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  • Is there a design pattern for chained observers?

    - by sharakan
    Several times, I've found myself in a situation where I want to add functionality to an existing Observer-Observable relationship. For example, let's say I have an Observable class called PriceFeed, instances of which are created by a variety of PriceSources. Observers on this are notified whenever the underlying PriceSource updates the PriceFeed with a new price. Now I want to add a feature that allows a (temporary) override to be set on the PriceFeed. The PriceSource should still update prices on the PriceFeed, but for as long as the override is set, whenever a consumer asks PriceFeed for it's current value, it should get the override. The way I did this was to introduce a new OverrideablePriceFeed that is itself both an Observer and an Observable, and that decorates the actual PriceFeed. It's implementation of .getPrice() is straight from Chain of Responsibility, but how about the handling of Observable events? When an override is set or cleared, it should issue it's own event to Observers, as well as forwarding events from the underlying PriceFeed. I think of this as some kind of a chained observer, and was curious if there's a more definitive description of a similar pattern.

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  • Starting a career in mobile development in next 5 months?

    - by Jungle Hunter
    I will be starting my career shortly and have the opportunity to being my career in mobility. I have an option to be in more traditional fields (the ones that have been around for quite some time now like web development and Java apps development). What are the pros and cons of both? Also, if I do choose mobility, then I might be presented with the option of iOS or Android. Pros and cons of choosing each? Period: Joining in next 5 months. Mobility company profile: Major consulting company.

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  • New code base, what experiences/recommendations do you have?

    - by hlovdal
    I will later this year start on a project (embedded hardware, C, small company) where I believe that most (if not all) code will be new. So what experiences do you have to share as advice to starting a new code base? What have you been missing in projects that you have been working on? What has worked really well? What has not worked? Let's limit this question to be about things that relate directly to the code (e.g "banning the use of gets()": in scope, version control: border line, build system: out of scope).

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  • responsibility for storage

    - by Stefano Borini
    A colleague and I were brainstorming about where to put the responsibility of an object to store itself on the disk in our own file format. There are basically two choices: object.store(file) fileformatWriter.store(object) The first one gives the responsibility of serialization on the disk to the object itself. This is similar to the approach used by python pickle. The second groups the representation responsibility on a file format writer object. The data object is just a plain data container (eventually with additional methods not relevant for storage). We agreed on the second methodology, because it centralizes the writing logic from generic data. We also have cases of objects implementing complex logic that need to store info while the logic is in progress. For these cases, the fileformatwriter object can be passed and used as a delegate, calling storage operations on it. With the first pattern, the complex logic object would instead accept the raw file, and implement the writing logic itself. The first method, however, has the advantage that the object knows how to write and read itself from any file containing it, which may also be convenient. I would like to hear your opinion before starting a rather complex refactoring.

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  • Requirements/issue tracker similar to online spreadsheet

    - by Maxim Eliseev
    Is there a requirements/issue tracker software which is similar to Google spreadsheet? We have Fogbugz but I find it more heavyweight and slow than a simple spreadsheet. Is there a Fogbugz alternative which is - fast - can show issues/requirements as a spreadsheet (at) and allows in-place editing - supports tree structures (where issue can have child issues)? It is required for a small project. There will be 2 developers and 1-2 other users. I guess that only one user will be actively maintaining it. UPDATE I do not say that a spreadsheet is better than Fogbugz or similar tools. In fact I am looking for a tool which is similar to Fogbugz and could replace a spreadsheet, but faster than Fogbugz and has an additional feature (table-like mode). I'd like to find a tool which can operate in a mode which looks like a table (one row per issue) but has a rich set features (similar to Fogbugs and JIRA). I find Fogbugz (and similar tools) inconvenient because I must enter the web form in order to edit anything. In-place editing (when issues are shown as a table) would be much faster.

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  • Drawing shapes dynamically on an image through web browser

    - by Tom Beech
    We have a scenario where we create floor plans of locations when we visit. The floor plan is finally shown on the web. It's come to the point now where we want to show floor plans but have a key with various items on them, when an item on the key is clicked, the image should highlight all the areas of the floorplan that have that specific item. I guess we're looking for some sort of open standard javascript lib to deal with SVG (has to work pre IE9 so pure SVG wont cut it) and the floor plans have to be able to be created through a .net application to be deployed on the web. I'd rather stay away from flash if at all possible to be honest. Below are a few conceptual images of what we're trying to achieve.

