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  • Breaking 1NF to model subset constraints. Does this sound sane?

    - by Chris Travers
    My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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  • Inheritance vs composition in this example

    - by Gerenuk
    I'm wondering about the differences between inheritance and composition examined with concrete code relevant arguments. In particular my example was Inheritance: class Do: def do(self): self.doA() self.doB() def doA(self): pass def doB(self): pass class MyDo(Do): def doA(self): print("A") def doB(self): print("B") x=MyDo() vs Composition: class Do: def __init__(self, a, b): self.a=a self.b=b def do(self): self.a.do() self.b.do() x=Do(DoA(), DoB()) (Note for composition I'm missing code so it's not actually shorter) Can you name particular advantages of one or the other? I'm think of: composition is useful if you plan to reuse DoA() in another context inheritance seems easier; no additional references/variables/initialization method doA can access internal variable (be it a good or bad thing :) ) inheritance groups logic A and B together; even though you could equally introduce a grouped delegate object inheritance provides a preset class for the users; with composition you'd have to encapsule the initialization in a factory so that the user does have to assemble the logic and the skeleton ... Basically I'd like to examine the implications of inheritance vs composition. I heard often composition is prefered, but I'd like to understand that by example. Of course I can always start with one and refactor later to the other.

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  • Should I cache the data or hit the database?

    - by JD01
    I have not worked with any caching mechanisms and was wondering what my options are in the .net world for the following scenario. We basically have a a REST Service where the user passes an ID of a Category (think folder) and this category may have lots of sub categories and each of the sub categories could have 1000 of media containers (think file reference objects) which contain information about a file that may be on a NAS or SAN server (files are videos in this case). The relationship between these categories is stored in a database together with some permission rules and meta data about the sub categories. So from a UI perspective we have a lazy loaded tree control which is driven by the user by clicking on each sub folder (think of Windows explorer). Once they come to a URL of the video file, they then can watch the video. The number of users could grow into the 1000s and the sub categories and videos could be in the 10000s as the system grows. The question is should we carry on the way it is currently working where each request hits the database or should we think about caching the data? We are on using IIS 6/7 and Asp.net.

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  • What is the best wrapping strategy ?

    - by Riduidel
    Hi, I'm planning to integrate an external tool (ffmpeg in my particular case, but it could be anything, in fact, as lolng as its tasks are long running ones). This tool has a lot of command-line parameters. For now, I've done to simple things with it, already requiring me a good bunch of class writing, to embed all the information it can return to me. I now face the even more complex task of having to send it a bunch of parameters and to handle possible errors. So, what is a best way for that ? Create classes containing all possible options Relying upon a reverse equivalent of commons-cli / CliBuilder / OptionParser Directly write all options from user input Obiwan Kenobi powers (or anything I don't even know about) Please notice I do it in an uncommon language (for the sake of me, don't ask me what it is, as it looks like a desperate and sterile union between CoffeeScript and lua), as a consequence, there can be no framework doing what I want in the language I use.

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  • What should a game have in order to keep humans playing it?

    - by Adam Davis
    In many entertainment professions there suggestions, loose rules, or general frameworks one follows that appeal to humans in one way or another. For instance, many movies and books follow the monomyth. In video games I find many types of games that attract people in different ways. Some are addicted to facebook gem matching games. Others can't get enough of FPS games. Once in awhile, though, you find a game that seems to transcend stereotypes and appeals almost immediately to everyone that plays it. For instance, Plants Versus Zombies seems to have a very, very large demographic of players. There are other games similar in reach. I'm curious what books, blogs, etc there are that explore these game types and styles, and tries to suss out one or more popular frameworks/styles that satisfy people, while keeping them coming back for more.

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  • Access functions from user control without events?

    - by BornToCode
    I have an application made with usercontrols and a function on main form that removes the previous user controls and shows the desired usercontrol centered and tweaked: public void DisplayControl(UserControl uControl) I find it much easier to make this function static or access this function by reference from the user control, like this: MainForm mainform_functions = (MainForm)Parent; mainform_functions.DisplayControl(uc_a); You probably think it's a sin to access a function in mainform, from the usercontrol, however, raising an event seems much more complex in such case - I'll give a simple example - let's say I raise an event from usercontrol_A to show usercontrol_B on mainform, so I write this: uc_a.show_uc_b+= (s,e) => { usercontrol_B uc_b = new usercontrol_B(); DisplayControl(uc_b); }; Now what if I want usercontrol_B to also have an event to show usercontrol_C? now it would look like this: uc_a.show_uc_b+= (s,e) => { usercontrol_B uc_b = new usercontrol_B(); DisplayControl(uc_b); uc_b.show_uc_c += (s2,e2) => {usercontrol_C uc_c = new usercontrol_C(); DisplayControl(uc_c);} }; THIS LOOKS AWFUL! The code is much simpler and readable when you actually access the function from the usercontrol itself, therefore I came to the conclusion that in such case it's not so terrible if I break the rules and not use events for such general function, I also think that a readable usercontrol that you need to make small adjustments for another app is preferable than a 100% 'generic' one which makes my code look like a pile of mud. What is your opinion? Am I mistaken?

