really the best way to go. I want to suggest an alternative where we continue using inheritance, but it is strictly forbidden (enforced by code reviews) to use anything but public members of base classes in derived classes. For a case where we don't need to swap components of a class at runtime (static inheritance), would that be equivalent enough to composition? Or am I forgetting some other important aspect of composition?

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  • Advice on developing a social network [on hold]

    - by Siraj Mansour
    I am doing research on assembling a team, using the right tools, and the cost to develop a highly responsive social network that is capable of dealing with a lot of users. Similar to the Facebook concept but using the basics package for now. Profile, friends, posts, updates, media upload/download, streaming, chat and Inbox messaging are all in the package. We certainly do not expect it to be as popular as Facebook or handle the same number of users and requests, but in its own game it has to be a monster, and expandable for later on. Neglecting the hosting, and servers part, i am looking for technical advise and opinions, on what kind of team i need ? how many developers ? their expertise ? What are the right tools ? languages ? frameworks ? environments ? Any random ideas about the infrastructure ? Quick thoughts on the development process ? Please use references, if you have any to support your ideas. Development cost mere estimation ? NEGLECTING THE COST OF SERVERS I know my question is too broad but my knowledge is very limited and i need detailed help, for any help you can offer i thank you in advance.

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  • Data Transformation Pipeline

    - by davenewza
    I have create some kind of data pipeline to transform coordinate data into more useful information. Here is the shell of pipeline: public class PositionPipeline { protected List<IPipelineComponent> components; public PositionPipeline() { components = new List<IPipelineComponent>(); } public PositionPipelineEntity Process(Position position) { foreach (var component in components) { position = component.Execute(position); } return position; } public PositionPipeline RegisterComponent(IPipelineComponent component) { components.Add(component); return this; } } Every IPipelineComponent accepts and returns the same type - a PositionPipelineEntity. Code: public interface IPipelineComponent { PositionPipelineEntity Execute(PositionPipelineEntity position); } The PositionPipelineEntity needs to have many properties, many which are unused in certain components and required in others. Some properties will also have become redundant at the end of the pipeline. For example, these components could be executed: TransformCoordinatesComponent: Parse the raw coordinate data into a Coordinate type. DetermineCountryComponent: Determine and stores country code. DetermineOnRoadComponent: Determine and store whether coordinate is on a road. Code: pipeline .RegisterComponent(new TransformCoordinatesComponent()) .RegisterComponent(new DetermineCountryComponent()) .RegisterComponent(new DetermineOnRoadComponent()); pipeline.Process(positionPipelineEntity); The PositionPipelineEntity type: public class PositionPipelineEntity { // Only relevant to the TransformCoordinatesComponent public decimal RawCoordinateLatitude { get; set; } // Only relevant to the TransformCoordinatesComponent public decimal RawCoordinateLongitude { get; set; } // Required by all components after TransformCoordinatesComponent public Coordinate CoordinateLatitude { get; set; } // Required by all components after TransformCoordinatesComponent public Coordinate CoordinateLongitude { get; set; } // Set in DetermineCountryComponent, not required anywhere. // Requires CoordinateLatitude and CoordinateLongitude (TransformCoordinatesComponent) public string CountryCode { get; set; } // Set in DetermineOnRoadComponent, not required anywhere. // Requires CoordinateLatitude and CoordinateLongitude (TransformCoordinatesComponent) public bool OnRoad { get; set; } } Problems: I'm very concerned about the dependency that a component has on properties. The way to solve this would be to create specific types for each component. The problem then is that I cannot chain them together like this. The other problem is the order of components in the pipeline matters. There is some dependency. The current structure does not provide any static or runtime checking for such a thing. Any feedback would be appreciated.

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  • Need to re-build an application - how?

    - by Tom
    For our main system, we have a small monitor application that sits outside our network and periodically tries to log in to verify the system still works. We have a problem with the monitor though in that the communications component set (Asta 3 inside Delphi applications) doesn't always connect through. Overall, I'd say it's about 95% reliable, but that other 5% kills the monitor since it will try to log in and hang on the connection attempt (no timeout in the component). This really isn't an issue on the client side of the system since the clients don't disconnect and reconnect repeatedly on the same application instance, but I need a way to make sure the monitor stays up and continues working even when the component fails on a run. I have a few ideas as to which way to have the program run, the main idea being to put the communications inside a threaded data module so that if one thread crashes then another thread can test later and the program keep going. Does this sound like a valid way to go? Any other ideas how to ensure a reliable monitoring application with a less than 100% reliable component? Thanks. P.S. Not sure these tags are the most appropriate. Tried including "system-reliability" as one, but not high enough rep to create.

