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  • Perl : In splice() type of arg1 must be array, cannot be scalar dereference. How to fix?

    - by Michael Mao
    I am trying to comprehend the reference/dereference system in Perl. What I am trying to do is to remove an element by using reference: my $ref= \@{$collection{$_[0]}}; # delete($$ref[$i]); # delete works, I've tested that already splice($$ref, $i, 1); # this wouldn't do. I first tried the delete() subroutine, it works; however, it doesn't shift the index after the removed elements forward by 1, so I cannot continue working on other stuff. I then Googled and found the splice() subroutine which does delete and shift in one go. But the error feedback tells me that "Type of arg 1 to splice must be array (not scalar dereference)..." I then tried something like this: splice(@{$$ref}, $i, 1); That resulted in another error like this: "Not a SCALAR reference at...(pointing at that line)" So I am a bit puzzled, how could I handle this issue? I prefer not using any CPAN or additional library for the solution, if possible.

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  • C++ - Distributing different headers than development

    - by Ben
    I was curious about doing this in C++: Lets say I have a small library that I distribute to my users. I give my clients both the binary and the associated header files that they need. For example, lets assume the following header is used in development: #include <string> ClassA { public: bool setString(const std::string & str); private: std::string str; }; Now for my question. For deployment, is there anything fundamentally wrong with me giving a 'reduced' header to my clients? For example, could I strip off the private section and simply give them this: #include <string> ClassA { public: bool setString(const std::string & str); }; My gut instinct says "yes, this is possible, but there are gotchas", so that is why I am asking this question here. If this is possible and also safe, it looks like a great way to hide private variables, and thus even avoid forward declaration in some cases. I am aware that the symbols will still be there in the binary itself, and that this is just a visibility thing at the source code level. Thanks!

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  • Bizzare Java invalid Assignment Operator Error

    - by Kay
    public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; private static final int defaultInitialCapacity = 25; public void add(T newItem) throws HeapException{ if (lastIndex < Max_Heap){ heap[lastIndex] = newItem; int place = lastIndex; int parent = (place – 1)/2; //ERROR HERE********** while ( (parent >=0) && (heap[place].compareTo(heap[parent])>0)){ T temp = heap[place]; heap[place] = heap[parent]; heap[parent] = temp; place = parent; parent = (place-1)/2; }else { throw new HeapException(“HeapException: Heap full”); } } } Eclipse complains that there is a: "Syntax error on token "Invalid Character", invalid AssignmentOperator" With the red line beneath the '(place-1)' There shouldn't be an error at all since it's just straight-forward arithmetic. Or is it not that simple?

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  • Refactoring. Your way to reduce code complexity of big class with big methods

    - by Andrew Florko
    I have a legacy class that is rahter complex to maintain: class OldClass { method1(arg1, arg2) { ... 200 lines of code ... } method2(arg1) { ... 200 lines of code ... } ... method20(arg1, arg2, arg3) { ... 200 lines of code ... } } methods are huge, unstructured and repetitive (developer loved copy/paste aprroach). I want to split each method into 3-5 small functions, whith one pulic method and several helpers. What will you suggest? Several ideas come to my mind: Add several private helper methods to each method and join them in #region (straight-forward refactoring) Use Command pattern (one command class per OldClass method in a separate file). Create helper static class per method with one public method & several private helper methods. OldClass methods delegate implementation to appropriate static class (very similiar to commands). ? Thank you in advance!

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  • Entity Framework Decorator Pattern

    - by Anthony Compton
    In my line of business we have Products. These products can be modified by a user by adding Modifications to them. Modifications can do things such as alter the price and alter properties of the Product. This, to me, seems to fit the Decorator pattern perfectly. Now, envision a database in which Products exist in one table and Modifications exist in another table and the database is hooked up to my app through the Entity Framework. How would I go about getting the Product objects and the Modification objects to implement the same interface so that I could use them interchangeably? For instance, the kind of things I would like to be able to do: Given a Modification object, call .GetNumThings(), which would then return the number of things in the original object, plus or minus the number of things added by the modification. This question may be stemming from a pretty serious lack of exposure to the nitty-gritty of EF (all of my experience so far has been pretty straight-forward LOB Silverlight apps), and if that's the case, please feel free to tell me to RTFM. Thanks in advance!

