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• MVC pattern synchronisation

  - by Hariprasad

  I am facing a problem in synchronizing my model and view threads I have a view which is table. In it, user can select a few rows. I update the view as soon as the user clicks on any row since I don't want the UI to be slow. This updating is done by a logic which runs in the controller thread below. At the same time, the controller will update the model data too, which takes place in a different thread. i.e., controller puts the query in a queue, which is then executed by the model thread - which is a single-threaded interface. As soon as the query executes, controller will get a signal. Now, In order to keep the view and model synchronized, I will update the view again based on the return value of the query (the data returned by model) - even though I updated the view already for that user action. But, I am facing issues because, its taking a lot of time for the model to return the result, by that time user would have performed multiple clicks. So, as a result of updating the view again based on the information from model, the view sometimes goes back to the state in which the previous clicks were made (Suppose user clicks thrice on different rows. I update the view as soon as the click happens. Also, I update the view when I get data back from the model - which is supposed to be same as the already updated state of the view. Now, when the user clicks third time, I get data for the first click from model. As a result, view goes back to a state which is generated by the first click) Is there any way to handle such a synchronization issue?

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• How much game dev does $x amount of money get you?

  - by Frank

  How much a game costs to make gets asked often and is always answered with it depends or varies on the quality of the game. Well this is basically the same question but is a bit more precise. I'm wonder what quality of game you can make with varying degrees of funds. Lets say 500k, 1m, 2m, 5m, 10m, 15m, and 20m. Let's assume you don't do any of it yourself and it only covers development only... no advertising or manufacturing.

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• Isn't class scope purely for organization?

  - by Di-0xide

  Isn't scope just a way to organize classes, preventing outside code from accessing certain things you don't want accessed? More specifically, is there any functional gain to having public, protected, or private-scoped methods? Is there any advantage to classifying method/property scope rather than to, say, just public-ize everything? My presumption says no simply because, in binary code, there is no sense of scope (other than r/w/e, which isn't really scope at all, but rather global permissions for a block of memory). Is this correct? What about in languages like Java and C#[.NET]?

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• How should UI layer pass user input to BL layer?

  - by BornToCode

  I'm building an n-tier application, I have UI, BL, DAL & Entities (built from POCO) projects. (All projects have a reference to the Entities). My question is - how should I pass user input from the UI to the BL, as a bunch of strings passed to the BL method and the BL will build the object from the parameters, or should I build the objects inside the UI submit_function and send objects as parameters? EDIT: I wrote n-tier application, but what I actually meant was just layers.

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• find and replace app for ms word

  - by kittensatplay

  i program in python. i want to know if a program in python will work for ms word since ms word is not open source. the program basically changes words like ms word already does BUT it changes words based of off a list you write, which from what i know ms word doesnt do. if it does, just let me know. if there is a related program that is needed for a program in python or any language to work with a closed source software, jsut let me know.b also you can link to a phython specific place to ask phython related question if you know of one since im going to have a lot more in the future

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• How to name multi-setter?

  - by IAdapter

  I'm struggling with how to name this method, I don't like the "set" prefix, because I feel it should be reserved for normal "dumb" setters and some tools might not like it (i did not check it in checkstyle, pmd, etc., but I got a feeling they won't like it.) for example (in java, but I feel its language agnostic) public void setField1Field2(String field1, String field2) { this.field1 = field1; this.field2 = field2; } The only purpose of this method is ONLY to set, this method is needed and cannot be joined with any other (because of framework used).

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• Why is x=x++ undefined?