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  • Defining formula through user interface in user form

    - by BriskLabs Pakistan
    I am a student and developing a simple assignment - windows form application in visual studio 2010. The application is suppose to construct formulas as per user requirement. The process: It has to pick data from columns of Microsoft Access database and the user should be able to pick the data by column name like we do in a drop down menu. and create reusable formulas in it ( configure it once and can change it again). followings are column titles from database that can be picked for example. e.g Col -1 : Marks in Maths Col -2 : Total Marks in Maths Col -3 : Marks in science Col -4 : Total marks in science Finally we should be able to construct any formula in the UI like (Col 1 + Col 3 ) / ( col 2 + col 4) = Formula 1 once this is formula is set saved and a name is assigned to it by user. he/she can use the formula and results shall appear in a window below. i.e He would be able to calculate his desired figures (formula) by only manipulating underlying data on the UI layer....choose the data for a period and apply the formula and get the answer Problem: It looks like I have to create an app where rules are set through UI....... this means no stored procedures are required in SQL.... please suggest the right approach.

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  • Is it better to define all routes in the Global.asax than to define separately in the areas?

    - by Matthew Patrick Cashatt
    I am working on a MVC 4 project that will serve as an API layer of a larger application. The developers that came before me set up separate Areas to separate different API requests (i.e Search, Customers, Products, and so forth). I am noticing that each Area has separate Area registration classes that define routes for that area. However, the routes defined are not area-specific (i.e. {controller}/{action}/{id} might be defined redundantly in a couple of areas). My instinct would be to move all of these route definitions to a common place like the Global.asax to avoid redundancy and collisions, but I am not sure if I am correct about that.

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  • Is an event loop just a for/while loop with optimized polling?

    - by Alan
    I'm trying to understand what an event loop is. Often the explanation is that in the event loop, you do something until you're notified that an event occurred. You than handle the event and continue doing what you did before. To map the above definition with an example. I have a server which 'listens' in a event loop, and when a socket connection is detected, the data from it gets read and displayed, after which the server goes to the listening it did before. However, this event happening and us getting notified 'just like that' are to much for me to handle. You can say: "It's not 'just like that' you have to register an event listener". But what's an event listener but a function which for some reason isn't returning. Is it in it's own loop, waiting to be notified when an event happens? Should the event listener also register an event listener? Where does it end? Events are a nice abstraction to work with, however just an abstraction. I believe that in the end, polling is unavoidable. Perhaps we are not doing it in our code, but the lower levels (the programming language implementation or the OS) are doing it for us. It basically comes down to the following pseudo code which is running somewhere low enough so it doesn't result in busy waiting: while(True): do stuff check if event has happened (poll) do other stuff This is my understanding of the whole idea, and i would like to hear if this is correct. I am open in accepting that the whole idea is fundamentally wrong, in which case I would like the correct explanation. Best regards

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  • How to prevent duplicate data access methods that retrieve similar data?

    - by Ronald Wildenberg
    In almost every project I work on with a team, the same problem seems to creep in. Someone writes UI code that needs data and writes a data access method: AssetDto GetAssetById(int assetId) A week later someone else is working on another part of the application and also needs an AssetDto but now including 'approvers' and writes the following: AssetDto GetAssetWithApproversById(int assetId) A month later someone needs an asset but now including the 'questions' (or the 'owners' or the 'running requests', etc): AssetDto GetAssetWithQuestionsById(int assetId) AssetDto GetAssetWithOwnersById(int assetId) AssetDto GetAssetWithRunningRequestsById(int assetId) And it gets even worse when methods like GetAssetWithOwnerAndQuestionsById start to appear. You see the pattern that emerges: an object is attached to a large object graph and you need different parts of this graph in different locations. Of course, I'd like to prevent having a large number of methods that do almost the same. Is it simply a matter of team discipline or is there some pattern I can use to prevent this? In some cases it might make sense to have separate methods, i.e. getting an asset with running requests may be expensive so I do not want to include these all the time. How to handle such cases?

