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  • Why does Microsoft advise against readonly fields with mutable values?

    - by Weeble
    In the Design Guidelines for Developing Class Libraries, Microsoft say: Do not assign instances of mutable types to read-only fields. The objects created using a mutable type can be modified after they are created. For example, arrays and most collections are mutable types while Int32, Uri, and String are immutable types. For fields that hold a mutable reference type, the read-only modifier prevents the field value from being overwritten but does not protect the mutable type from modification. This simply restates the behaviour of readonly without explaining why it's bad to use readonly. The implication appears to be that many people do not understand what "readonly" does and will wrongly expect readonly fields to be deeply immutable. In effect it advises using "readonly" as code documentation indicating deep immutability - despite the fact that the compiler has no way to enforce this - and disallows its use for its normal function: to ensure that the value of the field doesn't change after the object has been constructed. I feel uneasy with this recommendation to use "readonly" to indicate something other than its normal meaning understood by the compiler. I feel that it encourages people to misunderstand the meaning of "readonly", and furthermore to expect it to mean something that the author of the code might not intend. I feel that it precludes using it in places it could be useful - e.g. to show that some relationship between two mutable objects remains unchanged for the lifetime of one of those objects. The notion of assuming that readers do not understand the meaning of "readonly" also appears to be in contradiction to other advice from Microsoft, such as FxCop's "Do not initialize unnecessarily" rule, which assumes readers of your code to be experts in the language and should know that (for example) bool fields are automatically initialised to false, and stops you from providing the redundancy that shows "yes, this has been consciously set to false; I didn't just forget to initialize it". So, first and foremost, why do Microsoft advise against use of readonly for references to mutable types? I'd also be interested to know: Do you follow this Design Guideline in all your code? What do you expect when you see "readonly" in a piece of code you didn't write?

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  • C Nested Structure Pointer Problem

    - by Halo
    I have a shared structure, and inside it a request structure: struct shared_data { pthread_mutex_t th_mutex_queue; struct request_queue { int min; int max; char d_name[DIR_SIZE]; pid_t pid; int t_index; } request_queue[BUFSIZE]; int count; int data_buffer_allocation[BUFSIZE]; int data_buffers[BUFSIZE][100]; }; Then I prepare a request; struct shared_data *sdata_ptr; ... ... sdata_ptr->request_queue[index].pid = pid; strcpy(sdata_ptr->request_queue[index].d_name, dir_path_name); sdata_ptr->request_queue[index].min = min; sdata_ptr->request_queue[index].max = max; And the compiler warns me that I'm doing an incompatible implicit declaration in the strcpy function. I guess that's a problem with the pointers, but isn't what I wrote above supposed to be true?

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  • C++ Switch won't compile with externally defined variable used as case

    - by C Nielsen
    I'm writing C++ using the MinGW GNU compiler and the problem occurs when I try to use an externally defined integer variable as a case in a switch statement. I get the following compiler error: "case label does not reduce to an integer constant". Because I've defined the integer variable as extern I believe that it should compile, does anyone know what the problem may be? Below is an example: test.cpp #include <iostream> #include "x_def.h" int main() { std::cout << "Main Entered" << std::endl; switch(0) { case test_int: std::cout << "Case X" << std::endl; break; default: std::cout << "Case Default" << std::endl; break; } return 0; } x_def.h extern const int test_int; x_def.cpp const int test_int = 0; This code will compile correctly on Visual C++ 2008. Furthermore a Montanan friend of mine checked the ISO C++ standard and it appears that any const-integer expression should work. Is this possibly a compiler bug or have I missed something obvious? Here's my compiler version information: Reading specs from C:/MinGW/bin/../lib/gcc/mingw32/3.4.5/specs Configured with: ../gcc-3.4.5-20060117-3/configure --with-gcc --with-gnu-ld --with-gnu-as --host=mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable-languages=c,c++,f77,ada,objc,java --disable-win32-registry --disable-shared --enable-sjlj-exceptions --enable-libgcj --disable-java-awt --without-x --enable-java-gc=boehm --disable-libgcj-debug --enable-interpreter --enable-hash-synchronization --enable-libstdcxx-debug Thread model: win32 gcc version 3.4.5 (mingw-vista special r3)

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  • Recommend me an architecture for this Facebook application