  - by ugoren

  It's undefined because the it modifies x twice between sequence points. The standard says it's undefined, therefore it's undefined. That much I know. But why? My understanding is that forbidding this allows compilers to optimize better. This could have made sense when C was invented, but now seems like a weak argument. If we were to reinvent C today, would we do it this way, or can it be done better? Or maybe there's a deeper problem, that makes it hard to define consistent rules for such expressions, so it's best to forbid them? So suppose we were to reinvent C today. I'd like to suggest simple rules for expressions such as x=x++, which seem to me to work better than the existing rules. I'd like to get your opinion on the suggested rules compared to the existing ones, or other suggestions. Suggested Rules: Between sequence points, order of evaluation is unspecified. Side effects take place immediately. There's no undefined behavior involved. Expressions evaluate to this value or that, but surely won't format your hard disk (strangely, I've never seen an implementation where x=x++ formats the hard disk). Example Expressions x=x++ - Well defined, doesn't change x. First, x is incremented (immediately when x++ is evaluated), then it's old value is stored in x. x++ + ++x - Increments x twice, evaluates to 2*x+2. Though either side may be evaluated first, the result is either x + (x+2) (left side first) or (x+1) + (x+1) (right side first). x = x + (x=3) - Unspecified, x set to either x+3 or 6. If the right side is evaluated first, it's x+3. It's also possible that x=3 is evaluated first, so it's 3+3. In either case, the x=3 assignment happens immediately when x=3 is evaluated, so the value stored is overwritten by the other assignment. x+=(x=3) - Well defined, sets x to 6. You could argue that this is just shorthand for the expression above. But I'd say that += must be executed after x=3, and not in two parts (read x, evaluate x=3, add and store new value). What's the Advantage? Some comments raised this good point. It's not that I'm after the pleasure of using x=x++ in my code. It's a strange and misleading expression. What I want is to be able to understand complicated expressions. Normally, a complicated expression is no more than the sum of its parts. If you understand the parts and the operators combining them, you can understand the whole. C's current behavior seems to deviate from this principle. One assignment plus another assignment suddenly doesn't make two assignments. Today, when I look at x=x++, I can't say what it does. With my suggested rules, I can, by simply examining its components and their relations.

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• Is executing SQL through a WebService a really bad idea?

  - by Kyle

  Typically when creating a simple tool or something that has to use a database, I go through the fairly long process of first creating a webservice that connects to a database then creating methods on this webservice that do all the type of queries I need.. methods like List<Users> GetUsers() { ... } User GetUserByID(int id) { ... } //More Get/Update/Add/Delete methods Is it terrible design to simply make the webservice as secure as I can (not quite sure the way to do something like this yet) and just make a couple methods like this SqlDataReader RunQuery(string sql) { ... } void RunNonQuery(string sql) { ... } I would sorta be like exposing my database to the internet I suppose, which sounds bad but I'm not sure. I just feel like I waste so much time running everything through this webservice, there has to be a quicker yet safe way that doesn't involve my application connecting directly to the database (the application can't connect directly to database because the database isn't open to any connections but localhost, and where the appliction resides the standard sql ports are blocked anyway) Especially when I just need to run a few simple queries

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• How important is index size when searching?

  - by Michael K

  My company has recently began using Apache Solr to search its data. As we learn how to use it we have gone down the path of indexing multiple fields to get the results we need. Most of these are either N-Grammed or Edge-N-Grammed. Gramming by nature takes up a lot of space, which takes more time to search. Space is cheap, but time is less so. Index time is not too important, since a delta-import (only get the changes since last index) is extremely quick and you only pay a penalty on the first import. What we've not been able to determine is what effect the index size has on query times. Obviously a larger index takes longer to search, but the time added by n-gramming a field is difficult to predict. How do you determine whether a field is worth gramming? Can you predict how much longer a query will take when you gram a field?

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• How do you prevent inflation in a virtual economy?

  - by Tetrad

  With your typical MMORPG, players can usually farm the world for raw materials essentially forever. Monsters/mineral veins/etc are usually on some sort of respawn timer, so other than time there really isn't a good way to limit the amount of new currency entering the system. That really only leaves money sinks to try to take money out of the system. What are some strategies to prevent inflation of the in-game currency?

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• How to control messages to the same port from different emitters?

