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• Why is there "data" and "newtype" in Haskell?

  - by martingw

  To me it seems that a newtype definition is just a data definition that obeys some restrictions (only one constructor and such), and that due to these restrictions the runtime system can handle newtypes more efficiently. Ok, and the handling of pattern matching for undefined values is slightly different. But suppose Haskell would only knew data definitions, no newtypes: Couldn't the compiler find out for himself whether a given data definition obeys these restrictions, and automatically treat it more efficiently? I'm sure I'm missing out on something, these Haskell designers are so clever, there must be some deeper reason for this...

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• What is a good solution to link different tables in Hibernate based on some field value?

  - by serg555

  I have article table and several user tables a_user, b_user, ... with exactly the same structure (but different data). I can't change anything in *_user tables except their table name prefix but can change everything else (user tables contain only user information, there is nothing about article or user_type in them). I need to link article to a user (many-to-one), but user table name is defined by user_type field. For example Article table record: ... user_id="5" user_type="a" means that it is linked to a user with id=5 from a_user table (id 5 is not unique in users scope, each user table can have its id 5). Any suggestions how to handle this situation? How can I map this relation in Hibernate (xml mapping, no annotations) so it will automatically pick up correct user for an article during select/update? How should I map user tables (one or multiple classes?)? I would need to run some queries like this: from Article a where a.userType=:type and a.user.name=:name Thanks.

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• bash copy with variable

  - by zaf

  I'm trying to copy files to the current directory using a bash script. In order to handle paths that need escaping a variable is used that is escaped and then supplied to the cp command. The cp command is complaining with: usage: cp [-R [-H | -L | -P]] [-fi | -n] [-apvX] source_file target_file cp [-R [-H | -L | -P]] [-fi | -n] [-apvX] source_file ... target_directory I know what that means but I cannot understand why that happens. Here is the code: z="/a/b/c d e f.txt" y=`printf %q "$z"` cp $y x.txt # not working as expected echo cp $y x.txt # output is "cp /a/b/c\ d\ e\ f.txt x.txt"

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• References/walkthroughs for maintaining database schemas with Visual Studio 2010?

  - by user206356

  I have Visual Studio 2010 Beta 2 and SQL Server 2008 installed. I'm working with a populated database and want to modify various column types. SQL Server Management Studio requires me to drop tables to do this, and get pretty finicky given my moderate level of knowledge of SQL Server. However, I heard the new database project type supports changing the database schema to the desired format and it will handle creating and running all the scripts to implement the changes. I've created a VS2010 database project using the existing database as the source, but so far haven't had much luck figuring out the appropriate method to make the changes without getting an error. As a result, I'm looking for any reference info I can find on using VS2010's capabilities in this area. Any suggestions?

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• Minimizing calls to database in rails

  - by ming yeow

  Hi guys, i am familiar with memcached and eager loading, but neither seems to solve the problem i am facing. My main performance lag comes from hundreds of data retrieval calls from the database. The tricky thing is that I do not know which set of users i need to retrieve until i have several steps of computation. I can refactor my code, but i was wondering how you experts handle this situation? I think it should be a fairly common situation def newsfeed - find out which users i need - retrieve those users via DB - find out which events happened for these users - for each of those events - retrieve new set of users - find out which groups are relevant - for each of those groups - retrieve new set of users - etc, etc end

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• 2D Game: Fast(est) way to find x closest entities for another entity - huge amount of entities, high

  - by Pygmy

  I'm working on a 2D game that has a huge amount of dynamic entities. For fun's sake, let's call them soldiers, and let's say there are 50000 of them (which I just randomly thought up, it might be much more or much less :)). All these soldiers are moving every frame according to rules - think boids / flocking / steering behaviour. For each soldier, to update it's movement I need the X soldiers that are closest to the one I'm processing. What would be the best spatial hierarchy to store them to facilitate calculations like this without too much overhead ? (All entities are updated/moved every frame, so it has to handle dynamic entities very well)

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• Error handling with Python + Pylons

  - by ensnare

  What is the proper way to handle errors with Python + Pylons? Say a user sets a password via a form that, when passed to a model class via the controller, throws an error because it's too short. How should that error be handled so that an error message gets displayed on the web page rather than the entire script terminating to an error page? Should there be any error handling in the controller itself? I hope I am explaining myself clearly. Thank you.

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• The best approach to customize Bootstrap Less files and keep it easy to be updated to future versions

  - by user322896

  I'm wondering what the best way would be to customize the less files in Bootstrap and, at the mean time, keep it easy to be updated to future Bootstrap versions. It's straightforward to just modify the less files, but the problem is that when the next version of Bootstrap comes out, it might be painful to upgrade (because all the changes are already deeply mixed with the original sources.) Another approach would be similar to the open closed principle, that is, keeping the original less files unchanged, and adding my customized less files to overwrite the CSS rules I need. When Bootstrap gets updated, (hopefully) I can simply replace the less files and everything would work magically. However, regardless of the correctness of my assumption, the same CSS rules would be scattered in even more places and hard to manage. Also, the more we overwrite the CSS (not for compatibility or other purposes), the more bandwidth we waste. I know this highly depends on how the author of Bootstrap would handle the structure of the framework or even the naming of CSS rules, but I'd still like to hear everybody's opinions. Thanks.

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• When is it a good idea to use the CSS display property?

  - by allyourcode

  I think I first learned of this property when I thought "I should put this list of items in a ul, but I want it to be laid out horizontally. I wonder if I can do that with CSS?" When I googled this, I found a couple of sites suggesting that I create a CSS rule that would change the value of the display property of the li elements to inline. I've also seen the suggestion that a div (or other block element) be given display: table-cell in order to force the vertical align property to work. These techniques seem kind of hacky. Does that make sense? This might not be a good analogy, but it seems like trying to ride a car as if it were a motorcycle. Yeah, I could replace the steering wheel with handle bars, wear a helmet, and remove all the passenger seating, but how the heck is a car going to drive on two wheels??