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  • Fundamentals of Deserialization in .NET?

    - by Codehelp
    I have been working with XML for past couple of months with .NET Basically all the work I do involve XML in oneway of another so I thought it would be good to learn the serialization and deserialization part of the game. My work mostly involves the 'Deserialization' part of it. Almost every time I have an XML file which has to be used by the application that I write. An object form of the XML is the best way to use. Now initially the XML was very straight forward, just a couple of tags which would translate into a class very easily using XSD.exe tool. Things grew a bit complex with nesting of tags and I found Xsd2Code gen tool work fine. During this whole process I have been able to do my work with a lot of help from Stackoverflow community, thanks for that, but I think I have missed the forest for the trees. I need to know how Deserialization works in .NET Fundamentally, I would like to know what happens behind the scenes in taking a XML and converting it into a usable object. Code samples have helped me in the past, and as mentioned earlier the problem get's solved but the learning does not happen. So, if anyone can guide to resources that can get me started on the Deserialization part of the game, I would be thankful to them. Regards.

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  • Fixing an SQL where statement that is ugly and confusing

    - by Mike Wills
    I am directly querying the back-end MS SQL Server for a software package. The key field (vehicle number) is defined as alpha though we are entering numeric value in the field. There is only one exception to this, we place an "R" before the number when the vehicle is being retired (which means we sold it or the vehicle is junked). Assuming the users do this right, we should not run into a problem using this method. (Right or wrong isn't the issue here) Fast forward to now. I am trying to query a subset of these vehicle numbers (800 - 899) for some special processing. By doing a range of '800' to '899' we also get 80, 81, etc. If I cast the vehicle number into an INT, I should be able to get the right range. Except that these "R" vehicles are kicking me in the butt now. I have tried where vehicleId not like 'R%' and cast(vehicleId as int) between 800 and 899 however, I get a casting error on one of these "R" vehicles. What does work is where vehicleId not between '800' and '899' and cast(vehicleId as int) between 800 and 899', but I feel there has to be a better way and less confusing way. I have also tried other variations with HAVING and a sub-query all producing a casting error.

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  • Google calendar query returns at most 25 entries

    - by Dean Hill
    I'm trying to delete all calendar entries from today forward. I run a query then call getEntries() on the query result. getEntries() always returns 25 entries (or less if there are fewer than 25 entries on the calendar). Why aren't all the entries returned? I'm expecting about 80 entries. As a test, I tried running the query, deleting the 25 entries returned, running the query again, deleting again, etc. This works, but there must be a better way. Below is the Java code that only runs the query once. CalendarQuery myQuery = new CalendarQuery(feedUrl); DateFormat dfGoogle = new SimpleDateFormat("yyyy-MM-dd'T00:00:00'"); Date dt = Calendar.getInstance().getTime(); myQuery.setMinimumStartTime(DateTime.parseDateTime(dfGoogle.format(dt))); // Make the end time far into the future so we delete everything myQuery.setMaximumStartTime(DateTime.parseDateTime("2099-12-31T23:59:59")); // Execute the query and get the response CalendarEventFeed resultFeed = service.query(myQuery, CalendarEventFeed.class); // !!! This returns 25 (or less if there are fewer than 25 entries on the calendar) !!! int test = resultFeed.getEntries().size(); // Delete all the entries returned by the query for (int j = 0; j < resultFeed.getEntries().size(); j++) { CalendarEventEntry entry = resultFeed.getEntries().get(j); entry.delete(); } PS: I've looked at the Data API Developer's Guide and the Google Data API Javadoc. These sites are okay, but not great. Does anyone know of additional Google API documentation?