  - by Alex In Paris

  Scene: A company has many factories X, each emits a message to the same receive port in a Biztalk server Y; if all messages are processed without much delay, each will trigger an outgoing message to another system Z. Problem: Sometimes a factory loses its connection for a half-day or more and, when the connection is reestablished, thousands of messages get emitted. Now, the messages still get processed well by Y (Biztalk can easily handle the load) but system Z can't handle the flood and may lock up and severely delay the processing of all other messages from the other X. What is the solution? Creating multiple receive locations that permits us to pause one X or another would lose us information if the factory isn't smart enough to know whether the message was received or not. What is the basic pattern to apply in Biztalk for this problem? Would some throttling parameters help to limit the flow from any one X? Or are their techniques on the end part of Y which I should use instead ? I would prefer this last one since I can be confident that the message box will remember any failures, which could then be resumed.

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• Advice on reconciling discordant data

  - by Justin

  Let me support my question with a quick scenario. We're writing an app for family meal planning. We'll produce daily plans with a target calorie goal and meals to achieve it for our nuclear family. Our calorie goal will be calculated for each person from their attributes (gender, age, weight, activity level). The weight attribute is the simplest example here. When Dad (the fascist nerd who is inflicting this on his family) first uses the application he throws approximate values into it for Daughter. He thinks she is 5'2" (157 cm) and 125 lbs (56kg). The next day Mom sits down to generate the menu and looks back over what the bumbling Dad did, quietly fumes that he can never recall anything about the family, and says the value is really 118 lbs! This is the first introduction of the discord. It seems, in this scenario, Mom is probably more correct that Dad. Though both are only an approximation of the actual value. The next day the dear Daughter decides to use the program and sees her weight listed. With the vanity only a teenager could muster she changes the weight to 110 lbs. Later that day the Mom returns home from a doctor's visit the Daughter needed and decides that it would be a good idea to update her Daughter's weight in the program. Hooray, another value, this time 117 lbs. Now how do you reconcile these data points? Measurement error, confidence in parties, bias, and more all confound the data. In some idealized world we'd have a weight authority of some nature providing the one and only truth. How about in our world though? And the icing on the cake is that this single data point changes over time. How have you guys solved or managed this conflict?

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• Checking timeouts made more readable

  - by Markus

  I have several situations where I need to control timeouts in a technical application. Either in a loop or as a simple check. Of course – handling this is really easy, but none of these is looking cute. To clarify, here is some C# (Pseudo) code: private DateTime girlWentIntoBathroom; girlWentIntoBathroom = DateTime.Now; do { // do something } while (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now); or if (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); Now I was inspired by something a saw in Ruby on StackOverflow: Now I’m wondering if this construct can be made more readable using extension methods. My goal is something that can be read like “If girlWentIntoBathroom is more than 10 seconds ago” 1st attempt if (girlWentIntoBathroom > (10).Seconds().Ago()) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); So I wrote an extension for integer that converts the integer into a TimeSpan public static TimeSpan Seconds(this int amount) { return new TimeSpan(0, 0, amount); } After that, I wrote an extension for TimeSpan like this: public static DateTime Ago(this TimeSpan diff) { return DateTime.Now.Add(-diff); } This works fine so far, but has a great disadvantage. The logic is inverted! Since girlWentIntoBathroom is a timestamp in the past, the right side of the equation needs to count backwards: impossible. Just inverting the equation is no solution, because it will invert the read sentence as well. 2nd attempt So I tried something new: if (girlWentIntoBathroom.IsMoreThan(10).SecondsAgo()) MessageBox.Show("Knock louder"); else MessageBox.Show("Wait a little longer"); IsMoreThan() needs to transport the past timestamp as well as the span for the extension SecondsAgo(). It could be: public static DateWithIntegerSpan IsMoreThan(this DateTime baseTime, int span) { return new DateWithIntegerSpan() { Date = baseTime, Span = span }; } Where DateWithIntegerSpan is simply: public class DateWithIntegerSpan { public DateTime Date {get; set;} public int Span { get; set; } } And SecondsAgo() is public static bool SecondsAgo(this DateWithIntegerSpan dateAndSpan) { return dateAndSpan.Date.Add(new TimeSpan(0, 0, dateAndSpan.Span)) < DateTime.Now; } Using this approach, the English sentence matches the expected behavior. But the disadvantage is, that I need a helping class (DateWithIntegerSpan). Has anyone an idea to make checking timeouts look more cute and closer to a readable sentence? Am I a little too insane thinking about something minor like this?