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  • When would you want two references to the same object?

    - by HCBPshenanigans
    In Java specifically, but likely in other languages as well; When would it be useful to have two references to the same object? Example: Dog a = new Dog(); Dob b = a; Is there a situation where this would be useful? Why would this be a preferred solution to using a whenever you want to interact with the object represented by a? Edit: Can I just say that all of your dog related examples are Delightful!

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  • can you have too many dto/bo - mapping method

    - by Fredou
    I have a windows service, 2 web services and a web interface that need to follow the same path (data wise). So I came up with two ways of creating my solution. My concern is the fact that the UI/WS/etc will have their own kind of DTO (let's say the model in ASP.Net MVC) that should be mapped to a DTO so the SL can then map it to a BO then mapping it to the proper EF6 DTO so that I can save it in a database. So I'm thinking of doing it this way to remove one level of mapping. Which one should I take? Or is there a 3rd solution?

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  • Updating an Entity through a Service

    - by GeorgeK
    I'm separating my software into three main layers (maybe tiers would be a better term): Presentation ('Views') Business logic ('Services' and 'Repositories') Data access ('Entities' (e.g. ActiveRecords)) What do I have now? In Presentation, I use read-only access to Entities, returned from Repositories or Services, to display data. $banks = $banksRegistryService->getBanksRepository()->getBanksByCity( $city ); $banksViewModel = new PaginatedList( $banks ); // some way to display banks; // example, not real code I find this approach quite efficient in terms of performance and code maintanability and still safe as long as all write operations (create, update, delete) are preformed through a Service: namespace Service\BankRegistry; use Service\AbstractDatabaseService; use Service\IBankRegistryService; use Model\BankRegistry\Bank; class Service extends AbstractDatabaseService implements IBankRegistryService { /** * Registers a new Bank * * @param string $name Bank's name * @param string $bik Bank's Identification Code * @param string $correspondent_account Bank's correspondent account * * @return Bank */ public function registerBank( $name, $bik, $correspondent_account ) { $bank = new Bank(); $bank -> setName( $name ) -> setBik( $bik ) -> setCorrespondentAccount( $correspondent_account ); if( null === $this->getBanksRepository()->getDefaultBank() ) $this->setDefaultBank( $bank ); $this->getEntityManager()->persist( $bank ); return $bank; } /** * Makes the $bank system's default bank * * @param Bank $bank * @return IBankRegistryService */ public function setDefaultBank( Bank $bank ) { $default_bank = $this->getBanksRepository()->getDefaultBank(); if( null !== $default_bank ) $default_bank->setDefault( false ); $bank->setDefault( true ); return $this; } } Where am I stuck? I'm struggling about how to update certain fields in Bank Entity. Bad solution #1: Making a series of setters in Service for each setter in Bank; - seems to be quite reduntant, increases Service interface complexity and proportionally decreases it's simplicity - something to avoid if you care about code maitainability. I try to follow KISS and DRY principles. Bad solution #2: Modifying Bank directly through it's native setters; - really bad. If you'll ever need to move modification into the Service, it will be pain. Business logic should remain in Business logic layer. Plus, there are plans on logging all of the actions and maybe even involve user permissions (perhaps, through decorators) in future, so all modifications should be made only through the Service. Possible good solution: Creating an updateBank( Bank $bank, $array_of_fields_to_update) method; - makes the interface as simple as possible, but there is a problem: one should not try to manually set isDefault flag on a Bank, this operation should be performed through setDefaultBank method. It gets even worse when you have relations that you don't want to be directly modified. Of course, you can just limit the fields that can be modified by this method, but how do you tell method's user what they can and cannot modify? Exceptions?