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  • Error 1009 after gotoAndStop - stage instance never gets added

    - by ELambda
    I've been through the forums for hours (days?) searching on 1009 errors, but I remain stumped on this. It seems very mysterious and I would LOVE some help if you have any ideas. I have a single .swf that is 7 frames long - each frame represents a different "page" and you can switch pages through a menu widget in the top right corner. The menu widget calls gotoAndPlay( "frame" ). Everything works fine except when I switch from one particular frame to another. Then, during initialization of the new frame (setting some visible properties on various items, in actionscript), I get the dreaded 1009 error on a specific stage instance, a dynamic text instance i_word. Here's what I've tried so far: made sure the actionscript for the new frame starts with a stop() statement before starting initialization - no dice tried changing i_word into a movie_clip instead of dynamic text, made sure it was exported for actionscript - no difference. (I also have 2 other dynamic text instances on the same page that don't seem to cause a problem) added an ENTER_FRAME listener when the new frame is loaded, in case the problem was a timing issue. Put in a big if statement checking if i_word and other instances are not null before proceeding to initialization. It never enters the if, because i_word NEVER gets added. I added trace statements for all instances that are null, and it is the only one. If I remove all references to i_word in my actionscript, everything else is not null, and things go forward. The text for i_word even shows up on the screen in that case. tried renaming i_word - no dice tried deleting the layer i_word was on and adding a new layer - no dice It feels like there is a serious Gremlin in my flash file somewhere. Or maybe I'm missing something obvious. Let me know if you have any ideas...I'd be so grateful. Thank you! Elambda

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  • Difference between two PHP times as years, months and days for PHP version 5.2

    - by Dominor Novus
    Forward: I've scanned through the existing questions/answers on this matter. This is not a duplicitous question; I cannot find a working solution from the accepted answers. The main questions/answers I've reviewed can be found here: How to calculate the difference between two dates using PHP? What I need: A calucalation of the difference between two dates expressed as years, months and days that works with PHP version: 5.2. <?php $current_date = date('d-M-Y'); $future_date = '2012-11-01'; ?> What I've tried: Most answers I find online don't seem to exact in that they don't factor in leap years. This highly rated answer won't work because DateTime-diff() is php 5.3+. This accepted answer results in (i.e. the second block of code aimed at PHP 5.2) results in the following being parsed: Array ( [y] = 25 [m] = 11 [d] = 7 [h] = 3 [i] = 15 [s] = 19 [invert] = 0 [days] = 9473 ) Array ( [y] = 25 [m] = 11 [d] = 7 [h] = 3 [i] = 15 [s] = 19 [invert] = 1 [days] = 9473 ) I can't tell if I've incorrectly applied the code or it's simply a case of me not knowing how to manipulate the array.

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  • C# Sql Connection Best Practises 2013

    - by Pete Petersen
    With the new year approaching I'm drawing up a development plan for 2013. I won't bore you with the details but I started thinking about whether the way I do things is actually the 'correct' way. In particular how I'm interfacing with SQL. I create predominantly create WPF desktop applications and often some Silverlight Web Applications. All of my programs are very Data-Centric. When connecting to SQL from WPF I tend to use Stored Procedures stored on the server and fetch them using ADO.NET (e.g. SQLConnection(), .ExecuteQuery()). However with Silverlight I have a WCF service and use LINQ to SQL (and I'm using LINQ much more in WPF). My question is really is am I doing anything wrong in a sense that it's a little old fashioned? I've tried to look this up online but could find anything useful after about 2010 and of those half were 'LINQ is dead!' and the other 'Always use LINQ' Just want to make sure going forward I'm doing the right things the right way, or at least the advised way :). What principles are you using when connecting to SQL? Is it the same for WPF and Silverlight/WCF?

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  • How do I do a table join on two fields in my second table?