    - by andybaird
    Firstly, this question is subjective. There is not a right answer for this question and it really depends on what works for you. I'm hoping to use this thread as a breeding ground for ideas. I hope this is acceptable in this medium. I'm working on building a Facebook app that will be replacing an already popular app that gets ~50k hits a day. The original app is using a very typical LAMP setup with help from some Zend libraries for database layer extraction. For the most part the app worked well, except to solve a lot of issues I ended up fragmenting tables to speed things up. As a result, I couldn't do a lot of things with the app that I wanted to (namely any processing using aggregate data that needed to be returned quickly) So I'm starting to design plans for the next version of this application, and I have a whole bunch of new and cool features that I know would choke my current setup. I'm looking for technological recommendations of data storage methods that scale well. The database does not necessarily need to be relational, simple key/value storage would suffice (although at present time I know little to nothing about KV stores) What's your recommendation? How would you tackle this? I'd like to take a completely free approach to this -- although I am most familiar and comfortable using PHP, I want to leave all technical options open.

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  • One big executable or many small DLL's?

    - by Patrick
    Over the years my application has grown from 1MB to 25MB and I expect it to grow further to 40, 50 MB. I don't use DLL's, but put everything in this one big executable. Having one big executable has certain advantages: Installing my application at the customer is really: copy and run. Upgrades can be easily zipped and sent to the customer There is no risk of having conflicting DLL's (where the customer has version X of the EXE, but version Y of the DLL) The big disadvantage of the big EXE is that linking times seem to grow exponentially. Additional problem is that a part of the code (let's say about 40%) is shared with another application. Again, the advantages are that: There is no risk on having a mix of incorrect DLL versions Every developer can make changes on the common code which speeds up developments. But again, this has a serious impact on compilation times (everyone compiles the common code again on his PC) and on linking times. The question http://stackoverflow.com/questions/2387908/grouping-dlls-for-use-in-executable mentions the possibility of mixing DLL's in one executable, but it looks like this still requires you to link all functions manually in your application (using LoadLibrary, GetProcAddress, ...). What is your opinion on executable sizes, the use of DLL's and the best 'balance' between easy deployment and easy/fast development?

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  • How to deploy a number of disparate project types?

    - by niteice
    This question is similar to http://stackoverflow.com/questions/1900269/whats-the-best-way-to-deploy-an-executable-process-on-a-web-server. The situation is this: I'm developing a product that needs to be deployed to a web server. It consists of 4 website projects, a background service, a couple of command-line tools, and two assemblies shared by all of these components. Now, I also happen to administer the server that this product will be deployed on. So I'm familiar with everything that may need to be done to perform an update: Copy website files Replace the service binary Install updated components in the GAC Configure IIS Update database schema After some research it seems that, to reduce deployment time and to be able to let the other sysadmins handle deployment, I want to deploy all of these as an MSI, except that I don't know a thing about installers. I know VS can generate web deployment projects, but where do I go from there? Being able to simply click Next a few times on an installer is my goal for deploying updates. It would also be nice to modularize it, so for example, I could distribute the four websites among multiple servers and have everything appear as individual components in the installer, and as one entity in Add/Remove Programs. Is all of this too much to ask in a single package?

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  • Need help with Layouts in Swing

    - by Malki
    Hi, I'm using Java Swing and I have the following problem: I have a class TnaiPanel that extends JPanel. In this class I am creating 3 components and then lay them out in a horizontal line using a BoxLayout. Also, I have a class TnaimDinamimPanel that also extends JPanel. This class contains multiple occurances of TnaiPanel, layed out vertically using a BoxLayout. Also, I have a class MainFrame that extends JFrame. This frame contains a menu-bar and one main panel. The main panel can change (when choosing a certain menu-item, I create a new panel and set it to show as the main panel of the frame). Now, for some reason I get "BoxLayout can't be shared" when I add the newly created TnaimDinamimPanel to the components of the frame. I don't mind using different layout objects. The result I want to get is a sort of "table" of components, where each TnaiPanel will have fixed component sizes and spacing, essentially serving the role os a "row" in the "table". Thanks, Malki.

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  • ASP.Net MVC: Showing the same data using different layouts...

