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  • Liskov substitution and abstract classes / strategy pattern

    - by Kolyunya
    I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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  • How to motivate team for knowledge sharing sessions

    - by ring bearer
    I work in a team with wide range of expertise and experience. I have been trying to introduce weekly knowledge sharing sessions. Sessions of 30-60 min length where everybody gets a chance to present something and talk about it. This will contribute in improving presentational and language skills. However, the team is not motivated towards this, either the attendance is too low or none. How to get a team work towards such an idea?

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  • What is your most preferred method of site pagination?

    - by John Smith
    There seem to be quite a few implementations of this feature. Some sites like like Stackexchange have it laid out like this: [1][2][3][4][5] ... [954][Next] Other sites like game forums may have something like this: [1][2][3] ... [10] ... [50] ... [500] ... [954][Next] Some sites like webcomics (XKCD comes to mind) have it laid out like this: [Last][Prev][Random][Next][First] Reddit has a very simple pagination with only: [Prev][Next] Sites like Stackexchange and Google also allow you to change how many results you want per page. Personally, I have never used this feature. Is it even worth including or does it just further confuse the design with needless features? Personally, I have only ever seen the need for the webcomic style (without the random). If I need to go to a specific page (which is very, very rare) then I can just edit the address bar. Is it good design to make something more complex for rare occasions where it might make save the user some time? Is having to edit the address bar to navigate the site effectively in some circumstances bad design?

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  • Design for future changes or solve the problem at hand.

    - by Naveen
    While writing the code or during design do you try to generalize the problem at the first instance itself or try to solve that very specific problem. I am asking this because, trying to generalize the problem tends to complicate the things (which may not be necessary) and on the otherhand it will be very difficult to extend the specific solution if there is a change in the requirement. I guess the solution is to find the middle path which is easier said than done. How do you tackle this type of problem ? If you start generalizing it at what point of time you know that this much of generalization is sufficient ?

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  • How do you answer "Rate yourself" questions?

    - by Vinoth Kumar
    Hi , I have been frequently asked questions like "Rate yourself in java" It goes like interviewer : Rate yourself in java on the scale of 10 me: 9 interviewer : Rate yourself in J2EE me : 8 .... But really I just come up with arbitrary numbers. Sure I know Java well , but what does it mean to say "9 out of 10" . I think it is a very subjective question, that does not make sense overall. The problem is ,if I say 9 , If I am not able to answer any question , the interviewer might think , "this guy just said 9" . On the other hand If I said 6 , there is a good chance the interviewer might think "He rates himself this low...not good" How do you respond to such questions ?

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  • Relationships in a Chen ERD

    - by Nibroc A Rehpotsirhc
    I am working on a Chen ERD to model our organizations merchandise. Our central entity is a Style. We have supplemental entities of Color and Season. I am defining our assortment as the relationship between these three entities, and this relationship itself will have attributes and is defined by the three entities which participate in the mandatory relationship. The rules are; Many Styles can be offered in a Season, and a Style can be offered in many Seasons. Within a Season, a Style can be offered in Many Colors. I then have 2 other entities, one of which I believe is a weak entity, Climate, and the other may be weak, but I am not sure, this being Transaction Channel. I am thinking of these as relationships off of a relationship? Meaning, for a given Style/Color combination offered in a Season, it can be available through 1 or more Transaction Channels. Additionally, within a season, a given Style/Color combination can be intended for 1 or more Climates. Is it valid to have relationships off of relationships? Or does this requirement dictate that I should think of this Style/Color/Season relationship as an entity itself, and define the relationships to Climate and Transaction Channel off of this entity?

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  • Does it make sense to write a build scripts in C++?

    - by Klaim
    I'm using CMake to generate my projects IDE/makefiles, but I still need to call custom "scripts" to manipulate my compiled files or even generate code. In previous projects I've been using Python and it was OK, but now I'm having serious trouble managing a lot of dependencies in two very big projects I'm working on so I want to minimize the dependencies everywhere. Someone suggested to me to use C++ to write my build scripts instead of adding a language dependency just for that. The projects themeselves already use C++ so there are several advantages that I can see: to build the whole project, only a C++ compiler and CMake would be necessary, nothing else (all the other dependencies are C or C++); C++ type safety (when using modern C++) makes everything easier to get "correct"; it's also the language I know the better so I'm more at ease with it even if I'm able to write some good Python code; potential gain in execution speed (but i don't think it will really be perceptible); However, I think there might be some drawbacks and I'm not sure of the real impact as I didn't try yet: might be longer to write the code (that said I'm not sure because I'm efficient enough in C++ to write something that work quickly, so maybe for this system it wouldn't be so long to write) (compilation time shouldn't be a problem for this case); I must assume that all the text files I'll read as input are in UTF-8, I'm not sure it can be easilly checked at runtime in C++ and the language will not check it for you; libraries in C++ are harder to manage than in scripting languages; I lack experience and forsight so maybe I'm missing advantages and drawbacks. So the question is: does it make sense to use C++ for this? do you have experiences to report and do you see advantages and disadvantages that might be important?