    - by Cannonade
    I have two tables: Messages - Amongst other things, has a to_id and a from_id field. People - Has a corresponding person_id I am trying to figure out how to do the following in a single linq query: Give me all messages that have been sent to and from person x (idself). I had a couple of cracks at this. Not quite right MsgPeople = (from p in db.people join m in db.messages on p.person_id equals m.from_id where (m.from_id == idself || m.to_id == idself) orderby p.name descending select p).Distinct(); This almost works, except I think it misses one case: "people who have never received a message, just sent one to me" How this works in my head So what I really need is something like: join m in db.messages on (p.people_id equals m.from_id or p.people_id equals m.to_id) Gets me a subset of the people I am after It seems you can't do that. I have tried a few other options, like doing two joins: MsgPeople = (from p in db.people join m in AllMessages on p.person_id equals m.from_id join m2 in AllMessages on p.person_id equals m2.to_id where (m2.from_id == idself || m.to_id == idself) orderby p.name descending select p).Distinct(); but this gives me a subset of the results I need, I guess something to do with the order the joins are resolved. My understanding of LINQ (and perhaps even database theory) is embarrassingly superficial and I look forward to having some light shed on my problem.

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  • ApplicationDispatcher exception

    - by JFB
    Whenever I try to redirect to a certain page using this dispatch method that is called from my doGet method, I get the following exception. I have no idea why! account controller servlet protected void dispatch(HttpServletRequest request, HttpServletResponse response, String page) throws javax.servlet.ServletException, java.io.IOException { RequestDispatcher dispatcher = getServletContext() .getRequestDispatcher(page); try { dispatcher.forward(request, response); } catch (java.lang.NullPointerException e) { System.out.println("NullPointerException: attribute expected in view"); } } Error msg java.lang.NullPointerException org.apache.jasper.JasperException: java.lang.NullPointerException org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:502) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:430) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) controller.AccountController.dispatch(AccountController.java:91) controller.AccountController.doExecute(AccountController.java:72) controller.AccountController.doGet(AccountController.java:34) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) java.lang.NullPointerException org.apache.jsp.content.edit_jsp._jspService(edit_jsp.java:109) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) controller.AccountController.dispatch(AccountController.java:91) controller.AccountController.doExecute(AccountController.java:72) controller.AccountController.doGet(AccountController.java:34) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

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  • Name lookup for names not dependent on template parameter in VC++2008 Express. Is it a bug?

    - by Maciej H
    While experimenting a bit with C++ templates I managed to produce this simple code, for which the output is different, than I expected according to my understanding of C++ rules. void bar(double d) { std::cout << "bar(double) function called" << std::endl; } template <typename T> void foo(T t) { bar(3); } void bar(int i) { std::cout << "bar(int) function called" << std::endl; } int main() { foo(3); return 0; } When I compile this code is VC++2008 Express function bar(int) gets called. That would be the behaviour I would expect if bar(3);in the template body was dependent on the template parameter. But it's not. The rule I found here says "The C++ standard prescribes that all names that are not dependent on template parameters are bound to their present definitions when parsing a template function or class". Am I wrong, that "present definition" of bar when parsing the template function foo is the definition of void bar(double d);? Why it's not the case if I am wrong. There are no forward declarations of bar in this compilation unit.

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  • mod_rewrite: no access to real files and directories

    - by tshabalala
    Hello. I use mod_rewrite/.htaccess for pretty URLs. I forward all the requests to my index.php, like this: RewriteRule ^/?([a-zA-Z0-9/-]+)/?$ /index.php [NC,L] The index.php then handles the requests. I'm also using this condition/rule to eliminate trailing slashes (or rather rewrite them to the URL without a trailing slash, with a 301 redirect; I'm doing this to avoid duplicate content and because I like no trailing slashes better): RewriteCond %{HTTP_HOST} !^\.localhost$ [NC] RewriteRule ^(.+)/$ http://%{HTTP_HOST}/$1 [R=301,L] This works well, except that I now get an infinite loop when trying to access a (real) directory (the rewrite rule removes the trailing slash, the server adds it again, ...). I solved this by setting the DirectorySlash directive to Off: DirectorySlash Off I don't know how good this solution is, I don't feel too confident about it tbh. Anyway, what I'd like to do is completely ignore "real" files and directories, since I don't need them and I only use pretty URLs with "virtual" files/directories anyway. This would allow me to avoid the DirectorySlash workaround/hack too. Is this possible? Thanks!