    - by vdh_ant
    Hi guys I'm wanting to create a page that allows the users to select how they would like to view their data - i.e. summary (which supports grouping), grid (which supports grouping), table (which supports grouping), map, time line, xml, json etc. Now each layout would probably have different use a different view model, which inherit from a common base class/view model. The reason being that each layout needs the object structure that it deals with to be different (some need hierarchical others a flatter structure). Each layout would call the same repository method and each layout would support the same functionality, i.e. searching and filtering (hence these controls would be shared between layouts). The main exception to this would be sorting which only grid and table views would need to support. Now my question is given this what do people think is the best approach. Using DisplayFor to handle the rendering of the different types? Also how do I work this with the actions... I would imagine that I would use the one action, and pass in the layout types, but then how does this support the grouping required for the summary, grid and table views. Do i treat each grouping as just a layout type Also how would this work from a URL point of view - what do people think is the template to support this layout functionality Cheers Anthony

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  • How can I marshal JSON to/from a POJO for BlackBerry Java?

    - by sowbug
    I'm writing a RIM BlackBerry client app. BlackBerry uses a simplified version of Java (no generics, no annotations, limited collections support, etc.; roughly a Java 1.3 dialect). My client will be speaking JSON to a server. We have a bunch of JAXB-generated POJOs, but they're heavily annotated, and they use various classes that aren't available on this platform (ArrayList, BigDecimal, XMLGregorianCalendar). We also have the XSD used by the JAXB-XJC compiler to generate those source files. Being the lazy programmer that I am, I'd really rather not manually translate the existing source files to Java 1.3-compatible JSON-marshalling classes. I already tried JAXB 1.0.6 xjc. Unfortunately, it doesn't understand the XSD file well enough to emit proper classes. Do you know of a tool that will take JAXB 2.0 XSD files and emit Java 1.3 classes? And do you know of a JSON marshalling library that works with old Java? I think I am doomed because JSON arrived around 2006, and Java 5 was released in late 2004, meaning that people probably wouldn't be writing JSON-parsing code for old versions of Java. However, it seems that there must be good JSON libraries for J2ME, which is why I'm holding out hope.

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  • Incompatible types when assigning to type 'struct compartido'

    - by user1660559
    I have one problem with this code. I should create one structure and share it across 5 new process created from the father: #include <stdio.h> #include <stdlib.h> #include <sys/wait.h> #include <unistd.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> #include <sys/sem.h> #include <time.h> struct compartido { int pid1, pid2, pid3, pid4, pid5; int propietario; int contador; int pidpadre; }; struct compartido var; int main(int argc, char *argv[]) { key_t llave1,llavesem; int idmem,idsem; llave1=ftok("/tmp",'a'); idmem=shmget(llave1,sizeof(int),IPC_CREAT|0600); if (idmem==-1) { perror ("shmget"); return 1; } var=shmat(idmem,0,0); /*This line is giving the error*/ /*rest of the code*/ } The exact error is giving is: error: incompatible types when assigning to type 'struct compartido' from type 'void *' I need to put this structure in the shared variable to be able to see and modify all those data from the 6 process (5 children and the father). What I'm doing bad? Thanks in advance and best regards,

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  • volatile keyword seems to be useless?

    - by Finbarr
    import java.util.concurrent.CountDownLatch; import java.util.concurrent.atomic.AtomicInteger; public class Main implements Runnable { private final CountDownLatch cdl1 = new CountDownLatch(NUM_THREADS); private volatile int bar = 0; private AtomicInteger count = new AtomicInteger(0); private static final int NUM_THREADS = 25; public static void main(String[] args) { Main main = new Main(); for(int i = 0; i < NUM_THREADS; i++) new Thread(main).start(); } public void run() { int i = count.incrementAndGet(); cdl1.countDown(); try { cdl1.await(); } catch (InterruptedException e1) { e1.printStackTrace(); } bar = i; if(bar != i) System.out.println("Bar not equal to i"); else System.out.println("Bar equal to i"); } } Each Thread enters the run method and acquires a unique, thread confined, int variable i by getting a value from the AtomicInteger called count. Each Thread then awaits the CountDownLatch called cdl1 (when the last Thread reaches the latch, all Threads are released). When the latch is released each thread attempts to assign their confined i value to the shared, volatile, int called bar. I would expect every Thread except one to print out "Bar not equal to i", but every Thread prints "Bar equal to i". Eh, wtf does volatile actually do if not this?