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  • Liskov substitution principle with abstract parent class

    - by Songo
    Does Liskov substitution principle apply to inheritance hierarchies where the parent is an abstract class the same way if the parent is a concrete class? The Wikipedia page list several conditions that have to be met before a hierarchy is deemed to be correct. However, I have read in a blog post that one way to make things easier to conform to LSP is to use abstract parent instead of a concrete class. How does the choice of the parent type (abstract vs concrete) impacts the LSP? Is it better to have an abstract base class whenever possible?

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  • What should a domain object's validation cover?

    - by MarcoR88
    I'm trying to figure out how to do validation of domain objects that need external resources, such as data mappers/dao Firstly here's my code class User { const INVALID_ID = 1; const INVALID_NAME = 2; const INVALID_EMAIL = 4; int getID(); void setID(Int i); string getName(); void setName(String s); string getEmail(); void setEmail(String s); int getErrorsForInsert(); // returns a bitmask for INVALID_* constants int getErrorsForUpdate(); } My worries are about the uniqueness of the email, checking it would require the storage layer. Reading others' code seems that two solutions are equally accepted: both perform the unique validation in data mapper but some set an error state to the DO user.addError(User.INVALID_EMAIL) while others prefer to throw a totally different type of exception that covers only persistence, like: UserStorageException { const INVALID_EMAIL = 1; const INVALID_CITY = 2; } What are the pros and cons of these solutions?

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  • Looking for games in environments similar to a pinball table

    - by chaosTechnician
    I'm on a team of students working on a third-person adventure game that takes place inside a pinball machine (like, small scale, on the surface, avoiding pinballs, etc). One of my responsibilities on the project is to find games that are similar to this concept in appearance and/or gameplay for reference. So, does anyone know of games (other than pinball) that takes place in a pinball-like environment? Or, adventure games that take place in small, cramped environments with multiple paths around the world? Or games in which the player is often bombarded with balls (or other similar unintelligent obstacles)? Or games that take place on a small scale?

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  • Alternative to "inheritance versus composition?" [closed]

    - by Frank
    Possible Duplicate: Where does this concept of “favor composition over inheritance” come from? I have colleagues at work who claim that "Inheritance is an anti-pattern" and want to use composition systematically instead, except in (rare, according to them) cases where inheritance is really the best way to go. I want to suggest an alternative where we continue using inheritance, but it is strictly forbidden (enforced by code reviews) to use anything but public members of base classes in derived classes. For a case where we don't need to swap components of a class at runtime (static inheritance), would that be equivalent enough to composition? Or am I forgetting some other important aspect of composition?

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  • What is the best approach to solve a factory method problem which has to be an instance?

    - by Iago
    I have to add new funcionality in a web service legacy project and I'm thinking what is the best approach for a concrete situation. The web service is simple: It receives a XML file, unmarshalling, generates response's objects, marshalling and finally it sends the response as a XML file. For every XML files received, the web service always responds with the same XML structure. What I have to do is to generate a different XML file according to the XML received. So I have a controller class which has all marshalling/unmarshalling operations, but this controller class has to be an instance. Depending on XML received I need some marshalling methods or others. Trying to make few changes on legacy source, what is the best approach? My first approach was to do a factory method pattern with the controller class, but this class has to be an instance. I want to keep, as far as it goes, this structure: classController.doMarshalling(); I think this one is a bit smelly: if(XMLReceived.isTypeOne()) classController.doMarshallingOne(); else if(XMLReceived.isTypeTwo()) classController.doMarshallingTwo(); else if(XMLReceived.isTypeThree()) classController.doMarshallingThree(); else if ... I hope my question is well understood

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  • Enemy Spawning method in a Top-Down Shooter

    - by Chris Waters
    I'm working on a top-down shooter akin to DoDonPachi, Ikaruga, etc. The camera movement through the world is handled automatically with the player able to move inside of the camera's visible region. Along the way, enemies are scripted to spawn at particular points along the path. While this sounds straightforward, I could see two ways to define these points: Camera's position: 'trigger' spawning as the camera passes by the points Time along path: "30 seconds in, spawn 2 enemies" In both cases, the camera-relative positions would be defined as well as the behavior of the enemy. The way I see it, the way you define these points will directly affect how the 'level editor', or what have you, will work. Would there be any benefits of one approach over the other?

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  • When designing a job queue, what should determine the scope of a job?