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  • Visual Studio 2010 compile error with std::string?

    - by AJG85
    So this is possibly the strangest thing I've seen recently and was curious how this could happen. The compiler gave me an error saying that std::string is undefined when used as a return type but not when used as a parameter in methods of a class! #pragma once #include <string> #include <vector> // forward declarations class CLocalReference; class CResultSetHandle; class MyClass { public: MyClass() {} ~MyClass {} void Retrieve(const CLocalReference& id, CResultSetHandle& rsh, std::string& item); // this is fine const std::string Retrieve(const CLocalReference& id, CResultSetHandle& rsh); // this fails with std::string is undefined?!?! }; Doing a Rebuild All it still happened I had to choose clean solution and then Rebuild All again after for the universe to realign. While it's resolved for the moment I'd still like to know what could have caused this because I'm at a loss as to why when there should be no conflicts especially when I always use fully qualified names for STL.

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  • Is std::move really needed on initialization list of constructor for heavy members passed by value?

    - by PiotrNycz
    Recently I read an example from cppreference.../vector/emplace_back: struct President { std::string name; std::string country; int year; President(std::string p_name, std::string p_country, int p_year) : name(std::move(p_name)), country(std::move(p_country)), year(p_year) { std::cout << "I am being constructed.\n"; } My question: is this std::move really needed? My point is that compiler sees that this p_name is not used in the body of constructor, so, maybe, there is some rule to use move semantics for it by default? That would be really annoying to add std::move on initialization list to every heavy member (like std::string, std::vector). Imagine hundreds of KLOC project written in C++03 - shall we add everywhere this std::move? This question: move-constructor-and-initialization-list answer says: As a golden rule, whenever you take something by rvalue reference, you need to use it inside std::move, and whenever you take something by universal reference (i.e. deduced templated type with &&), you need to use it inside std::forward But I am not sure: passing by value is rather not universal reference?

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  • Collision Detection (Ground & Slopes) in 2D Platform Game using Pygame Rects

    - by RedCap
    Hi, First off, I am not after any instructions on logic for collision detection; I get it. What I am trying to work out is the least complicated way to do this with Pygame using Sprites & Rects. I want to be able to check collisions for the Player against ground, walls & slopes. In theory it is quite straight forward, but I'm having difficulty because it seems like you cannot do this with one Rect. One Rect is simple enough to get you collisions in the X plane against walls. The same Rect could be used also be used in the Y plane against solids, but not with slopes - since with the collision routines in Pygame it checks the whole Rect (or mask), rather than perhaps just the bottom middle of the Rect. It seems in addition you need to have a number of "sprites" to check collisions with, that are 1x1 pixel in various places around the Player. What's the easiest way to do this, without having a bunch of 3, 4, or more separate "collision pixels" to check against slopes? Geoff

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  • Need help with Django tutorial

    - by Nai
    I'm doing the Django tutorial here: http://docs.djangoproject.com/en/1.2/intro/tutorial03/ My TEMPLATE_DIRS in the settings.py looks like this: TEMPLATE_DIRS = ( "/webapp2/templates/" "/webapp2/templates/polls" # Put strings here, like "/home/html/django_templates" or "C:/www/django/templates". # Always use forward slashes, even on Windows. # Don't forget to use absolute paths, not relative paths. ) My urls.py looks like this: from django.conf.urls.defaults import * from django.contrib import admin admin.autodiscover() urlpatterns = patterns('', (r'^polls/$', 'polls.views.index'), (r'^polls/(?P<poll_id>\d+)/$', 'polls.views.detail'), (r'^polls/(?P<poll_id>\d+)/results/$', 'polls.views.results'), (r'^polls/(?P<poll_id>\d+)/vote/$', 'polls.views.vote'), (r'^admin/', include(admin.site.urls)), ) My views.py looks like this: from django.template import Context, loader from polls.models import Poll from django.http import HttpResponse def index(request): latest_poll_list = Poll.objects.all().order_by('-pub_date')[:5] t = loader.get_template('c:/webapp2/templates/polls/index.html') c = Context({ 'latest_poll_list': latest_poll_list, }) return HttpResponse(t.render(c)) I think I am getting the path of my template wrong because when I simplify the views.py code to something like this, I am able to load the page. from django.http import HttpResponse def index(request): return HttpResponse("Hello, world. You're at the poll index.") My index template file is located at C:/webapp2/templates/polls/index.html. What am I doing wrong?

