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• Clean MVC design when there is viewer latency

  - by Tony Suffolk 66

  It isn't clear if this question has already been answered, so apologies in advance if this is a duplicate : I am implementing a game and trying to design around a clean MVC pattern - so my Control plane will implement the rules of the game (but not how the game is displayed), and the View plane implements how the game is displayed, and user iteraction - i.e. what game items or controls the user has activated. The challenge that I have is this : In my game the Control Plane can move game items more or less instaneously (The decision about what item to place where - and some of the initial consequences of that placement are reasonably trivial to calculate), but I want to design the Control Plane so that the View plane can display these movements either instaneously or using movement animations. The other complication is that player interaction must be locked out while those game items are moving (similar to chess - you can't attack an opposing piece as it moves past one of your pieces) So do I : Implement all the logic in the Control Plane asynchronously - and separate the descision making from the actions - so the Control plane decides piece 'A' needs to move to a given place - tells the view plane, and but does not implement the move in data until the view plane informs the control plane that the move/animation is complete. A lot of interlock points between the two layers. Implement all the control plane logic in one place - decisions and movement (keeping track of what moved where), and pass all the movements in one go to the View plane to do with what it will. Control Plane is almost fire and forget here. A hybrid of 1 & 2 - The control plane implements all the moves in a temporary data store - but maintains a second store which reflects what is actually visible to the viewer, based on calls and feedback from the View plane. All 3 are relatively easy to implement (target language is python), but having never done a clean MVC pattern with view latency before - I am not sure which design is best

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• Techniques for separating game model from presentation

  - by liortal

  I am creating a simple 2D game using XNA. The elements that make up the game world are what i refer to as the "model". For instance, in a board game, i would have a GameBoard class that stores information about the board. This information could be things such as: Location Size Details about cells on the board (occupied/not occupied) etc This object should either know how to draw itself, or describe how to draw itself to some other entity (renderer) in order to be displayed. I believe that since the board only contains the data+logic for things regarding it or cells on it, it should not provide the logic of how to draw things (separation of concerns). How can i achieve a good partitioning and easily allow some other entity to draw it properly? My motivations for doing so are: Allow multiple "implementations" of presentation for a single game entity Easier porting to other environments where the presentation code is not available (for example - porting my code to Unity or other game technology that does not rely on XNA).

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• A sample Memento pattern: Is it correct?

  - by TheSilverBullet

  Following this query on memento pattern, I have tried to put my understanding to test. Memento pattern stands for three things: Saving state of the "memento" object for its successful retrieval Saving carefully each valid "state" of the memento Encapsulating the saved states from the change inducer so that each state remains unaltered Have I achieved these three with my design? Problem This is a zero player game where the program is initialized with a particular set up of chess pawns - the knight and queen. Then program then needs to keep adding set of pawns or knights and queens so that each pawn is "safe" for the next one move of every other pawn. The condition is that either both pawns should be placed, or none of them should be placed. The chessboard with the most number of non conflicting knights and queens should be returned. Implementation I have 4 classes for this: protected ChessBoard (the Memento) private int [][] ChessBoard; public void ChessBoard(); protected void SetChessBoard(); protected void GetChessBoard(int); public Pawn This is not related to memento. It holds info about the pawns public enum PawnType: int { Empty = 0, Queen = 1, Knight = 2, } //This returns a value that shown if the pawn can be placed safely public bool IsSafeToAddPawn(PawnType); public CareTaker This corresponds to caretaker of memento This is a double dimentional integer array that keeps a track of all states. The reason for having 2D array is to keep track of how many states are stored and which state is currently active. An example: 0 -2 1 -1 2 0 - This is current state. With second index 0/ 3 1 - This state has been saved, but has been undone private int [][]State; private ChessBoard [] MChessBoard; //This gets the chessboard at the position requested and assigns it to originator public ChessBoard GetChessBoard(int); //This overwrites the chessboard at given position public void SetChessBoard(ChessBoard, int); private int [][]State; public PlayGame (This is the originator) private bool status; private ChessBoard oChessBoard; //This sets the state of chessboard at position specified public SetChessBoard(ChessBoard, int); //This gets the state of chessboard at position specified public ChessBoard GetChessBoard(int); //This function tries to place both the pawns and returns the status of this attempt public bool PlacePawns(Pawn);