    - by Stuart Pegg
    We've got a job queue system that'll cheerfully process any kind of job given to it. We intend to use it to process jobs that each contain 2 tasks: Job (Pass information from one server to another) Fetch task (get the data, slowly) Send task (send the data, comparatively quickly) The difficulty we're having is that we don't know whether to break the tasks into separate jobs, or process the job in one go. Are there any best practices or useful references on this subject? Is there some obvious benefit to a method that we're missing? So far we can see these benefits for each method: Split Job lease length reflects job length: Rather than total of two Finer granularity on recovery: If we lose outgoing connectivity we can tell them all to retry The starting state of the second task is saved to job history: Helps with debugging (although similar logging could be added in single task method) Single Single job to be scheduled: Less processing overhead Data not stale on recovery: If the outgoing downtime is quite long, the pending Send jobs could be outdated

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  • Best approach for saving highlighted areas on geographical map.

    - by Mohsen
    I am designing an application that allow users to highlight areas of a geographical map using a tool that is like brush or a pen. The tool basically draw a circle with a single click and continue drawing those circles with move move. Here is an example of drawing made by moving the tool. It is pretty much same as Microsoft Paint. Regardless of programming language what is best approach (most inexpensive approach) for saving this kind of data?

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  • DDD / Layers and legacy systems

    - by CSM
    I have to refactor a complex C# app (many dialogs, mixed logic and so on). There is a part managing the communication with special hardware equipments (sending commands and receive data via asynchronous c# callbacks). The code is "spaghetti" with mixed UI/Logic/Communication/etc and my task is to split the layers in a DDD sense. So, to which layer belongs a callback driver routine? The callbacks are creating "bubbles" in the system, up to the UI layer and because of this I cannot enforce the essential principle that any element of a layer depends only on other elements in the same layer or on elements of the layers "beneath" it. Thank you in advance.

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  • Best Method of function parameter validation

    - by Aglystas
    I've been dabbling with the idea of creating my own CMS for the experience and because it would be fun to run my website off my own code base. One of the decisions I keep coming back to is how best to validate incoming parameters for functions. This is mostly in reference to simple data types since object validation would be quite a bit more complex. At first I debated creating a naming convention that would contain information about what the parameters should be, (int, string, bool, etc) then I also figured I could create options to validate against. But then in every function I still need to run some sort of parameter validation that parses the parameter name to determine what the value can be then validate against it, granted this would be handled by passing the list of parameters to function but that still needs to happen and one of my goals is to remove the parameter validation from the function itself so that you can only have the actual function code that accomplishes the intended task without the additional code for validation. Is there any good way of handling this, or is it so low level that typically parameter validation is just done at the start of the function call anyway, so I should stick with doing that.

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  • Applying DDD principles in a RESTish web service

    - by Andy
    I am developing an RESTish web service. I think I got the idea of the difference between aggregation and composition. Aggregation does not enforce lifecycle/scope on the objects it references. Composition does enforce lifecycle/scope on the objects it contain/own. If I delete a composite object then all the objects it contain/own are deleted as well, while the deleting an aggregate root does not delete referenced objects. 1) If it is true that deleting aggregate roots does not necessary delete referenced objects, what sense does it make to not have a repository for the references objects? Or are aggregate roots as a term referring to what is known as composite object? 2) When you create an web service you will have multiple endpoints, in my case I have one entity Book and another named Comment. It does not make sense to leave the comments in my application if the book is deleted. Therefore, book is a composite object. I guess I should not have a repository for comments since that would break the enforcement of lifecycle and rules that the book class may have. However I have URL such as (examples only): GET /books/1/comments POST /books/1/comments Now, if I do not have a repository for comments, does that mean I have to load the book object and then return the referenced comments? Am I allowed to return a list of Comment entities from the BookRepository, does that make sense? The repository for Book may eventually become rather big with all sorts of methods. Am I allowed to write JPQL (JPA queries) that targets comments and not books inside the repository? What about pagination and filtering of comments. When adding a new comment triggered by the POST endpoint, do you need to load the book, add the comment to the book, and then update the whole book object? What I am currently doing is having a own CommentRepository, even though the comments are deleted with the book. I could need some direction on how to do it correct. Since you are exposing not only root objects in RESTish services I wonder how to handle this at the backend. I am using Hibernate and Spring.

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  • Callbacks: when to return value, and when to modify parameter?

    - by MarkN
    When writing a callback, when is best to have the callback return a value, and when is it best to have the callback modify a parameter? Is there a difference? For example, if we wanted to grab a list of dependencies, when would you do this: function GetDependencies(){ return [{"Dep1" : 1.1}, {"Dept2": 1.2}, {"Dep3" : 1.3}]; } And when would you do this? function RegisterDependencies(register){ register.add("Dep1", 1.1); register.add("Dep2", 1.2); register.add("Dep3", 1.3); }

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  • Is OOP becoming easier or harder?