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• reference list for non-IT driven algorithmic patterns

  - by Quicker

  I am looking for a reference list for non-IT driven algorithmic patterns (which still can be helped with IT implementations of IT). An Example List would be: name; short desc; reference Travelling Salesman; find the shortest possible route on a multiple target path; http://en.wikipedia.org/wiki/Travelling_salesman_problem Ressource Disposition (aka Regulation); Distribute a limited/exceeding input on a given number output receivers based on distribution rules; http://database-programmer.blogspot.de/2010/12/critical-analysis-of-algorithm-sproc.html If there is no such list, but you instantly think of something specific, please 'put it on the desk'. Maybe I can compile something out of the input I get here (actually I am very frustrated as I did not find any such list via research by myself). Details on Scoping: I found it very hard to formulate what I want in a way everything is out that I do not need (which may be the issue why I did not find anything at google). There is a database centric definition for what I am looking for in the section 'Processes' of the second example link. That somehow fits, but the database focus sort of drifts away from the pattern thinking, which I have in mind. So here are my own thoughts around what's in and what's out: I am NOT looking for a foundational algo ref list, which is implemented as basis for any programming language. Eg. the php reference describes substr and strlen. That implements algos, but is not what I am looking for. the problem the algo does address would even exist, if there were no computers (or other IT components) the main focus of the algo is NOT to help other algo's chances are high, that there are implementions of the solution or any workaround without any IT support out there in the world however the algo could be benefitialy implemented/fully supported by a software application = means: the problem of the algo has to be addressed anyway, but running an algo implementation with software automates the process (that is why I posted it on stackoverflow and not somewhere else) typically such algo implementations have more than one input field value and more than one output field value - which implies it could not be implemented as simple function (which is fixed to produce not more than one output value) in a normalized data model often times such algo implementation outputs span accross multiple rows (sometimes multiple tables), whereby the number of output rows depends on the input paraters and rows in the table(s) at start time - which implies that any algo implementation/procedure must interact with a database (read and/or write) I am mainly looking for patterns, not for specific implementations. Example: The Travelling Salesman assumes any coordinates, however it does not say: You need a table targets with fields x and y. - however sometimes descriptions are focussed on examples with specific implementations very much - no worries, as long as the pattern gets clear

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• Validation and authorization in layered architecture