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• Representing complex object dependencies

  - by max

  I have several classes with a reasonably complex (but acyclic) dependency graph. All the dependencies are of the form: class X instance contains an attribute of class Y. All such attributes are set during initialization and never changed again. Each class' constructor has just a couple parameters, and each object knows the proper parameters to pass to the constructors of the objects it contains. class Outer is at the top of the dependency hierarchy, i.e., no class depends on it. Currently, the UI layer only creates an Outer instance; the parameters for Outer constructor are derived from the user input. Of course, Outer in the process of initialization, creates the objects it needs, which in turn create the objects they need, and so on. The new development is that the a user who knows the dependency graph may want to reach deep into it, and set the values of some of the arguments passed to constructors of the inner classes (essentially overriding the values used currently). How should I change the design to support this? I could keep the current approach where all the inner classes are created by the classes that need them. In this case, the information about "user overrides" would need to be passed to Outer class' constructor in some complex user_overrides structure. Perhaps user_overrides could be the full logical representation of the dependency graph, with the overrides attached to the appropriate edges. Outer class would pass user_overrides to every object it creates, and they would do the same. Each object, before initializing lower level objects, will find its location in that graph and check if the user requested an override to any of the constructor arguments. Alternatively, I could rewrite all the objects' constructors to take as parameters the full objects they require. Thus, the creation of all the inner objects would be moved outside the whole hierarchy, into a new controller layer that lies between Outer and UI layer. The controller layer would essentially traverse the dependency graph from the bottom, creating all the objects as it goes. The controller layer would have to ask the higher-level objects for parameter values for the lower-level objects whenever the relevant parameter isn't provided by the user. Neither approach looks terribly simple. Is there any other approach? Has this problem come up enough in the past to have a pattern that I can read about? I'm using Python, but I don't think it matters much at the design level.

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• Philosophy behind the memento pattern

  - by TheSilverBullet

  I have been reading up on memento pattern from various sources of the internet. Differing information from different sources has left me in confusion regarding why this pattern is actually needed. The dofactory implementation says that the primary intention of this pattern is to restore the state of the system. Wiki says that the primary intention is to be able to restore the changes on the system. This gives a different impact - saying that it is possible for a system to have memento implementation with no need to restore. And that ability of restore is a feature of this. OODesign says that It is sometimes necessary to capture the internal state of an object at some point and have the ability to restore the object to that state later in time. Such a case is useful in case of error or failure. So, my question is why exactly do we use this one? Is it to save previous states - or to promote encapsulation between the Caretaker and the Memento? Why is this type of encapsulation so important? Edit: For those visiting, check out this Implementation!