    - by tunmise fasipe
    When the concepts of Object Oriented Programming were introduced to programmers years back it looks interesting and programming was cleaner. OOP was like this Stock stock = new Stock(); stock.addItem(item); stock.removeItem(item); That was easier to understand with self-descriptive name. But now OOP, with pattern like Data Transfer Objects (or Value Objects), Repository, Dependency Injection etc, has become more complex. To achieve the above you may have to create several classes (e.g. abstract, factory, DAO etc) and Implement several interfaces Note: I am not against best practices that makes Collaboration, Testing and Integration easier

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  • Creating Objects

    - by user1424667
    I have a general coding standard question. Is it bad practice to initialize and create an object in multiple methods depending on the outcome of a users choice. So for example if the user quits a poker game, create the poker hand with the cards the user has received, even if < 5, and if the user played till the end create object to show completed hand to show outcome of the game. The key is that the object will only be created once in actuality, there are just different paths and parameters is will receive depending on if the user folded, or played on to the showdown.

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  • Is it wrong to use a boolean parameter to determine behavior?

    - by Ray
    I have seen a practice from time to time that "feels" wrong, but I can't quite articulate what is wrong about it. Or maybe it's just my prejudice. Here goes: A developer defines a method with a boolean as one of its parameters, and that method calls another, and so on, and eventually that boolean is used, solely to determine whether or not to take a certain action. This might be used, for example, to allow the action only if the user has certain rights, or perhaps if we are (or aren't) in test mode or batch mode or live mode, or perhaps only when the system is in a certain state. Well there is always another way to do it, whether by querying when it is time to take the action (rather than passing the parameter), or by having multiple versions of the method, or multiple implementations of the class, etc. My question isn't so much how to improve this, but rather whether or not it really is wrong (as I suspect), and if it is, what is wrong about it.

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  • Seperation of drawing and logic in games

    - by BFree
    I'm a developer that's just now starting to mess around with game development. I'm a .Net guy, so I've messed with XNA and am now playing around with Cocos2d for the iPhone. My question really is more general though. Let's say I'm building a simple Pong game. I'd have a Ball class and a Paddle class. Coming from the business world development, my first instinct is to not have any drawing or input handling code in either of these classes. //pseudo code class Ball { Vector2D position; Vector2D velocity; Color color; void Move(){} } Nothing in the ball class handles input, or deals with drawing. I'd then have another class, my Game class, or my Scene.m (in Cocos2D) which would new up the Ball, and during the game loop, it would manipulate the ball as needed. The thing is though, in many tutorials for both XNA and Cocos2D, I see a pattern like this: //pseudo code class Ball : SomeUpdatableComponent { Vector2D position; Vector2D velocity; Color color; void Update(){} void Draw(){} void HandleInput(){} } My question is, is this right? Is this the pattern that people use in game development? It somehow goes against everything I'm used to, to have my Ball class do everything. Furthermore, in this second example, where my Ball knows how to move around, how would I handle collision detection with the Paddle? Would the Ball need to have knowledge of the Paddle? In my first example, the Game class would have references to both the Ball and the Paddle, and then ship both of those off to some CollisionDetection manager or something, but how do I deal with the complexity of various components, if each individual component does everything themselves? (I hope I'm making sense.....)

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  • How to implement Restricted access to application features

    - by DroidUser
    I'm currently developing a web application, that provides some 'service' to the user. The user will have to select a 'plan' according to which she/he will be allowed to perform application specific actions but up to a limit defined by the plan. A Plan will also limit access to certain features, which will not be available at all for some plans. As an example : say there are 3 plans, 2 actions throughout the application users in plan-1 can perform action-1 3 times, and they can't perform action-2 at all users in plan-2 can perform action-1 10 times, action-2 5 times users in plan-3 can perform action-1 20 times, action-2 10 times So i'm looking for the best way to get this done, and my main concerns besides implementing it, are the following(in no particular order) maintainability/changeability : the number of plans, and type of features/actions will change in the final product industry standard/best practice : for future readiness!! efficiency : ofcourse, i want fast code!! I have never done anything like this before, so i have no clue about how do i go about implementing these functionalities. Any tips/guides/patterns/resources/examples? I did read a little about ACL, RBAC, are they the patterns that i need to follow? Really any sort of feedback will help.

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