  - by SonOfPirate

  I know you are thinking (or maybe yelling), "not another question asking where validation belongs in a layered architecture?!?" Well, yes, but hopefully this will be a little bit of a different take on the subject. I am a firm believer that validation takes many forms, is context-based and varies at each level of the architecture. That is the basis for the post - helping to identify what type of validation should be performed in each layer. In addition, a question that often comes up is where authorization checks belong. The example scenario comes from an application for a catering business. Periodically during the day, a driver may turn in to the office any excess cash they've accumulated while taking the truck from site to site. The application allows a user to record the 'cash drop' by collecting the driver's ID, and the amount. Here's some skeleton code to illustrate the layers involved: public class CashDropApi // This is in the Service Facade Layer { [WebInvoke(Method = "POST")] public void AddCashDrop(NewCashDropContract contract) { // 1 Service.AddCashDrop(contract.Amount, contract.DriverId); } } public class CashDropService // This is the Application Service in the Domain Layer { public void AddCashDrop(Decimal amount, Int32 driverId) { // 2 CommandBus.Send(new AddCashDropCommand(amount, driverId)); } } internal class AddCashDropCommand // This is a command object in Domain Layer { public AddCashDropCommand(Decimal amount, Int32 driverId) { // 3 Amount = amount; DriverId = driverId; } public Decimal Amount { get; private set; } public Int32 DriverId { get; private set; } } internal class AddCashDropCommandHandler : IHandle<AddCashDropCommand> { internal ICashDropFactory Factory { get; set; } // Set by IoC container internal ICashDropRepository CashDrops { get; set; } // Set by IoC container internal IEmployeeRepository Employees { get; set; } // Set by IoC container public void Handle(AddCashDropCommand command) { // 4 var driver = Employees.GetById(command.DriverId); // 5 var authorizedBy = CurrentUser as Employee; // 6 var cashDrop = Factory.CreateCashDrop(command.Amount, driver, authorizedBy); // 7 CashDrops.Add(cashDrop); } } public class CashDropFactory { public CashDrop CreateCashDrop(Decimal amount, Employee driver, Employee authorizedBy) { // 8 return new CashDrop(amount, driver, authorizedBy, DateTime.Now); } } public class CashDrop // The domain object (entity) { public CashDrop(Decimal amount, Employee driver, Employee authorizedBy, DateTime at) { // 9 ... } } public class CashDropRepository // The implementation is in the Data Access Layer { public void Add(CashDrop item) { // 10 ... } } I've indicated 10 locations where I've seen validation checks placed in code. My question is what checks you would, if any, be performing at each given the following business rules (along with standard checks for length, range, format, type, etc): The amount of the cash drop must be greater than zero. The cash drop must have a valid Driver. The current user must be authorized to add cash drops (current user is not the driver). Please share your thoughts, how you have or would approach this scenario and the reasons for your choices.

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• Advice: should I focus on PHP + MySQL, or split my time for more JS and CSS? [closed]

  - by fakaff

  I started learning web development about three months ago (in between working my regular job), and I'm finally starting to get some vague, distant notion of understanding. I find the server-side stuff the most interesting; though I've not gone anywhere near Apache quite yet, which I assume will be necessary at some point. As cool as toying around with visuals and UI is, programming and database stuff inspires me with new ideas and possibilities every minute (I've even bought, on a whim, a wonderfully dry bunch of books on database theory and relational algebra). And whatever CSS or Javascript tutorial I'm doing, it often feels like a distraction from the PHP/MySQL stuff I'd rather be playing with. For someone like me who's just starting out, which is the most advisable course of action? (in terms of being marketable as a programmer): To focus on PHP and SQL stuff exclusively, and only once I master those to diversify my skills. To first learn all three (PHP/MySQL, Javascript, CSS and design) and only once I'm fluent in all three focus on PHP and databases?

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• Are null references really a bad thing?

  - by Tim Goodman

  I've heard it said that the inclusion of null references in programming languages is the "billion dollar mistake". But why? Sure, they can cause NullReferenceExceptions, but so what? Any element of the language can be a source of errors if used improperly. And what's the alternative? I suppose instead of saying this: Customer c = Customer.GetByLastName("Goodman"); // returns null if not found if (c != null) { Console.WriteLine(c.FirstName + " " + c.LastName + " is awesome!"); } else { Console.WriteLine("There was no customer named Goodman. How lame!"); } You could say this: if (Customer.ExistsWithLastName("Goodman")) { Customer c = Customer.GetByLastName("Goodman") // throws error if not found Console.WriteLine(c.FirstName + " " + c.LastName + " is awesome!"); } else { Console.WriteLine("There was no customer named Goodman. How lame!"); } But how is that better? Either way, if you forget to check that the customer exists, you get an exception. I suppose that a CustomerNotFoundException is a bit easier to debug than a NullReferenceException by virtue of being more descriptive. Is that all there is to it?