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• Caching factory design

  - by max

  I have a factory class XFactory that creates objects of class X. Instances of X are very large, so the main purpose of the factory is to cache them, as transparently to the client code as possible. Objects of class X are immutable, so the following code seems reasonable: # module xfactory.py import x class XFactory: _registry = {} def get_x(self, arg1, arg2, use_cache = True): if use_cache: hash_id = hash((arg1, arg2)) if hash_id in _registry: return _registry[hash_id] obj = x.X(arg1, arg2) _registry[hash_id] = obj return obj # module x.py class X: # ... Is it a good pattern? (I know it's not the actual Factory Pattern.) Is there anything I should change? Now, I find that sometimes I want to cache X objects to disk. I'll use pickle for that purpose, and store as values in the _registry the filenames of the pickled objects instead of references to the objects. Of course, _registry itself would have to be stored persistently (perhaps in a pickle file of its own, in a text file, in a database, or simply by giving pickle files the filenames that contain hash_id). Except now the validity of the cached object depends not only on the parameters passed to get_x(), but also on the version of the code that created these objects. Strictly speaking, even a memory-cached object could become invalid if someone modifies x.py or any of its dependencies, and reloads it while the program is running. So far I ignored this danger since it seems unlikely for my application. But I certainly cannot ignore it when my objects are cached to persistent storage. What can I do? I suppose I could make the hash_id more robust by calculating hash of a tuple that contains arguments arg1 and arg2, as well as the filename and last modified date for x.py and every module and data file that it (recursively) depends on. To help delete cache files that won't ever be useful again, I'd add to the _registry the unhashed representation of the modified dates for each record. But even this solution isn't 100% safe since theoretically someone might load a module dynamically, and I wouldn't know about it from statically analyzing the source code. If I go all out and assume every file in the project is a dependency, the mechanism will still break if some module grabs data from an external website, etc.). In addition, the frequency of changes in x.py and its dependencies is quite high, leading to heavy cache invalidation. Thus, I figured I might as well give up some safety, and only invalidate the cache only when there is an obvious mismatch. This means that class X would have a class-level cache validation identifier that should be changed whenever the developer believes a change happened that should invalidate the cache. (With multiple developers, a separate invalidation identifier is required for each.) This identifier is hashed along with arg1 and arg2 and becomes part of the hash keys stored in _registry. Since developers may forget to update the validation identifier or not realize that they invalidated existing cache, it would seem better to add another validation mechanism: class X can have a method that returns all the known "traits" of X. For instance, if X is a table, I might add the names of all the columns. The hash calculation will include the traits as well. I can write this code, but I am afraid that I'm missing something important; and I'm also wondering if perhaps there's a framework or package that can do all of this stuff already. Ideally, I'd like to combine in-memory and disk-based caching.

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• Need advice for approach for a web-based app that loads excel worksheet but exposes only the charts

  - by John

  I'm looking for suggestions on the Visual Studio approach to take for a web application that is in the conceptual stage. My environment has a lot of tools: Windows Server 2008 R2 Standard 64bit Visual Studio 2010 Professional Edition Sharepoint 2010 Server Enterprise Edition SQL Server 2008 R2 Office 2010 Professional I know I will need this app to retrieve data from a database (or a web service - not sure exactly at this point). The data needs to be placed in an Excel workbook dynamically. The app will need to have a nice user interface (standard web controls - perhaps with some Javascript effects). The Excel ribbon and worksheet grid will need to be hidden. Some web control(s) will cause the Excel chart(s) to be rendered. I am thinking this sounds like Visual Studio Tools for Office (VSTO) so as to leverage .Net and hide Excel. Can you offer suggestions regarding: One ASP.Net Web App Project One Class Library Project for Excel or perhaps which one of the several different Excel 2010 project types (addin, template, document) Would Excel Services for Sharepoint be useful (or required) ? I am feeling a little overwhelmed with so many choices at this early stage of conceptualizing the app. Can you suggest some ideas for this sort of thing? Also, I am a bit more experienced with C# but I've read VB.Net is better for work with the Excel object model. What are general advises with regard to tool choice and overall approach tradeoffs?

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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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• Are there any concerns with using a static read-only unit of work so that it behaves like a cache?

  - by Rowan Freeman

  Related question: How do I cache data that rarely changes? I'm making an ASP.NET MVC4 application. On every request the security details about the user will need to be checked with the area/controller/action that they are accessing to see if they are allowed to view it. The security information is stored in the database. For example: User Permission UserPermission Action ActionPermission A "Permission" is a token that is applied to an MVC action to indicate that the token is required in order to access the action. Once a user is given the permission (via the UserPermission table) then they have the token and can therefore access the action. I've been looking in to how to cache this data (since it rarely changes) so that I'm only querying in-memory data and not hitting a database (which is a considerable performance hit at the moment). I've tried storing things in lists, using a caching provider but I either run in to problems or performance doesn't improve. One problem that I constantly run in to is that I'm using lazy loading and dynamic proxies with EntityFramework. This means that even if I ToList() everything and store them somewhere static, the relationships are never populated. For example, User.Permissions is an ICollection but it's always null. I don't want to Include() everything because I'm trying to keep things simple and generic (and easy to modify). One thing I know is that an EntityFramework DbContext is a unit of work that acts with 1st-level caching. That is, for the duration of the unit of work, everything that is accessed is cached in memory. I want to create a read-only DbContext that will exist indefinitely and will only be used to read about permission data. Upon testing this it worked perfectly; my page load times went from 200ms+ to 20ms. I can easily force the data to refresh at certain intervals or simply leave it to refresh when the application pool is recycled. Basically it will behave like a cache. Note that the rest of the application will interact with other contexts that exist per request as normal. Is there any disadvantage to this approach? Could I be doing something different?