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  • G++ Multi-platform memory leak detection tool

    - by indyK1ng
    Does anyone know where I can find a memory memory leak detection tool for C++ which can be either run in a command line or as an Eclipse plug-in in Windows and Linux. I would like it to be easy to use. Preferably one that doesn't overwrite new(), delete(), malloc() or free(). Something like GDB if its gonna be in the command line, but I don't remember that being used for detecting memory leaks. If there is a unit testing framework which does this automatically, that would be great. This question is similar to other questions (such as http://stackoverflow.com/questions/283726/memory-leak-detection-under-windows-for-gnu-c-c ) however I feel it is different because those ask for windows specific solutions or have solutions which I would rather avoid. I feel I am looking for something a bit more specific here. Suggestions don't have to fulfill all requirements, but as many as possible would be nice. Thanks. EDIT: Since this has come up, by "overwrite" I mean anything which requires me to #include a library or which otherwise changes how C++ compiles my code, if it does this at run time so that running the code in a different environment won't affect anything that would be great. Also, unfortunately, I don't have a Mac, so any suggestions for that are unhelpful, but thank you for trying. My desktop runs Windows (I have Linux installed but my dual monitors don't work with it) and I'd rather not run Linux in a VM, although that is certainly an option. My laptop runs Linux, so I can use that tool on there, although I would definitely prefer sticking to my desktop as the screen space is excellent for keeping all of the design documentation and requirements in view without having to move too much around on the desktop. NOTE: While I may try answers, I won't mark one as accepted until I have tried the suggestion and it is satisfactory. EDIT2: I'm not worried about the cross-platform compatibility of my code, it's a command line application using just the C++ libraries.

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  • Correct Delphi compiler switches to stop in the user's code, not my component's

    - by Jeremy Mullin
    I'm modifying our VCL components so the end user's application links to our dcu files, instead of building our source code each time. We have everything working, but I want the debugger to stop on the user's code when an exception is raised. At first it would stop in our dcu and open the CPU window. I was able to prevent that by removing debug info from the dcu files. But now it still doesn't stop in the users code (like DevExpress libraries and others do). The following screencast is a short example. The first time I cause an exception in the DevExpress code, and the debugger correctly stops in my button event. The second time I cause an exception in my components, but the debugger doesn't have my button event on the call stack, and doesn't show me where the problem was. Any ideas why? http://screencast.com/t/NjhlOTRk Currently building the DCU's with these options: -$W+ -$D- -h -w -q Update: The TDataSet methods in between my component and the button event seem to cause this behavior. If I instead call a direct method of my table, I get the expected behavior. I'm guessing there isn't anything I can do about this, but I'm still curious why it happens.

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  • Approach for fixing NoClassDefFoundError?

    - by DJC
    I'm seeing this question is getting asked a lot in many different contexts. Perhaps we can set some strategies for locating and fixing it? I'm noobish myself so all I can contribute are horror stories and questions, sorry... It seems this is thrown when a class is visible at compile time but not at run time... how can this happen? In my case I am developing an app that uses the Google APIs, in Eclipse, for the Android platform. I've configured the Project Properties / Java Build Path / Libraries to include the gdata .jars and all is well. When I execute in the emulator I get a force close and the logcat shows a NoClassDefFoundError on a simple new ContactsService("myApp"); I've also tried a new CalendarService("myApp") with the same results. Is it possible or desirable to statically bind at compile time to avoid the problem? How could dynamic binding of an add-on library work in the mobile environment anyway? Either it has to be bound into my .apk or else I need to "install" it? ... hmmm. Advice much appreciated.

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  • c++ Mixing printf with wprintf (or cout with wcout)

    - by Bo Jensen
    I know you should not mix printing with printf,cout and wprintf,wcout, but have a hard time finding a good answer why and if it is possible to get round it. The problem is I use a external library that prints with printf and my own uses wcout. If I do a simple example it works fine, but from my full application it simply does not print the printf statements. If this is really a limitation, then there would be many libraries out there which can not work together with wide printing applications. Any insight on this is more than welcome. Update : I boiled it down to : #include <stdio.h> #include <stdlib.h> #include <iostream> #include <readline/readline.h> #include <readline/history.h> int main() { char *buf; std::wcout << std::endl; /* ADDING THIS LINE MAKES PRINTF VANISH!!! */ rl_bind_key('\t',rl_abort);//disable auto-complete while((buf = readline("my-command : "))!=NULL) { if (strcmp(buf,"quit")==0) break; std::wcout<<buf<< std::endl; if (buf[0]!=0) add_history(buf); } free(buf); return 0; } So I guess it might be a flushing problem, but it still looks strange to me, I have to check up on it.