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  • Checking servlet session attribute value in jsp file

    - by Marta
    I have a no framework java application. It consists of jsp files for view and servlets for the business logic. I must set the user session is the servlet with a firstName parameter. In the jsp file, I need to check if my firstName parameter has a value or not. If the firstName parameter is set, I need to display some html in the jsp file. If it is not set, I need to display different html in the jsp file. Servlet.java: HttpSession session = request.getSession(); session.setAttribute("firstName", customer.getFristName()); String url = "/index.jsp"; RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url); dispatcher.forward(request, response); header.jsp: // Between the <p> tags bellow I need to put some HTML with the following rules // If firstName exist: Hello ${firstName} <a href="logout.jsp">Log out</a> // Else: <a href="login.jsp">Login</a> or <a href="register.jsp">Register</a> <p class="credentials" id="cr"></p> What would be the best way to do this? Any help is much appreciated! Thank you in advance. -Marta

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  • What are good examples of perfectly acceptable approaches to development that are NOT test driven development (TDD)?

    - by markbruns
    The TDD cycle is test, code, refactor, (repeat) and then ship. TDD implies development that is driven by testing, specifically that means understanding requirements and then writing tests first before developing or writing code. My natural inclination is a philosophical bias in favor of TDD; I would like to be convinced that there are other approaches that now work well or even better than TDD so I have asked this question. What are examples of perfectly acceptable approaches that NOT test driven development? I can think of plenty approaches that are not TDD but could be a lot more trouble than what they are worth ... it's not moral judgement, it's just that they are cost more than they are worth ... the following are simply examples of things that might be ok as learning exercises, but approaches I'd find to be NOT acceptable in serious production and NOT TDD might include: Inspecting quality into your product -- Focusing efforts on developing a proficiency in testing/QA can be problematic, especially if you don't work on the requirements and development side first ... symptom of this include bug triaging where the developers have so many different bugs to deal with it, it is necessary to employ a form of triage -- each development cycle gets worse and worse, programmers work more and more hours, sleep less and less, struggle to keep going in death march until they are consumed. Superstition ... believing in things that you don't understand -- this would involve borrowing code that you believe has been proven or tested from somewhere, e.g. legacy code, a magic code starter wizard or an open source project, and you go forward hacking up a storm of modifications, sliding FaceBook Connect into your the user interface, inventing some new magic features on the fly (e.g. a mashup using the Twitter API, GoogleMaps API and maybe Zappos API), showing off your cool new "product" to a few people and then writing up a simple "specification" and list of "test cases" and turning that over to Mechanical Turk for testing.

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  • Servlets: forwarding to a resource in a different webapp

    - by skaffman
    I'm trying to construct a java web app along modular principles, with some common resources (JSPs, mainly) in one WAR, and some custom resources in another. This means JSPs scattered across different WARs. Now JavaEE frowns upon this sort of shenanigans, and wants you to put everything in one place. My current workaround to this is to have an Eclipse-triggered Ant script which copies the content of one WAR into the other, but this is not a pleasant solution (it's fragile and too IDE-dependent). Ideally, what I'd like to be able to do is for a servlet to forward to a JSP located in a different WAR to one in which it is itself deployed. This would allow greater freedom in how I assemble my WARs. However, the RequestDispatcher does not seem to support such things. Another possibility is to use <c:import>, which does allow resources to be imported from a different WAR (with some caveats). This would probably allow me to have a "hook" JSP in one WAR, which then drags in the required JSP from another. This is a bit clunky, though, and the fact that <c:import> permits it shows that the underlying servlet API does also. But how do I access that functionality via the RequestDispatcher in a servlet?