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  • Game ideas for a platformer

    - by user5925
    I have created a platformer which currently has the features listed below. I would greatly appreciate any further ideas which I could implement! (I don't play a lot of games which is why I require help) -- Walking/jumping/movement -- player can shoot lasers -- enemies also walk, fly, and shoot lasers -- water (you can swim in this) -- mud (slows you down on contact, and stops you from jumping) -- ladders -- damage when falling from a large height, unless falling into water -- moving platforms -- springboards (jumping on them shoot you into the air) -- growing platforms (allow you to reach new places) -- key and door system -- gem and coin collection system

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  • Code Smell: Inheritance Abuse

    - by dsimcha
    It's been generally accepted in the OO community that one should "favor composition over inheritance". On the other hand, inheritance does provide both polymorphism and a straightforward, terse way of delegating everything to a base class unless explicitly overridden and is therefore extremely convenient and useful. Delegation can often (though not always) be verbose and brittle. The most obvious and IMHO surest sign of inheritance abuse is violation of the Liskov Substitution Principle. What are some other signs that inheritance is The Wrong Tool for the Job even if it seems convenient?

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  • How URL Redirection affects SEO?

    - by Costa
    The following paragraph is from SEO Google Guide Google is good at crawling all types of URL structures, even if they're quite complex, but spending the time to make your URLs as simple as possible for both users and search engines can help. Some webmasters try to achieve this by rewriting their dynamic URLs to static ones; while Google is fine with this, we'd like to note that this is an advanced procedure and if done incorrectly, could cause crawling issues with your site. What makes URL re-writing implementation incorrect for GoogleBot? I am using Asp.net 3.5 framework. Thanks

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  • Presenting Loading Data Warehouse Partitions with SSIS 2012 at SQL Saturday DC!

    - by andyleonard
    Join Darryll Petrancuri and me as we present Loading Data Warehouse Partitions with SSIS 2012 Saturday 8 Dec 2012 at SQL Saturday 173 in DC ! SQL Server 2012 table partitions offer powerful Big Data solutions to the Data Warehouse ETL Developer. In this presentation, Darryll Petrancuri and Andy Leonard demonstrate one approach to loading partitioned tables and managing the partitions using SSIS 2012, and reporting partition metrics using SSRS 2012. Objectives A practical solution for loading Big...(read more)

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  • Algorithmic Forecasting and Pattern Recognition

    - by Ryan King
    Say a user could enter project data into my software. Each project has 2 variables "size" and "work" and they're related but the relationship is not known. Is there a way to programmatically determine the relationship between the variables based on previous data and forecast the amount of work provided if only given the size of the project in the future? For Example, say the user had manually entered the following projects. Project 1 - Size:1, Work: 4 Project 2 - Size:2, Work: 7 Project 3 - Size:3, Work: 10 Project 4 - Size:4, Work: x What should I look into to be able to programmatically determine, that Work = Size*3+1 and therefor be able to say that x=13?

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  • Architecture Best Practice (MVC): Repository Returns Object & Object Member Accessed Directly or Repository Returns Object Member

    - by coderabbi
    Architecturally speaking, which is the preferable approach (and why)? $validation_date = $users_repository->getUser($user_id)->validation_date; Seems to violate Law of Demeter by accessing member of object returned by method call Seems to violate Encapsulation by accessing object member directly $validation_date = $users_repository->getUserValidationDate($user_id); Seems to violate Single Responsibility Principle as $users_repository no longer just returns User objects

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  • Constructor should generally not call methods

    - by Stefano Borini
    I described to a colleague why a constructor calling a method can be an antipattern. example (in my rusty C++) class C { public : C(int foo); void setFoo(int foo); private: int foo; } C::C(int foo) { setFoo(foo); } void C::setFoo(int foo) { this->foo = foo } I would like to motivate better this fact through your additional contribute. If you have examples, book references, blog pages, or names of principles, they would be very welcome. Edit: I'm talking in general, but we are coding in python.

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  • Which is a better practice - helper methods as instance or static?

    - by Ilian Pinzon
    This question is subjective but I was just curious how most programmers approach this. The sample below is in pseudo-C# but this should apply to Java, C++, and other OOP languages as well. Anyway, when writing helper methods in my classes, I tend to declare them as static and just pass the fields if the helper method needs them. For example, given the code below, I prefer to use Method Call #2. class Foo { Bar _bar; public void DoSomethingWithBar() { // Method Call #1. DoSomethingWithBarImpl(); // Method Call #2. DoSomethingWithBarImpl(_bar); } private void DoSomethingWithBarImpl() { _bar.DoSomething(); } private static void DoSomethingWithBarImpl(Bar bar) { bar.DoSomething(); } } My reason for doing this is that it makes it clear (to my eyes at least) that the helper method has a possible side-effect on other objects - even without reading its implementation. I find that I can quickly grok methods that use this practice and thus help me in debugging things. Which do you prefer to do in your own code and what are your reasons for doing so?

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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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  • Any technical references for game-oriented icons and symbols?

    - by willc2
    To make localizing easier, I'm using icons to show in-game information like achievements and bonuses. Coming up with good designs isn't easy, especially when it has to be integrated into the rest of the game's art style. Can I do better than looking at some random selection of existing games? Are there any reference books or sites that cover game graphics specifically? I'm looking for more theory and best-practices rather than pre-made graphics.