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  • Is throwing an error in unpredictable subclass-specific circumstances a violation of LSP?

    - by Motti Strom
    Say, I wanted to create a Java List<String> (see spec) implementation that uses a complex subsystem, such as a database or file system, for its store so that it becomes a simple persistent collection rather than an basic in-memory one. (We're limiting it specifically to a List of Strings for the purposes of discussion, but it could extended to automatically de-/serialise any object, with some help. We can also provide persistent Sets, Maps and so on in this way too.) So here's a skeleton implementation: class DbBackedList implements List<String> { private DbBackedList() {} /** Returns a list, possibly non-empty */ public static getList() { return new DbBackedList(); } public String get(int index) { return Db.getTable().getRow(i).asString(); // may throw DbExceptions! } // add(String), add(int, String), etc. ... } My problem lies with the fact that the underlying DB API may encounter connection errors that are not specified in the List interface that it should throw. My problem is whether this violates Liskov's Substitution Principle (LSP). Bob Martin actually gives an example of a PersistentSet in his paper on LSP that violates LSP. The difference is that his newly-specified Exception there is determined by the inserted value and so is strengthening the precondition. In my case the connection/read error is unpredictable and due to external factors and so is not technically a new precondition, merely an error of circumstance, perhaps like OutOfMemoryError which can occur even when unspecified. In normal circumstances, the new Error/Exception might never be thrown. (The caller could catch if it is aware of the possibility, just as a memory-restricted Java program might specifically catch OOME.) Is this therefore a valid argument for throwing an extra error and can I still claim to be a valid java.util.List (or pick your SDK/language/collection in general) and not in violation of LSP? If this does indeed violate LSP and thus not practically usable, I have provided two less-palatable alternative solutions as answers that you can comment on, see below. Footnote: Use Cases In the simplest case, the goal is to provide a familiar interface for cases when (say) a database is just being used as a persistent list, and allow regular List operations such as search, subList and iteration. Another, more adventurous, use-case is as a slot-in replacement for libraries that work with basic Lists, e.g if we have a third-party task queue that usually works with a plain List: new TaskWorkQueue(new ArrayList<String>()).start() which is susceptible to losing all it's queue in event of a crash, if we just replace this with: new TaskWorkQueue(new DbBackedList()).start() we get a instant persistence and the ability to share the tasks amongst more than one machine. In either case, we could either handle connection/read exceptions that are thrown, perhaps retrying the connection/read first, or allow them to throw and crash the program (e.g. if we can't change the TaskWorkQueue code).

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  • Is defining every method/state per object in a series of UML diagrams representative of MDA in general?

    - by Max
    I am currently working on a project where we use a framework that combines code generation and ORM together with UML to develop software. Methods are added to UML classes and are generated into partial classes where "stuff happens". For example, an UML class "Content" could have the method DeleteFromFileSystem(void). Which could be implemented like this: public partial class Content { public void DeleteFromFileSystem() { File.Delete(...); } } All methods are designed like this. Everything happens in these gargantuan logic-bomb domain classes. Is this how MDA or DDD or similar usually is done? For now my impression of MDA/DDD (which this has been called by higherups) is that it severely stunts my productivity (everything must be done The Way) and that it hinders maintenance work since all logic are roped, entrenched, interspersed into the mentioned gargantuan bombs. Please refrain from interpreting this as a rant - I am merely curious if this is typical MDA or some sort of extreme MDA UPDATE Concerning the example above, in my opinion Content shouldn't handle deleting itself as such. What if we change from local storage to Amazon S3, in that case we would have to reimplement this functionality scattered over multiple places instead of one single interface which we can provide a second implementation for.

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  • How to learn the math behind the code?