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  • Nested bind expressions

    - by user328543
    This is a followup question to my previous question. #include <functional> int foo(void) {return 2;} class bar { public: int operator() (void) {return 3;}; int something(int a) {return a;}; }; template <class C> auto func(C&& c) -> decltype(c()) { return c(); } template <class C> int doit(C&& c) { return c();} template <class C> void func_wrapper(C&& c) { func( std::bind(doit<C>, std::forward<C>(c)) ); } int main(int argc, char* argv[]) { // call with a function pointer func(foo); func_wrapper(foo); // error // call with a member function bar b; func(b); func_wrapper(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); func_wrapper(std::bind(&bar::something, b, 42)); // error // call with a lambda expression func( [](void)->int {return 42;} ); func_wrapper( [](void)->int {return 42;} ); return 0; } I'm getting a compile errors deep in the C++ headers: functional:1137: error: invalid initialization of reference of type ‘int (&)()’ from expression of type ‘int (*)()’ functional:1137: error: conversion from ‘int’ to non-scalar type ‘std::_Bind(bar, int)’ requested func_wrapper(foo) is supposed to execute func(doit(foo)). In the real code it packages the function for a thread to execute. func would the function executed by the other thread, doit sits in between to check for unhandled exceptions and to clean up. But the additional bind in func_wrapper messes things up...

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  • Best loose way to get objects with common base class

    - by Michael Teper
    I struggled to come up with a good title for this question, so suggestions are welcome. Let's say we have an abstract base class ActionBase that looks something like this: public abstract class ActionBase { public abstract string Name { get; } public abstract string Description { get; } // rest of declaration follows } And we have a bunch of different actions defined, like a MoveFileAction, WriteToRegistryAction, etc. These actions get attached to Worker objects: public class Worker { private IList<ActionBase> _actions = new List<ActionBase>(); public IList<ActionBase> Actions { get { return _actions; } } // worker stuff ... } So far, pretty straight-forward. Now, I'd like to have a UI for setting up Workers, assigning Actions, setting properties, and so on. In this UI, I want to present a list of all available actions, along with their properties, and for that I'd want to first gather up all the names and descriptions of available actions (plus the type) into a collection of the following type of item: public class ActionDescriptor { public string Name { get; } public string Description { get; } poblic Type Type { get; } } Certainly, I can use reflection to do this, but is there a better way? Having Name and Description be instance properties of ActionBase (as opposed to statics on derived classes) smells a bit, but there isn't an abstract static in C#. Thank you!

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  • Java - Image encoding in XML

    - by Hoopla
    Hi everyone, I thought I would find a solution to this problem relatively easily, but here I am calling upon the help from ye gods to pull me out of this conundrum. So, I've got an image and I want to store it in an XML document using Java. I have previously achieved this in VisualBasic by saving the image to a stream, converting the stream to an array, and then VB's xml class was able to encode the array as a base64 string. But, after a couple of hours of scouring the net for an equivalent solution in Java, I've come back empty handed. The only success I have had has been by: import it.sauronsoftware.base64.*; import java.awt.image.BufferedImage; import org.w3c.dom.*; ... BufferedImage img; Element node; ... java.io.ByteArrayOutputStream os = new java.io.ByteArrayOutputStream(); ImageIO.write(img, "png", os); byte[] array = Base64.encode(os.toByteArray()); String ss = arrayToString(array, ","); node.setTextContent(ss); ... private static String arrayToString(byte[] a, String separator) { StringBuffer result = new StringBuffer(); if (a.length > 0) { result.append(a[0]); for (int i=1; i<a.length; i++) { result.append(separator); result.append(a[i]); } } return result.toString(); } Which is okay I guess, but reversing the process to get it back to an image when I load the XML file has proved impossible. If anyone has a better way to encode/decode an image in an XML file, please step forward, even if it's just a link to another thread that would be fine. Cheers in advance, Hoopla.

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