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  • Python virtualenv questions

    - by orokusaki
    I'm using VirtualEnv on Windows XP. I'm wondering if I have my brain wrapped around it correctly. I ran virtualenv ENV and it created C:\WINDOWS\system32\ENV. I then changed my PATH variable to include C:\WINDOWS\system32\ENV\Scripts instead of C:\Python27\Scripts. Then, I checked out Django into C:\WINDOWS\system32\ENV\Lib\site-packages\django-trunk, updated my PYTHON_PATH variable to point the new Django directory, and continued to easy_install other things (which of course go into my new C:\WINDOWS\system32\ENV\Lib\site-packages directory). I understand why I should use VirtualEnv so I can run multiple versions of Django, and other libraries on the same machine, but does this mean that to switch between environments I have to basically change my PATH and PYTHON_PATH variable? So, I go from developing one Django project which uses Django 1.2 in an environment called ENV and then change my PATH and such so that I can use an environment called ENV2 which has the dev version of Django? Is that basically it, or is there some better way to automatically do all this (I could update my path in Python code, but that would require me to write machine-specific code in my application)? Also, how does this process compare to using VirtualEnv on Linux (I'm quite the beginner at Linux).

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  • Valgrind 'noise', what does it mean?

    - by Chris Huang-Leaver
    When I used valgrind to help debug an app I was working on I notice a huge about of noise which seems to be complaining about standard libraries. As a test I did this; echo 'int main() {return 0;}' | gcc -x c -o test - Then I did this; valgrind ./test ==1096== Use of uninitialised value of size 8 ==1096== at 0x400A202: _dl_new_object (in /lib64/ld-2.10.1.so) ==1096== by 0x400607F: _dl_map_object_from_fd (in /lib64/ld-2.10.1.so) ==1096== by 0x4007A2C: _dl_map_object (in /lib64/ld-2.10.1.so) ==1096== by 0x400199A: map_doit (in /lib64/ld-2.10.1.so) ==1096== by 0x400D495: _dl_catch_error (in /lib64/ld-2.10.1.so) ==1096== by 0x400189E: do_preload (in /lib64/ld-2.10.1.so) ==1096== by 0x4003CCD: dl_main (in /lib64/ld-2.10.1.so) ==1096== by 0x401404B: _dl_sysdep_start (in /lib64/ld-2.10.1.so) ==1096== by 0x4001471: _dl_start (in /lib64/ld-2.10.1.so) ==1096== by 0x4000BA7: (within /lib64/ld-2.10.1.so) * large block of similar snipped * ==1096== Use of uninitialised value of size 8 ==1096== at 0x4F35FDD: (within /lib64/libc-2.10.1.so) ==1096== by 0x4F35B11: (within /lib64/libc-2.10.1.so) ==1096== by 0x4A1E61C: _vgnU_freeres (vg_preloaded.c:60) ==1096== by 0x4E5F2E4: __run_exit_handlers (in /lib64/libc-2.10.1.so) ==1096== by 0x4E5F354: exit (in /lib64/libc-2.10.1.so) ==1096== by 0x4E48A2C: (below main) (in /lib64/libc-2.10.1.so) ==1096== ==1096== ERROR SUMMARY: 3819 errors from 298 contexts (suppressed: 876 from 4) ==1096== malloc/free: in use at exit: 0 bytes in 0 blocks. ==1096== malloc/free: 0 allocs, 0 frees, 0 bytes allocated. ==1096== For counts of detected errors, rerun with: -v ==1096== Use --track-origins=yes to see where uninitialised values come from ==1096== All heap blocks were freed -- no leaks are possible. You can see the full result here: http://pastebin.com/gcTN8xGp I have two questions; firstly is there a way to suppress all the noise? --show-below-main is set to no by default, but there doesn't appear to be a --show-after-main equivalent.

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  • Using StructureMap to create classes by a name?