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  • How are you using CFThread in ColdFusion Applications?

    - by marc esher
    I'm presenting on Concurrency in ColdFusion at CFObjective this year, and I'd like to hear how you're using CFThread in your ColdFusion applications. In addition, what problems have you had while using it, and how (if at all) have you solved them? What do you dislike about CFThread? Have you run into significant weaknesses with CFThread or other problems where it simply could not do what you wanted to do? Finally, if there's anything you'd like to add related to concurrency in CF, not specifically related to CFThread, please do tell.

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  • How do I start correctly in building database classes in c#?

    - by e4rthdog
    I am new in C# programming and in OOP. I need to dive into web applications for my company, and I need to do it fast and correct. So even that I know ASP.NET MVC is the way to go, I want to start with some simple applications with ASP.NET Webforms and then advance to MVC logic. Also regarding my db classes: I plan to create common database classes in order to be able to use them either from WinForms or ASP.NET applications. I also know that the way to go is to learn about ORM and EF. BUT I also want to start from where I am feeling comfortable and that is the traditional ADO.NET way. So about my Data Access Layer classes: Should I return my results in datasets or arraylists/lists? Should my methods do their own connect/disconnect from the db, or have separate methods and let the application maintain the connection?

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  • Finish feature reverted commits from develop

    - by marco-fiset
    I am using git as a version control system, and using git-flow as the branching model. I started a feature branch some weeks ago in order to maintain the system in a clean state while developping that feature. The main development continued on the develop branch, and changes from develop were merged periodically into the feature, to keep it up to date as much as possible. However came the time where the feature was finished, and I used git-flow's finish feature to merge the feature back into develop. The merge was successfully done, but then I found out that some of the commits I made in develop were reverted by the merge commit! Nowhere in develop or in the feature branch were these changes reverted, I can't see any commit that overwrote them. I just can't find anything. The only theory I have for the moment is that git is failing on me, but that would be extremely unlikely. Maybe I did some kind of wrong manipulation that made this situation come true? I can trace back in the history when the commit was made. I can see that the changes from that commit were reverted by the merge commit. Nowhere in the branch I see a commit that reverts those changes. Yet they were reverted. How is this even possible?

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  • Where do service implementations fit into the Microsoft Application Architecture guidelines?

    - by tuespetre
    The guidelines discuss the service layer with its service interfaces and data/message/fault contracts. They also discuss the business layer with its logic/workflow components and entities as well as the 'optional' application facade. What is unclear still to me after studying this guide is where the implementations of the service interfaces belong. Does the application facade in the business layer implement these interfaces, or does a separate 'service facade' exist to make calls to the business layer and it's facade/raw components? (With the former, there would be less seemingly trivial calls to yet another layer, though with the latter I could see how the service layer could remove the concerns of translating business entities to data contracts from the business layer.)

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  • Logging errors caused by exceptions deep in the application