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• What is the difference between all-static-methods and applying a singleton pattern?

  - by shahensha

  I am making a database to store information about the users of my website (I am using stuts2 and hence Java EE technology). For the database I'll be making a DBManager. Should I apply singleton pattern here or rather make all it's methods static? I will be using this DBManager for basic things like adding, deleting and updating User profiles. Along with it, I'll use for all other querying purposes, for instance to find out whether a username already exists and to get all users for administrative purposes and stuff like that. My questions What is the benefit of singleton pattern? Which thing is most apt here? All static methods or a singleton pattern? Please compare both of them. regards shahensha P.S. The database is bigger than this. Here I am talking only about the tables which I'll be using for storing User Information.

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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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• Is there a good design pattern for this messaging class?

  - by salonMonsters

  Is there a good design pattern for this? I want to create a messaging class. The class will be passed: the type of message (eg. signup, signup confirmation, password reminder etc) the client's id The class needs to then look up the client's messaging preferences in the db (whether they want communication by email, sms or both) Then depending on the client's preference it will format the message for the medium (short version for sms, long form for email) and send it through our mail or sms provider's API. Because the fact that we want to be able to change out email and sms providers if need be I wondered if the Command Pattern would be a good choice.

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• What is a good design pattern / lib for iOS 5 to synchronize with a web service?

  - by Junto

  We are developing an iOS application that needs to synchronize with a remote server using web services. The existing web services have an "operations" style rather than REST (implemented in WCF but exposing JSON HTTP endpoints). We are unsure of how to structure the web services to best fit with iOS and would love some advice. We are also interested in how to manage the synchronization process within iOS. Without going into detailed specifics, the application allows the user to estimate repair costs at a remote site. These costs are broken down by room and item. If the user has an internet connection this data can be sent back to the server. Multiple photographs can be taken of each item, but they will be held in a separate queue, which sends when the connection is optimal (ideally wifi). Our backend application controls the unique ids for each room and item. Thus, each time we send these costs to the server, the server echoes the central database ids back, thus, that they can be synchronized in the mobile app. I have simplified this a little, since the operations contract is actually much larger, but I just want to illustrate the basic requirements without complicating matters. Firstly, the web service architecture: We currently have two operations: GetCosts and UpdateCosts. My assumption is that if we used a strict REST architecture we would need to break our single web service operations into multiple smaller services. This would make the services much more chatty and we would also have to guarantee a delivery order from the app. For example, we need to make sure that containing rooms are added before the item. Although this seems much more RESTful, our perception is that these extra calls are expensive connections (security checks, database calls, etc). Does the type of web api (operation over service focus) determine chunky vs chatty? Since this is mobile (3G), are we better handling lots of smaller messages, or a few large ones? Secondly, the iOS side. What is the current advice on how to manage data synchronization within the iOS (5) app itself. We need multiple queues and we need to guarantee delivery order in each queue (and technically, ordering between queues). The server needs to control unique ids and other properties and echo them back to the application. The application then needs to update an internal database and when re-updating, make sure the correct ids are available in the update message (essentially multiple inserts and updates in one call). Our backend has a ton of business logic operating on these cost estimates. We don't want any of this in the app itself. Currently the iOS app sends the cost data, and then the server echoes that data back with populated ids (and other data). The existing cost data is deleted and the echoed response data is added to the client database on the device. This is causing us problems, because any photos might not have been sent, but the original entity tree has been removed and replaced. Obviously updating the costs tree rather than replacing it would remove this problem, but I'm not sure if there are any nice xcode libraries out there to do such things. I welcome any advice you might have.