    - by Solomon Wise
    I am a 12 year old who has recently gotten into programming. (Although I know that the number of books you have read does not determine your programming competency or ability, just to paint a "map" of where I am in terms of the content I know...) I've finished the books: Python 3 For Absolute Beginners Pro Python Python Standard Library by Example Beautiful Code Agile Web Development With Rails and am about halfway into Programming Ruby. I have written many small programs (One that finds which files have been updated and deleted in a directory, one that compares multiple players' fantasy baseball value, and some text based games, and many more). Obviously, as I'm not some sort of child prodigy, I can't take a formal Computer Science course until high school. I really want to learn computer science to increase my knowledge about the code, and the how the code runs. I've really become interested in the math part after reading the source code for Python's random module. Is there a place where I can learn CS, or programming math online for free, at a level that would be at least partially understandable to a person my age?

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  • What would a database look like if it were normalized to be completely abstracted? lets call it Max(n) normal form

    - by Doug Chamberlain
    edit: By simplest form i was not implying that it would be easy to understand. For instance, developing in low level assembly language is the simplest way to can develop code, but it is far from the easiest. Essentially, what I am asking is in math you can simplify a fraction to a point where it can no longer be simplfied. Can the same be true for a database and what would a database look like in its simplest, form?

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  • How can I select an appropriate licensing/obfuscation system for .NET?

    - by Adam
    I saw someone suggesting .NET Reactor once as a good obfuscator. I went to their website to check it out and saw they have a product called IntelliLock which is advertised as a pretty robust licensing system which has code protection/obfuscation built in. With that said, I tried to contact them and ask them a few questions regarding the product, but have not had any response. This is kind of a red flag for me. However, it seems like there is some user base for this product whom are satisfied. What .NET licensing system(s) with .NET code protection/obfuscation are you using? What are its pros & cons that you have encountered? Are there things I should be looking for or looking to avoid when evaluating these systems?

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  • Solution with multiple projects and (GitHub) single issue tracker and repository

    - by Luiz Damim
    I have a Visual Studio solution with multiple projects: Acme.Core Acme.Core.Tests Acme.UI.MvcSite1 Acme.UI.MvcSite2 Acme.UI.WinformsApp1 Acme.UI.WinformsApp2 ... The entire solution is checked-in in a single GitHub (private) repo. Acme.Core contains our business logic and all UI projects are deployables. UI projects have different requirements and features, but some of them are implemented in more than one project. All issues are opened in a single issue tracker and classified using labels ([MvcSite1], [WinformsApp1], etc) but I'm thinking it's starting to get messy. Is it ok to use a single repository and issue tracker to track multiple projects in one solution?

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  • Object-Oriented Operating System

    - by nmagerko
    As I thought about writing an operating system, I came across a point that I really couldn't figure out on my own: Can an operating system truly be written in an Object-Oriented Programming (OOP) Language? Being that these types of languages do not allow for direct accessing of memory, wouldn't this make it impossible for a developer to write an entire operating system using only an OOP Language? Take, for example, the Android Operating System that runs many phones and some tablets in use around the world. I believe that this operating system uses only Java, an Object-Oriented language. In Java, I have been unsuccessful in trying to point at and manipulate a specific memory address that the run-time environment (JRE) has not assigned to my program implicitly. In C, C++, and other non-OOP languages, I can do this in a few lines. So this makes me question whether or not an operating system can be written in an OOP, especially Java. Any counterexamples or other information is appreciated.

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  • Design Application to "Actively" Invite Users (pretend they have privileges)

    - by user3086451
    I am designing an application where users message one another privately, and may send messages to any Entity in the database (an Entity may not have a user account yet, it is a professional database). I am not sure how to best design the database and the API to allow messaging unregistered users. The application should remain secure, and data only accessed by those with correct permissions. Messages sent to persons without user accounts serve as an invitation. The invited person should be able to view the message, act on it, and complete the user registration upon receiving an InviteMessage. In simple terms, I have: User misc user fields (email, pw, dateJoined) Entity (large professional dataset): personalDetails... user->User (may be null) UserMessage: sender->User recipient->User dateCreated messageContent, other fields..... InviteMessage: sender->User recipient->Entity expiringUrl inviteeEmail inviteePhone I plan to alert the user when selecting a recipient that is not registered yet, and inform that he may send the message as an invitation by providing email, phone where we can send the invitation. Invitations will have a unique, one-time-use URL, e.g. uuid.uuid4(). When accessed, the invitee will see the InviteMessage and details about completing his/her registration profile. When registration is complete, InviteMessage details to a new instance of UserMessage (to not lose their data), and assign it to the newly created User. The ability to interact with and invite persons who do not yet have accounts is a key feature of the application, and it seems better to separate the invitation from the private, app messages (easier to keep functionality separate, better if data model changes). Is this a reasonable, good design? If not, what would you suggest? Do you have any improvements? Am I correct to choose to create a separate endpoint for creating invitations via the API?