    - by Kaleb Pederson
    What are best-practices for logging deep within an application's source? Is it bad practice to have multiple event log entries for a single error? For example, let's say that I have an ETL system whose transform step involves: a transformer, pipeline, processing algorithm, and processing engine. In brief, the transformer takes in an input file, parses out records, and sends the records through the pipeline. The pipeline aggregates the results of the processing algorithm (which could do serial or parallel processing). The processing algorithm sends each record through one or more processing engines. So, I have at least four levels: Transformer - Pipeline - Algorithm - Engine. My code might then look something like the following: class Transformer { void Process(InputSource input) { try { var inRecords = _parser.Parse(input.Stream); var outRecords = _pipeline.Transform(inRecords); } catch (Exception ex) { var inner = new ProcessException(input, ex); _logger.Error("Unable to parse source " + input.Name, inner); throw inner; } } } class Pipeline { IEnumerable<Result> Transform(IEnumerable<Record> records) { // NOTE: no try/catch as I have no useful information to provide // at this point in the process var results = _algorithm.Process(records); // examine and do useful things with results return results; } } class Algorithm { IEnumerable<Result> Process(IEnumerable<Record> records) { var results = new List<Result>(); foreach (var engine in Engines) { foreach (var record in records) { try { engine.Process(record); } catch (Exception ex) { var inner = new EngineProcessingException(engine, record, ex); _logger.Error("Engine {0} unable to parse record {1}", engine, record); throw inner; } } } } } class Engine { Result Process(Record record) { for (int i=0; i<record.SubRecords.Count; ++i) { try { Validate(record.subRecords[i]); } catch (Exception ex) { var inner = new RecordValidationException(record, i, ex); _logger.Error( "Validation of subrecord {0} failed for record {1}", i, record ); } } } } There's a few important things to notice: A single error at the deepest level causes three log entries (ugly? DOS?) Thrown exceptions contain all important and useful information Logging only happens when failure to do so would cause loss of useful information at a lower level. Thoughts and concerns: I don't like having so many log entries for each error I don't want to lose important, useful data; the exceptions contain all the important but the stacktrace is typically the only thing displayed besides the message. I can log at different levels (e.g., warning, informational) The higher level classes should be completely unaware of the structure of the lower-level exceptions (which may change as the different implementations are replaced). The information available at higher levels should not be passed to the lower levels. So, to restate the main questions: What are best-practices for logging deep within an application's source? Is it bad practice to have multiple event log entries for a single error?

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  • Why is there a "new" in Go?

    - by dystroy
    I'm still puzzled as why we have new in Go. When you want to instantiate a struct, you do t := Thing{} and, obviously, you can get a pointer to a new instance by doing t := &Thing{} But there's also this possibility : t := new(Thing) This last one seems a little alien to me. &Thing{} is as clear and concise as new(Thing) and it uses only constructs you often use elsewhere. It's also more extensible as you might change it to &Thing{3} or &Thing{Feets:7}. In my opinion, having a supplementary keyword is costly, it makes the language more complex and adds to what you must know. And it might mask to newcomers what's behind instantiating a struct. It also makes one more reserved word. So what's the reasoning behind new ? Is it something useful ? Should we use it ?

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  • Is "White-Board-Coding" inappropriate during interviews?

    - by Eoin Campbell
    This is a somewhat subjective quesiton but I'd love to hear feedback/opinions from either interviewers/interviewees on the topic. We split our technical part into 4 parts. Write Code, Read & Analyse Code, Design Session & Code on the white board. For the last part what we ask interviewees to do is write a small code snippet (4-5 lines) on the whiteboard and explain as they go through it. Let me be clear the purpose is not to catch people out. We're not looking for perfect syntax. Hell it can even be pseudo-code. but the point is to give them a very simple problem and see if their brain can communicate the solution to us. By simple problems I mean "Reverse a string", "FizzBuzz" etc... EDIT Just with regards the comment about Pseudo-Code. We always ask for an explicit language first. We;re a .NET C# house. we've only said "pseudo-code" where someone has been blanking/really struggling with the code. My question is "Is it innappropriate / unreasonable to expect a programmer to write a code snippet on a whiteboard during an interview ?"

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  • Reading mp3 metadata?

    - by Blaze
    I am planing on writing an application using Vala. Its purposed is to import mp3 files from a location and rename them if necessary. The renaming information should be provided by the ID3 tags in the mp3 file such as the title and the number of the song. My target platform is Ubuntu (Linux). As the question says, I am searching for how can I achieve this on Vala. I think this functionality might be provided by Gstreamer.

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  • What tools are available for remote communication when working from home or with a distributed team?

    - by Ryan Hayes
    My supervisor is allowing my team to dip our toes in the water of working from home. Considering a recent aquisition of another company is requiring some employees to love this new idea which will hack up to an hour off their commute into work every morning, I really want this to succeed. In order to make it a success, we need good tools to make our lives a lot easier. We currently are set up with OpenVPN, and Team Foundation Server 2010 with SharePoint 2010, and use Live Messenger (for SharePoint integration and easier remote desktop) for IM. These are just what we use (and they are currently working well) , but you can suggest other products. So, what are some great tools that will helps us collaborate, communicate, and generally work together when we're hours apart?