    - by Bevan
    How can I use StructureMap to resolve to an appropriate implementation of an interface based on a name stored in an attribute? In my project, I have many different kinds of widgets, each descending from IWidget, and each decorated with an attribute specifying the kind of associated element. To illustrate: [Configuration("header")] public class HeaderWidget : IWidget { } [Configuration("linegraph")] public class LineGraphWidget : IWidget { } When processing my (XML) configuration file, I want to obtain an instance of the appropriate concrete class based on the name of the element I'm processing. public IWidget CreateWidget(XElement definition) { var kind = definition.Name.LocalName; var widget = // What goes here? widget.Configure(definition); return widget; } Each definition should result in a different widget being created - I don't need or want the instances to be shared. In the past I've written plenty of code to do this kind of thing manually, including writing a custom "roll-your-own" IoC container for one project. However, one of my goals with this project is to become proficient with StructureMap instead of reinventing the wheel. I think I've already managed to set up automatic scanning of assemblies so that StructureMap knows about all my IWidget implementations: public class WidgetRegistration : Registry { public WidgetRegistration() { Scan( scanner => { scanner.AssembliesFromApplicationBaseDirectory(); scanner.AddAllTypesOf<IWidget>(); }); } } However, this isn't registering the names of my widgets with StructureMap. What do I need to add to make my scenario work? (While I am trying to use StructureMap in this project, an answer showing me how to solve this problem with a different DI/IoC tool would still be valuable.)

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  • jquery-ui autocomplete with ASP MVC suggestions not displaying

    - by adamnickerson
    I have been trying to get a simple example of the jquery-ui autocomplete to work. I have a controller setup to handle the query, and it returns the json that looks to be in order, but I am getting no suggestions showing up. Here are the js libraries I am including: <script type="text/javascript" language="javascript" src="/Scripts/jquery-1.4.1.js"></script> <script type="text/javascript" language="javascript" src="/Scripts/jquery-ui-1.8.1.custom.min.js"></script> <link href="/Content/jquery-ui-1.8.1.custom.css" rel="stylesheet" type="text/css" /> and here is the javascript and the form tags: <script type="text/javascript"> $(function () { $("#organization").autocomplete({ source: function (request, response) { $.ajax({ url: '/Organization/OrganizationLookup', dataType: "json", data: { limit: 12, q: request.term } }) }, minLength: 2 }); }); </script> <div class="ui-widget"> <label for="organization">Organization: </label> <input id="organization" /> </div> I get back a json response that looks reasonable from my controller: [{"id":"Sector A","value":"Sector A"},{"id":"Sector B","value":"Sector B"},{"id":"Sector C","value":"Sector C"}] id and value seem to be the default naming that autocomplete is looking for. But I get no joy at all. Any thoughts?

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  • iphone: cross platform references and referencing external framework resources

    - by dan
    hi there working on an iphone app and separate framework. the separate framework is for an API that i'm building for use in multiple future apps. this api now needs to reference resources (images). what i would like to do is keep the resources WITH the API framework as local set of resources. i followed the instructions from http://www.clintharris.net/2009/iphone-app-shared-libraries/ to setup my app's project to use the headers from the separate API framework. what i can't seem to figure out is how to automatically load the framework's resources into the app's xcode environment so they can be linked in at app compile time. sure, i can drag the resources across from the framework into the main app's set of resources. but that seems kinda ugly and another step that possibly can be automated (??) anyone know of a better way? it would be great if any changes from the framework would be automatically available in the main app (due to the project 'link-age'). thanks for any help/tips/suggestions...

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  • In Java it seems Public constructors are always a bad coding practice

    - by Adam Gent
    This maybe a controversial question and may not be suited for this forum (so I will not be insulted if you choose to close this question). It seems given the current capabilities of Java there is no reason to make constructors public ... ever. Friendly, private, protected are OK but public no. It seems that its almost always a better idea to provide a public static method for creating objects. Every Java Bean serialization technology (JAXB, Jackson, Spring etc...) can call a protected or private no-arg constructor. My questions are: I have never seen this practice decreed or written down anywhere? Maybe Bloch mentions it but I don't own is book. Is there a use case other than perhaps not being super DRY that I missed? EDIT: I explain why static methods are better. .1. For one you get better type inference. For example See Guava's http://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained .2. As a designer of the class you can later change what is returned with a static method. .3. Dealing with constructor inheritance is painful especially if you have to pre-calculate something.