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• What kind of graphics would you like better? [ pictures ] [closed]

  - by Roger Travis

  I am looking forward to make an android game, something angrybirds style. I've already made my own engine and now have to decide what kind of graphics should I make. It could be either realistic, like that or a doodle-style like this Right now the first one looks more appealing to me... on the other hand, doodle-graphics are very easy to draw and their transparency doesn't seem to slow down the engine much. What do you think?

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• Should I force users to update an application?

  - by Brian Green

  I'm writing an application for a medium sized company that will be used by about 90% of our employees and our clients. In planning for the future we decided to add functionality that will verify that the version of the program that is running is a version that we still support. Currently the application will forcequit if the version is not among our supported versions. Here is my concern. Hypothetically, in version 2.0.0.1 method "A" crashes and burns in glorious fashion and method "B" works just fine. We release 2.0.0.2 to fix method A and deprecate version 0.1. Now if someone is running 0.1 to use method B they will be forced to update to fix something that isn't an issue for them right now. My question is, will the time saved not troubleshooting old, unsupported versions outweigh the cost in usability?

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• Should i continue my self-taught coding practice or learn how to do coding professionally?

  - by G1i1ch

  Lately I've been getting professional work, hanging out with other programmers, and making friends in the industry. The only thing is I'm 100% self-taught. It's caused my style to extremely deviate from the style of those that are properly trained. It's the techniques and organization of my code that's different. It's a mixture of several things I do. I tend to blend several programming paradigms together. Like Functional and OO. I lean to the Functional side more than OO, but I see the use of OO when something would make more sense as an abstract entity. Like a game object. Next I also go the simple route when doing something. When in contrast, it seems like sometimes the code I see from professional programmers is complicated for the sake of it! I use lots of closures. And lastly, I'm not the best commenter. I find it easier just to read through my code than reading the comment. And most cases I just end up reading the code even if there are comments. Plus I've been told that, because of how simply I write my code, it's very easy to read it. I hear professionally trained programmers go on and on about things like unit tests. Something I've never used before so I haven't even the faintest idea of what they are or how they work. Lots and lots of underscores "_", which aren't really my taste. Most of the techniques I use are straight from me, or a few books I've read. Don't know anything about MVC, I've heard a lot about it though with things like backbone.js. I think it's a way to organize an application. It just confuses me though because by now I've made my own organizational structures. It's a bit of a pain. I can't use template applications at all when learning something new like with Ubuntu's Quickly. I have trouble understanding code that I can tell is from someone trained. Complete OO programming really leaves a bad taste in my mouth, yet that seems to be what EVERYONE else is strictly using. It's left me not that confident in the look of my code, or wondering whether I'll cause sparks when joining a company or maybe contributing to open source projects. In fact I'm rather scared of the fact that people will eventually be checking out my code. Is this just something normal any programmer goes through or should I really look to change up my techniques?

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• When decomposing a large function, how can I avoid the complexity from the extra subfunctions?

  - by missingno

  Say I have a large function like the following: function do_lots_of_stuff(){ { //subpart 1 ... } ... { //subpart N ... } } a common pattern is to decompose it into subfunctions function do_lots_of_stuff(){ subpart_1(...) subpart_2(...) ... subpart_N(...) } I usually find that decomposition has two main advantages: The decomposed function becomes much smaller. This can help people read it without getting lost in the details. Parameters have to be explicitly passed to the underlying subfunctions, instead of being implicitly available by just being in scope. This can help readability and modularity in some situations. However, I also find that decomposition has some disadvantages: There are no guarantees that the subfunctions "belong" to do_lots_of_stuff so there is nothing stopping someone from accidentally calling them from a wrong place. A module's complexity grows quadratically with the number of functions we add to it. (There are more possible ways for things to call each other) Therefore: Are there useful convention or coding styles that help me balance the pros and cons of function decomposition or should I just use an editor with code folding and call it a day? EDIT: This problem also applies to functional code (although in a less pressing manner). For example, in a functional setting we would have the subparts be returning values that are combined in the end and the decomposition problem of having lots of subfunctions being able to use each other is still present. We can't always assume that the problem domain will be able to be modeled on just some small simple types with just a few highly orthogonal functions. There will always be complicated algorithms or long lists of business rules that we still want to correctly be able to deal with. function do_lots_of_stuff(){ p1 = subpart_1() p2 = subpart_2() pN = subpart_N() return assembleStuff(p1, p2, ..., pN) }