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  • What to Return with Async CRUD methods

    - by RualStorge
    While there is a similar question focused on Java, I've been in debates with utilizing Task objects. What's the best way to handle returns on CRUD methods (and similar)? Common returns we've seen over the years are: Void (no return unless there is an exception) Boolean (True on Success, False on Failure, exception on unhandled failure) Int or GUID (Return the newly created objects Id, 0 or null on failure, exception on unhandled failure) The updated Object (exception on failure) Result Object (Object that houses the manipulated object's ID, Boolean or status field to with success or failure indicated, Exception information if there was one, etc) The concern comes into play as we've started moving over to utilizing C# 5's Async functionality, and this brought the question up of how we should handle CRUD returns large-scale. In our systems we have a little of everything in regards to what we return, we want to make these returns standardized... Now the question is what is the recommended standard? Is there even a recommended standard yet? (I realize we need to decide our standard, but typically we do so by looking at best practices, see if it makes sense for us and go from there, but here we're not finding much to work with)

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  • Eyes easily get dry and itchy [closed]

    - by Lo Wai Lun
    I have currently working as a programmer for half a year Very often, I often looking the monitors with natural contrast and brightness. Still when the weather is getting cold, my eyes feel dry and itchy. Sometimes I can see some red 'tree-roots' (capillaries) near iris. At home, i sometimes use my notebook for 13" or Galaxy Nexus Brightness are also natural contrast and brightness , a bit dim How should we take care of our eyes under this scenario?

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  • API Design Techniques

    - by Dehumanizer
    Is it right or more beautiful to name the functions with an prefix, like in Qt? Or using "many" namespaces, but 'normal' names for functions? For example, slOpenFile(); //"sl" means "some lib" vs some_lib::file_functions::openFile(); UPD: I've read somewhere that the first variant(using some prefix) is better, because the API users can perform 'fast' search among the documentation and in the Internet. E.g. by typing the magic prefix search engine starts to advice the exact functions. Is it enough to use the first variant?

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  • Changes in Language Punctuation [closed]

    - by Wes Miller
    More social curiosity than actual programming question... (I got shot for posting this on Stack Overflow. They sent me here. At least i hope here is where they meant.) Based on the few responses I got before the content police ran me off Stack Overflow, I should note that I am legally blind and neatness and consistency in programming are my best friends. A thousand years ago when I took my first programming class (Fortran 66) and a mere 500 years ago when I tokk my first C and C++ classes, there were some pretty standard punctuation practices across languages. I saw them in Basic (shudder), PL/1, PL/AS, Rexx even Pascal. Ok, APL2 is not part of this discussion. Each language has its own peculiar punctuation. Pascal's periods, Fortran's comma separated do loops, almost everybody else's semicolons. As I learned it, each language also has KEYWORDS (if, for, do, while, until, etc.) which are set off by whitespace (or the left margin) if, etc. Each language has function, subroutines of whatever they're called. Some built-in some user coded. They were set off by function_name( parameters );. As in sqrt( x ) or rand( y ); Lately, there seems to be a new set of punctuation rules. Especially in c++ where initializers get glued onto the end of variable declarations int x(0); or auto_ptr p(new gizmo); This usually, briefly fools me into thinking someone is declaring a function prototype or using a function as a integer. Then "if" and 'for' seems to have grown parens; if(true) for(;;), etc. Since when did keywords become functions. I realize some people think they ARE functions with iterators as parameters. But if "for" is a function, where did the arg separating commas go? And finally, functions seem to have shed their parens; sqrt (2) select (...) I know, I koow, loosening whitespace rules is good. Keep reading. Question: when did the old ways disappear and this new way come into vogue? Does anyone besides me find it irritating to read and that the information that the placement of punctuation used to convey is gone? I know full well that K&R put the { at the end of the "if" or "for" to save a byte here and there. Can't use that excuse here. Space as an excuse for loss of readability died as HDD space soared past 100 MiB. Your thoughts are solicited. If there is a good reason to do this, I'll gladly learn it and maybe in another 50 years I'll get used to it. Of course it's good that compilers recognize these (IMHO) typos and keep right on going, but just because you CAN code it that way doesn't mean you HAVE to, right?

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  • Avoiding Object Oriented Pitfalls, Migrating from C, What Worked for You?