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  • [F#] Parallelize code in nested loops

    - by Juliet
    You always hear that functional code is inherently easier to parallelize than non-functional code, so I decided to write a function which does the following: Given a input of strings, total up the number of unique characters for each string. So, given the input [ "aaaaa"; "bbb"; "ccccccc"; "abbbc" ], our method will returns a: 6; b: 6; c: 8. Here's what I've written: (* seq<#seq<char>> -> Map<char,int> *) let wordFrequency input = input |> Seq.fold (fun acc text -> (* This inner loop can be processed on its own thread *) text |> Seq.choose (fun char -> if Char.IsLetter char then Some(char) else None) |> Seq.fold (fun (acc : Map<_,_>) item -> match acc.TryFind(item) with | Some(count) -> acc.Add(item, count + 1) | None -> acc.Add(item, 1)) acc ) Map.empty This code is ideally parallelizable, because each string in input can be processed on its own thread. Its not as straightforward as it looks since the innerloop adds items to a Map shared between all of the inputs. I'd like the inner loop factored out into its own thread, and I don't want to use any mutable state. How would I re-write this function using an Async workflow?

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  • Atomically maintaining a counter using Sub-sonic ActiveRecord

    - by cantabilesoftware
    I'm trying to figure out the correct way to atomically increment a counter in one table and use that incremented value as an pseudo display-only ID for a record in another. What I have is a companies table and a jobs table. I want each company to have it's own set of job_numbers. I do have an auto increment job_id, but those numbers are shared across all companies. ie: the job numbers should generally increment without gaps for each company. ie: companies(company_id, next_job_number) jobs(company_id, job_id, job_number) Currently I'm doing this (as a method on the partial job class): public void SaveJob() { using (var scope = new System.Transactions.TransactionScope()) { if (job_id == 0) { _db.Update<company>() .SetExpression("next_job_number").EqualTo("next_job_number+1") .Where<company>(x => x.company_id == company_id) .Execute(); company c = _db.companies.SingleOrDefault(x => x.company_id == company_id); job_number = c.next_job_number; } // Save the job this.Save(); scope.Complete(); } } It seems to work, but I'm not sure if there are pitfalls here? It just feels wrong, but I'm not sure how else to do it. Any advice appreciated.

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  • How to display a generic error page in Asp.Net MVC 2

    - by Picflight
    I have the following in my base controller: protected override void OnException(ExceptionContext filterContext) { if (filterContext == null) { throw new ArgumentNullException("filterContext"); } // If custom errors are disabled, we need to let the normal ASP.NET exception handler // execute so that the user can see useful debugging information. if (filterContext.ExceptionHandled || !filterContext.HttpContext.IsCustomErrorEnabled) { return; } Exception exception = filterContext.Exception; // If this is not an HTTP 500 (for example, if somebody throws an HTTP 404 from an action method), // ignore it. if (new HttpException(null, exception).GetHttpCode() != 500) { return; } // TODO: What is the namespace for ExceptionType? //if (!ExceptionType.IsInstanceOfType(exception)) //{ // return; //} // Send Email MailException(exception); // TODO: What does this line do? base.OnException(filterContext); filterContext.Result = new ViewResult { ViewName = "Error" }; filterContext.ExceptionHandled = true; filterContext.HttpContext.Response.Clear(); filterContext.HttpContext.Response.StatusCode = 500; } In my Shared folder, I have an Error.aspx View. Web.config <customErrors mode="On" /> I am still seeing the yellow screen when an exception occurs. What am I doing incorrectly?

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  • Why is PHP5 SQLite PDO silently failing on DB connection?

    - by danieltalsky
    I have no idea why my code is failing silently. PDO and PDO SQLite are confirmed loaded. Errors are turned on and OTHER errors display. The SQLite file exists. Perms are set correctly. If I change the filename, PHP actually DOES create the file but still fails silently. No output or commands are excecuted after the "$dbh = new PDO($db_conn);" command. I'm not sure what else I can possibly do to troubleshoot. What else... this is on Modwest shared hosting. ABOUT TO RUN <?php // Destination $db_name = '/confirmed/valid/path/DBName.db3'; $db_conn = 'sqlite:' . $db_name; try { var_dump($db_conn); $dbh = new PDO($db_conn); $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); } catch (Exception $e) { exit("Failed to open database: {$e->getMessage()} \n" ); } ?> THIS NEVER OUTPUTS! sdf

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