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  • What would most games benefit from having?

    - by Phil
    I think I've seen "questions" like this on stackoverflow but sorry if I'm overstepping any bounds. Inspired by my recent question and all the nice answers (Checklist for finished game?) I think every gamedev out there has something he/she thinks that almost every game should have. That knowledge is welcome here! So this is probably going to be an inspirational subjective list of some sorts and the point is that anyone reading this question will see a point or two that they've overlooked in their own development and might benefit from adding. I think a good example might be: "some sort of manual or help section. Of course it should be proportional to how advanced the game is. Some users won't need it and won't go looking for it but the other ones that do will become very frustrated if they can't remember how to do something specific that should be in the manual". A bad example might be "good gameplay". Of course every game benefits from this but the answer is not very helpful.

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  • Desktop application, dependency injection

    - by liori
    I am thinking of applying a real dependency injection library to my toy C#/GTK# desktop application. I chose NInject, but I think this is irrelevant to my question. There is a database object, a main window and several utility window classes. It's clear that I can inject the database into every window object, so here DI is useful. But does it make sense to inject utility window classes into other window classes? Example: I have classes such as: class MainWindow {…} class AddItemWindow {…} class AddAttachmentWindow {…} class BrowseItemsWindow {…} class QueryBuilderWindow {…} class QueryBrowserWindow {…} class PreferencesWindow {…} … Each of the utility classes can be opened from MainWindow. Some utility windows can also be opened from other utility windows. Generally, there might be a really complex graph of who can open whom. So each of those classes might need quite a lot of other window classes injected. I'm worried that such usage will go against the suggestion not to inject too many classes at once and become a code smell. Should I use some kind of a service locator object here?

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  • The danger of changing the domain of your portfolio

    - by Mervin
    So I have a online portfolio that is available at mervin-ux-portfolio.com but I am planning to change hosts since the current host I am hosting it with is hitting me with a very high yearly renewal rate. When I was inquiring about domain transfers ,,they told me that since I had not initiated the domain transfer within 14 days of the expiry of the domain ,they cannot do it immediately and it would take about two weeks to to release the domain name. Since I dont like the idea of my site being down for like 2 weeks ,I was wondering if I should start afresh with a new domain on a new host and what were the potential dangers of that ( I have the entire site backup,so creating a replica of the site on the new host wont be hard) I also wont be losing any business or work since I work full time currently but I was just wondering about the challenges in terms of getting my domain name back to the top of search results and basically getting it out there assuming I go the new domain name approach. I know this is strictly not an UX question but I was hoping people could give some suggestions on what I should do

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  • Making Class Diagram for MVC Pattern Project

    - by iMohammad
    I have a question about making a class diagram for an MVC based college senior project. If we have 2 actors of users in my system, lets say Undergrad and Graduate students are the children of abstract class called User. (Generalisation) Each actor has his own features. My question, in such case, do we need to have these two actors in separate classes which inherits from the abstract class User? even though, I'm going to implement them as roles using one Model called User Model ? I think you can see my confusion here. I code using MVC pattern, but I've never made a class diagram for this pattern. Thank you in advance!

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  • Anti aliasing problem

    - by byronyasgur
    I am auditioning fonts on google web fonts and one that I was discounting was Ubuntu because it looked a bit jagged ( screenshot below taken straight from google); however afterward I read an article where it was mentioned as a good choice, and there was a screenshot where it looked really good ( to me anyway ). I am using windows 7 and have tried looking at it in chrome and firefox. I notice the same thing with some other fonts but this one is a good example because it looks perfect in the screenshot but not so good when I look at it on their site. I know this essentially is a question about setting my computer, but I thought that this would be the best place to pose the question: Is there something wrong with the settings on my machine seeing as it's obviously not showing the font the same on my computer as it did when the article writer downloaded it and used it in an image. The screenshot from Google ... The screenshot from the article above ...

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  • Programming Language vs. Game Engine [on hold]

    - by hunteroatway17
    I understand that this question has been asked multiple times before. I am just asking this quick and simple question. I have been learning programming in C#, Java and C++ for the past 6 months; Just experimenting with each. I think that C++ is the one that I like most. What I would like to know and am wondering about is should I learn a programming language and use a 2D framework like Allegro; Or should I learn Unity and make 2D games in that because it is probably faster and easier. I want to learn something that I can get pretty good at, seeing as I am pursuing a career in indie game development. I also have a programmer's mind set and I am a left brain thinker so learning a language is not a issue. I just want to best and most future proof choice. Thanks.

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