    - by Stephen
    I've been programming in procedural languages for quite some time now, and my first reaction to a problem is to start breaking it down into tasks to perform rather than to consider the different entities (objects) that exist and their relationships. I have had a university course in OOP, and understand the fundamentals of encapsulation, data abstraction, polymorphism, modularity and inheritance. I read Learning to think in the Object Oriented Way and Learning object oriented thinking, and will be looking at some of the books pointed to in those answers. I think that several of my medium to large sized projects will benefit from effective use of OOP but as a novice I would like to avoid time consuming, common errors. Based on your experiences, what are these pitfalls and what are reasonable ways around them? If you could explain why they are pitfalls, and how your suggestion is effective in addressing the issue it'd be appreciated. I'm thinking along the lines of something like "Is it common to have a fair number of observer and modifier methods and use private variables or are there techniques for consolidating/reducing them?" I'm not worried about using C++ as a pure OO language, if there are good reasons to mix methods. (Reminiscent of the reasons to use GOTOs, albeit sparingly.) Thank you!

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  • Is it worth it to switch from home-grown remote command interface to using JMX

    - by Sam Goldberg
    Without knowing too much about JMX, I've always assumed that it would be the best approach for building in remote management to our standalone Java server application. Our server application has some minimal remote control capability, using text commands sent via TCP/IP socket to it. Using the home grown approach, it is fairly to add a new command. (Just create new command text, and the code to handle that in the message receiver). On the other hand, we have hardly implemented any commands, even though there are many things we would like to be able to execute remotely. I am trying to weigh the value of moving to incorporating JMX (learning it, and building the interfaces), versus just sticking with the home-grown approach. Does anyone have any experience or advice regarding changing an existing application to use JMX?

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  • Embedded Model Designing -- top down or bottom up?

    - by Jeff
    I am trying to learn RoR and develop a webapp. I have a few models I have thought of for this app, and they are fairly embedded. For example (please excuse my lack of RoR syntax): Model: textbook title:string type:string has_many: chapters Model: chapter content:text has_one: review_section Model: review_section title:string has_many: questions has_many: answers , through :questions Model: questions ... Model: answers ... My question is, with the example I gave, should I start at the top model (textbook) or the bottom most (answers)?

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  • What types of programming contest problems are there?

    - by Alex
    Basically, I want to make a great reference for use with programming contests that would have all of the algorithms that I can put together that I would need during a contest as well as sample useage for the code. I'm planning on making this into a sort of book that I could print off and take with me to competitions. I would like to do this rather than simply bringing other books (such as Algorithms books) because I think that I will learn a lot more by going over all of the algorithms myself as well as I would know exactly what I have in the book, making it more efficient to have and use. So, I've been doing research to determine what types of programming problems and algorithms are common on contests, and the only thing I can really find is this (which I have seen referenced a few times): Hal Burch conducted an analysis over spring break of 1999 and made an amazing discovery: there are only 16 types of programming contest problems! Furthermore, the top several comprise almost 80% of the problems seen at the IOI. Here they are: Dynamic Programming Greedy Complete Search Flood Fill Shortest Path Recursive Search Techniques Minimum Spanning Tree Knapsack Computational Geometry Network Flow Eulerian Path Two-Dimensional Convex Hull BigNums Heuristic Search Approximate Search Ad Hoc Problems The most challenging problems are Combination Problems which involve a loop (combinations, subsets, etc.) around one of the above algorithms - or even a loop of one algorithm with another inside it. These seem extraordinarily tricky to get right, even though conceptually they are ``obvious''. Now that's good and all, but that study was conducted in 1999, which was 13 years ago! One thing I know is that there are no BigNums problems any more (as Java has a BigInteger class, they have stopped making those problems). So, I'm wondering if anyone knows of any more recent studies of the types of problems that may be seen in a programming contest? Or what the most helpful algorithms on contests would be?

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  • Where can you find your first customers as a freelancer?

    - by Adam Smith
    I want to start doing freelance work, but no matter how I look at it, it seems like the best way to get customers and to have work most of the time, you have to already be in the freelancing game. Most freelancers I've talked to have had the same customers over the years or got new customers because their satisfied clients referred them. What I'd like to know from the successful people here that work as freelancers is how do you start doing business when you haven't yet set foot in freelancing? I want to start small, creating websites that won't require me to hire other people other than maybe a designer I already know. (I'd like to create desktop applications as well, but I think I should keep that for later when I'm more experienced) . I thought about localized Google ads or visiting companies and meeting the people in charge there, but I wouldn't know which kind of businesses to look for or if it's even a good way to approach this. Anyone care to share their personal startup experiences / advice that can help future freelancers?

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