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  • Is it worth to learn programming for windows?

    - by Herr Kaleun
    as a programmer, i was skeptical about (Microsoft) desktop software back in the early 2000s (i was a kid then) and yet, i was right. So i advanced to PHP in 2004 and began working on Web applications. When i look at the software world today, i really can't understand, how software for Microsoft or call it, "windows" should have a future. Is it still worth, learning it? I have a strong feeling that, in about 3-4 years, mac will have the dominance in the Personal Computer market. If i am wrong, please correct me. Thanks!

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  • How many questions is it appropriate to ask as an intern?

    - by Casey Patton
    So, I just started an internship, and I'm worried that I'm asking too many questions. I've been assigned a mentor who has been assigning me projects and helping me learn all the company's technologies and methodologies. However, there's so much new material for me to learn while doing this project that I have a lot of questions. I generally ask questions over instant messages or E-mail (those are the primary modes of communication for my company). I'm trying to be careful not to ask too many questions: I don't want to come off as annoying or dumb. How many questions is appropriate to ask? Once an hour? More? Less? Keep in mind, my mentor is also a fellow programmer that has his own responsibilities.

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  • cygwin GNU make .net program piping inconsistent behavior

    - by Codism
    This question may sound like a superuser question but I feel there is something related to programming. Anyway, my computer had a fresh installation of Win 7 64 and cygwin recently. Now I observed some problem with pipe handling in gnu make file. The following is the Makefile I use to reproduce the issue: all: fsutil | cat my-dotnet-console.exe | cat The problem is: for the first command line, the piping works every time but for the second command line, the piping barely works - I got no result for the second command for most cases, regardless of the environment (cmd or bash) in which the make file is invoked. However, if I copy paste the second command line into cmd (or bash), the pipe works every time. The following is my .net program: static void Main(string[] args) { Console.WriteLine(new string('a', 40)); Console.Out.Flush(); } The make version is 3.82.90 but the same problem was observed in a previous version (because of the windows path handling problem in 3.82.9, I replaced make.exe with a previous version). I don't know the exact cygwin version I have installed but the current version on cygwin.com is 1.7.11-1. Currently, my work around is to redirect the output to a temporary file but it would be great if I can avoid the temporary file. Thanks

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  • Why is C++ predominant in programming contests and competitions?

    - by daniels
    I understand that C++ is a very fast language, but ain't C just as fast, or faster in some cases? Then you might say that C++ has OOP, but the amount of OOP you need for most programming puzzles is not that big, and in my opinion C would be able handle that. Here's why I am asking this: I am very interested in programming contests and competitions, and I am used to coding in C on those. However, I noticed that the vast majority of people use C++ (e.g., 17 out of 25 finalists on Google Code Jam 2011 used it, while no one used C), so I am wondering if I am at a disadvantage going with C. Apart from the Object Orientation, what makes C++ a more suitable language for programming competitions? What are the features of the language I should learn and use to perform better on the competitions? For background, I consider myself pretty proficient in C, but I am just starting to learn C++.

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  • How can I implement a Epub Reader in Javascript

    - by Vlad Nicula
    I'm wondering if I can create a epub reader in javascript. The basic requirements would be: 1) Server parts of the epub reader from a server API. 2) Read the EPUB data in javascript. 3) Render it on page. 4) Provide some extra functionality, like text highlights or page notes. I have no information about how I could do this. I'm willing to try a prototype project. What are the steps that I could take towards implementing such a thing?

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  • When does 'optimizing code' == 'structuring data'?