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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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• What the best way to wire up Entity Framework database context (model) to ViewModel in MVVM WPF?

  - by hal9k2

  As in the question above: What the best way to wire up Entity Framework database model (context) to viewModel in MVVM (WPF)? I am learning MVVM pattern in WPF, alot of examples shows how to implement model to viewModel, but models in that examples are just simple classes, I want to use MVVM together with entity framework model (base first approach). Whats the best way to wire model to viewModel. Thanks for answers. //ctor of ViewModel public ViewModel() { db = new PackageShipmentDBEntities(); // Entity Framework generated class ListaZBazy = new ObservableCollection<Pack>(db.Packs.Where(w => w.IsSent == false)); } This is my usual ctor of ViewModel, think there is a better way, I was reading about repository pattern, not sure if I can adapt this to WPF MVVM

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• Parallel Class/Interface Hierarchy with the Facade Design Pattern?

  - by Mike G

  About a third of my code is wrapped inside a Facade class. Note that this isn't a "God" class, but actually represents a single thing (called a Line). Naturally, it delegates responsibilities to the subsystem behind it. What ends up happening is that two of the subsystem classes (Output and Timeline) have all of their methods duplicated in the Line class, which effectively makes Line both an Output and a Timeline. It seems to make sense to make Output and Timeline interfaces, so that the Line class can implement them both. At the same time, I'm worried about creating parallel class and interface structures. You see, there are different types of lines AudioLine, VideoLine, which all use the same type of Timeline, but different types of Output (AudioOutput and VideoOutput, respectively). So that would mean that I'd have to create an AudioOutputInterface and VideoOutputInterface as well. So not only would I have to have parallel class hierarchy, but there would be a parallel interface hierarchy as well. Is there any solution to this design flaw? Here's an image of the basic structure (minus the Timeline class, though know that each Line has-a Timeline): NOTE: I just realized that the word 'line' in Timeline might make is sound like is does a similar function as the Line class. They don't, just to clarify.

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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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• Building a template engine - starting point

  - by Anirudh

  We're building a Django-based project with a template component. This component will be separate from the project as such and can be Django/Python, Node, Java or whatever works. The template has to be rendered into HTML. The templates will contain references to objects with properties that are defined in the DB, say, a Bus. For eg, it could be something like [object type="vehicle" weight="heavy"] and it would have to pull a random object from the DB fulfilling the criteria : type="vehicle" weight="heavy" (bus/truck/jet) and then substitute that tag with an image, say, of a Bus. Also it would have to be able to handle some processing. Eg: What is [X type="integer" lte="10"] + [Y type="integer" lte="10"] [option X+Y correct_ans="true"] [option X-Y correct_ans="false"] [option X+y+1 correct_ans="false"] The engine would be expected to fill in a random integer value <= 10 for X and Y and show radioboxes for each of the options. Would also have to store the fact that the first option is the correct answer. Does it to make sense to write something from the scratch? Or is it better to use an existing templating system (like Django's own templating system) as a starting point? Any suggestions on how I can approach this?

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• Making Modular, Reusable and Loosely Coupled MVC Components