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• 3D mobile game development [on hold]

  - by SCM

  I am not a developer or programmer and, I am planning an educative project that will involve having students to develop a cross-platform, 3D mobile game, similar to the SimCity concept. I need to write a project requirement and I'd like to pick someone's brain to understand what's involved in developing such a project: -Is it realistic to have one or two students to do it? and along their other modules at uni? - How much time can it take to develop from scratch? - what are the different skills required? Thank you All SCM

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• Is this a pattern? Should it be?

  - by Arkadiy

  The following is more of a statement than a question - it describes something that may be a pattern. The question is: is this a known pattern? Or, if it's not, should it be? I've had a situation where I had to iterate over two dissimilar multi-layer data structures and copy information from one to the other. Depending on particular use case, I had around eight different kinds of layers, combined in about eight different combinations: A-B-C B-C A-C D-E A-D-E and so on After a few unsuccessful attempts to factor out the repetition of per-layer iteration code, I realized that the key difficulty in this refactoring was the fact that the bottom level needed access to data gathered at higher levels. To explicitly accommodate this requirement, I introduced IterationContext class with a number of get() and set() methods for accumulating the necessary information. In the end, I had the following class structure: class Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const = 0; }; class RecursingIterator : public Iterator { RecursingIterator(const Iterator &below); }; class IterateOverA : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // Iterate over members in dataStructure1 // locate corresponding item in dataStructure2 (passed via context) // and set it in the context // invoke the sub-iterator }; class IterateOverB : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // iterate over members dataStructure2 (form context) // set dataStructure2's item in the context // locate corresponding item in dataStructure2 (passed via context) // invoke the sub-iterator }; void main() { class FinalCopy : public Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // copy data from structure 1 to structure 2 in the context, // using some data from higher levels as needed } } IterationContext ctx(dateStructure2); IterateOverA(IterateOverB(FinalCopy())).iterate(dataStructure1, ctx); } It so happens that dataStructure1 is a uniform data structure, similar to XML DOM in that respect, while dataStructure2 is a legacy data structure made of various structs and arrays. This allows me to pass dataStructure1 outside of the context for convenience. In general, either side of the iteration or both sides may be passed via context, as convenient. The key situation points are: complicated code that needs to be invoked in "layers", with multiple combinations of layer types possible at the bottom layer, the information from top layers needs to be visible. The key implementation points are: use of context class to access the data from all levels of iteration complicated iteration code encapsulated in implementation of pure virtual function two interfaces - one aware of underlying iterator, one not aware of it. use of const & to simplify the usage syntax.

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• Designing a user-defined list to be stored in a relational database - Should I include user index?

  - by Zaemz

  By index, I mean, as the user creates the list, each item receives an integer index for its place in that particular list. Since there will be a table of ListItems, I'd prefer to avoid using the name "Index" for the field. Then I was thinking - should I even include the list index in the database? I figured I would because the list would be created in the same fashion every time, then. Or I could order the list for the user based on its actual primary key, since the list items are created in succession anyway... What should I do?

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• Logic or Algorithm to solve this problem [closed]

  - by jade

  I have two lists. List1 {a,b,c,d,e} and List2 {f,g,h,i,j} The relation between the two list is as follows a->g,a->h,h->c,h->d,d->i,d->j Now I have these two lists displayed. Based on the relation above on selecting element a from List1, List2 shows g,h. On selecting h from List2, in List1 c,d are shown in List1. On selecting d from List1 it shows i,j in List2. How to trace back to initial state by deselecting the elements in reverse order in which they have been selected?

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