    - by NewAlexandria
    A recent article by ycombinator lists a comment with principles of a great programmer. #7. Good programmer: I optimize code. Better programmer: I structure data. Best programmer: What's the difference? Acknowledging subjective and contentious concepts - does anyone have a position on what this means? I do, but I'd like to edit this question later with my thoughts so-as not to predispose the answers.

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  • What is a generic term for name/identifier? (as opposed to label)

    - by d3vid
    I need to refer to a number of things that have both an identifier value (used in code and configuration), and a human-readable label. These things include: database columns dropdown items subapplications objects stored in a dictionary I want two unambiguous terms. One to refer to the identifier/value/key. One to refer to the label. As you can see, I'm pretty settled on the latter :) For the former, identifier seems best (not everything is strictly a key, and value and name could refer to the label; although, identifier usually refers only to a variable name), but I would prefer to follow an established practice if there is one. Is there an established term for this? (Please provide a source.) If not, are there any examples of a choice from a significant source (Java APIs, MSDN, a big FLOSS project)? (I wasn't sure if this should be posted here or to English Language & Usage. I thought this was the more appropriate expert audience. Happy to migrate if not.)

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  • How can one manage thousands of IF...THEN...ELSE rules?

    - by David
    I am considering building an application, which, at its core, would consist of thousands of if...then...else statements. The purpose of the application is to be able to predict how cows move around in any landscape. They are affected by things like the sun, wind, food source, sudden events etc. How can such an application be managed? I imagine that after a few hundred IF-statements, it would be as good as unpredictable how the program would react and debugging what lead to a certain reaction would mean that one would have to traverse the whole IF-statement tree every time. I have read a bit about rules engines, but I do not see how they would get around this complexity.

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  • White box testing with Google Test

    - by Daemin
    I've been trying out using GoogleTest for my C++ hobby project, and I need to test the internals of a component (hence white box testing). At my previous work we just made the test classes friends of the class being tested. But with Google Test that doesn't work as each test is given its own unique class, derived from the fixture class if specified, and friend-ness doesn't transfer to derived classes. Initially I created a test proxy class that is friends with the tested class. It contains a pointer to an instance of the tested class and provides methods for the required, but hidden, members. This worked for a simple class, but now I'm up to testing a tree class with an internal private node class, of which I need to access and mess with. I'm just wondering if anyone using the GoogleTest library has done any white box testing and if they have any hints or helpful constructs that would make this easier. Ok, I've found the FRIEND_TEST macro defined in the documentation, as well as some hints on how to test private code in the advanced guide. But apart from having a huge amount of friend declerations (i.e. one FRIEND_TEST for each test), is there an easier idion to use, or should I abandon using GoogleTest and move to a different test framework?

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  • Subsumption architecture vs. perceptual control theory

    - by Yasir G.
    I'm a new person to AI field and I have to research and compare 2 different architectures for a thesis I'm writing. Before you scream (homework thread), I've been reading on these 2 topics only to find that I'm confusing myself more.. let me first start with stating briefly what I know so far. Subsumption is based on the fact that targets of a system are different in sophistication, thus that requires them to be added as layers, each layer can suppress (modify) the command of the layers below it, and there are inhibitors to stop signals from execution lets say. PCT stresses on the fact that there are nodes to handle environmental changes (negative feedback), so the inputs coming from an environment go through a comparator node and then an action is generated by that node, HPCT or (Hierarchical PCT) is based on nesting these cycles inside each other so a small cycle to avoid crashing would be nested in a more sophisticated cycle that targets a certain location for example. My questions, am I getting this the right way? am I missing any critical understanding about these 2 models? also any idea where I can find simplified explanations for each theory (so far been struggling trying to understand the papers from Google scholar :< ) /Y

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  • Notifying a separate application of an event

    - by TomDestry
    I have an application that runs through various tasks as an automated process. My client would like me to create a file in a given folder for each task as a way to flag when each task completes. They prefer this to a database flag because they can be notified by the file system rather than continually polling a database table. I can do this but creating and deleting files as flags feels clunky. Is there a more elegant approach to notifying a third-party of an event?

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