  - by Dusan

  I am building MVC3 application and need some general guidelines on how to manage complex client side interaction between my components. Here is my definition of one component in general way: Component which has it's own controller, model and view. All of the component's logic is placed inside these three parts and component is sort of "standalone", it contains it's own form, data needed for interaction, updates itself with Ajax and so on. Beside this internal logic and behavior of the component, it needs to be able to "Talk" to the outside world. By this I mean it should provide data and events (sort of) so when this component gets embedded in pages can notify other components which then can update based on the current state and data. I have an idea to use client ViewModel (in java-script) which would hookup all relevant components on page and control interaction between them. This would make components reusable, modular - independent of the context in which they are used. How would you do this, I am a bit stuck as I do not know if this is a good approach and there is a technical possibility to achieve this using java-script/jquery. The confusing part is about update via Ajax, how to ensure that component is properly linked to ViewModel when component is Ajax updated (or even worse removed or dynamically added). Also, how should this ViewModel be constructed and which technicalities to use here and in components to work as synergy??? On the web, I have found the various examples of the similar approach, but they are oversimplified (even for dummies) or over specific and do not provide valuable resource or general solution for this kind of implementation. If you have some serious examples it would be, also, very helpful. Note: My aim is to make interactions between many components on the same page simpler and more robust and elegant.

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• How bad is it to have two methods with the same name but different signatures in two classes?

  - by Super User

  I have a design problem related to a public interface, the names of methods, and the understanding of my API and code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class has one public method named collision, and the second has one private method called _collision. The two methods differs in argument type and number. As an example let's say that _collision checks if the object is colliding with another object with certain conditions l, r, t, b (collide on the left side, right side, etc) and returns true or false. The public collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think it's better to avoid overloading the design with different names for methods that do almost the same thing, but in distinct contexts and classes. Is this clear enough to the reader or I should change the method's name?

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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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• How to implment the database for event conditions and item bonuses for a browser based game

  - by Saifis

  I am currently creating a browser based game, and was wondering what was the standard approach in making diverse conditions and status bonuses database wise. Currently considering two cases. Event Conditions Needs min 1000 gold Needs min Lv 10 Needs certain item. Needs fulfillment of another event Status Bonus Reduces damage by 20% +100 attack points Deflects certain type of attack I wish to be able to continually change these parameters during the process of production and operation, so having them hard-coded isn't the best way. All I could come up with are the following two methods. Method 1 Create a table that contains each conditions with needed attributes Have a model named conditions with all the attributes it would need to set them conditions condition_type (level, money_min, money_max item, event_aquired) condition_amount prerequisite_condition_id prerequisite_item_id Method 2 write it in a DSL form that could be interpreted later in the code Perhaps something like yaml, have a text area in the setting form and have the code interpret it. condition_foo: condition_type :level min_level: 10 condition_type :item item_id: 2 At current Method 2 looks to be more practical and flexible for future changes, trade off being that all the flex must be done on the code side. Not to sure how this is supposed to be done, is it supposed to be hard coded? separate config file? Any help would be appreciated. Added For additional info, it will be implemented with Ruby on Rails

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• Do you leverage the benefits of the open-closed principle?

  - by Kaleb Pederson

  The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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• How essential is it to make a service layer?

  - by BornToCode

  I started building an app in 3 layers (DAL, BL, UI) [it mainly handles CRM, some sales reports and inventory]. A colleague told me that I must move to service layer pattern, that developers came to service pattern from their experience and it is the better approach to design most applications. He said it would be much easier to maintain the application in the future that way. Personally, I get the feeling that it's just making things more complex and I couldn't see much of a benefit from it that would justify that. This app does have an additional small partial ui that uses some (but only few) of the desktop application functions so I did find myself duplicating some code (but not much). Just because of some code duplication I wouldn't convert it to be service oriented, but he said I should use it anyway because in general it's a very good architecture, why programmers are so in love with services?? I tried to google on it but I'm still confused and can't decide what to do.

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• Single or multiple return statements in a function [on hold]

  - by Juan Carlos Coto

  When writing a function that can have several different return values, particularly when different branches of code return different values, what is the cleanest or sanest way of returning? Please note the following are really contrived examples meant only to illustrate different styles. Example 1: Single return def my_function(): if some_condition: return_value = 1 elif another_condition: return_value = 2 else: return_value = 3 return return_value Example 2: Multiple returns def my_function(): if some_condition: return 1 elif another_condition: return 2 else: return 3 The second example seems simpler and is perhaps more readable. The first one, however, might describe the overall logic a bit better (the conditions affect the assignment of the value, not whether it's returned or not). Is the second way preferable to the first? Why?

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