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• SqlCeCommand ExecuteNonQuery performance issue

  - by Michael

  I've been asked to resolve an issue with a .Net/SqlServerCe application. Specifically, after repeated inserts against the db, performance becomes increasingly degraded. In one instance at ~200 rows, in another at ~1000 rows. In the latter case the code being used looks like this: Dim cm1 As System.Data.SqlServerCe.SqlCeCommand = cn1.CreateCommand cm1.CommandText = "INSERT INTO Table1 Values(?,?,?,?,?,?,?,?,?,?,?,?,?)" For j = 0 To ds.Tables(0).Rows.Count - 1 'this is 3110 For i = 0 To 12 cm1.Parameters(tbl(i, 0)).Value = Vals(j,i) 'values taken from a different db Next cm1.ExecuteNonQuery() Next The specifics aren't super important (like what 'tbl' is, etc) but rather whether or not this code should be expected to handle this number of inserts, or if the crawl I'm witnessing is to be expected.

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• Correct Exceptions in C++

  - by Dr.Ackula

  I am just learning how to handle errors in my C++ code. I wrote this example that looks for a text file called some file, and if its not found will throw an exception. #include <iostream> #include <fstream> using namespace std; int main() { int array[90]; try { ifstream file; file.open("somefile.txt"); if(!file.good()) throw 56; } catch(int e) { cout<<"Error number "<<e<<endl; } return 0; } Now I have two questions. First I would like to know if I am using Exceptions correctly. Second, (assuming the first is true) what is the benefit to using them vs an If else statement?

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• C#, Manage concurrency in database access

  - by Goul

  Hi there, I have written a while ago an application used by multiple users to handle trades creation. I haven't done development for some time now and can't remember how I managed the concurrency between the users and so would have liked your advices in term of design. The application was as follow: - One heavy client per user - A single database - Access to the database for each user to insert/update/delete trades - A grid in the application reflecting the trades table. That grid being updated each time someone changes a deal. My questions: 1- Do you confirm I shouldn't care about the connection to the database for each application. Considering that there is a singleton in each, I would expect on connexion per client with no issue. 2- How preventing the concurrency of the accesses? I guess I should lock when modifying the data, however don't remember how to. 3- How to have the grid automatically updated whenever the database is (by another user for example)? Thank you in advance for your help!

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• How to create a Mutex with security attribute to share resource from different application?

  - by Antony Tess

  How to create a Mutex with security attribute rigth to share resource from different application? In according with Microsoft SDK documentation the CreateMutex API accept as first parameter a SECURITY_ATTRIBUTES pointer. HANDLE WINAPI CreateMutex( __in LPSECURITY_ATTRIBUTES lpMutexAttributes, __in BOOL bInitialOwner, __in LPCTSTR lpName ); I want to create the rigth security attribute so only my application group can open the MUTEX and access to a specific resource (a file) where my application gruop read/write data operation. The target opertaing system are XP, Vista and Seven. The feature must working in both, administrator/standard user, login shenario.

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• problem with the deletion of uploaded images

  - by tibin

  i got this error when i tried to delete an image which i have uploaded "Forbidden You don't have permission to access /act-photo-delete.php on this server. Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request. Apache/2.2.11 (Unix) mod_ssl/2.2.11 OpenSSL/0.9.8i DAV/2 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 Server at www.friendsjoint.com Port 80 " what will be the reason for this. i tried changing the chmods for the files. but nothing worked. is any one have an idea??? please help me....

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• How to store coordinates in a database

  - by Tim

  Hello all! I have a Flex GUI where I have to place quadrate elements. The position of these elements need to be stored into a database. So I can create two integer fields in the db table x and y. Also I need an angle, because the user can rotate these elements, so I can also make a int (int is okay, I do not need a double value therefore). As a ORM, I use Hibernate. But the question is, if creating three integer fields is the best way to handle this. Perhaps someone can tell me if this will be okay or if there are better ways? Thanks a lot in advance & Best Regards.

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• How do I identify where the POST data sent to a PHP script came from?

  - by Mike Turley

  I have a ton of data collection forms on my website, and I wrote a PHP script to handle all the data. All the forms have that one script as their action, and POST as the method. The handler emails a copy of the data to me, and I'd like for the emails I get to contain the URL of the form where they originated. Is there any way in PHP to get the url of the form which was submitted to the script? Or do I have to add an extra hidden field in every form with its URL?

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• Post data with jQuery to ASP.net, am I doing this secure enough?

  - by Wim Haanstra

  For a website I am building, I am using jQuery to post data to Generic Handlers I created for this purpose. Because you need to be logged in, to do most post actions (like 'rate a picture'), I am currently using the following technique: User visits page Page determines if user is logged in On Page_Load the page fills a hidden field with an encrypted string, which contains several needed variables, like User ID, Picture ID (of the picture they are currently viewing), the DateTime when the page was rendered. When the user clicks a "I like this picture"-button, I do a $.ajax post to my Generic Handler, with the encrypted string and the value whether or not they liked the picture. The Generic Handler decrypts the supplied encrypted string and takes a look at the DateTime to determine if it was not too long ago When everything works out, the vote is submitted to the database. In my understanding this is a pretty secure way to handle a situation like this. But maybe I am missing a very important point here. Any advice would be very welcome.

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• Idea for doing almost same work in both catch & finally(C#3.0)

  - by Newbie

  I have a requirement. I am processing some files and after the processing are done I am archiving those files into an archive folder with timestamp appended. The file archiving and putting time stamp portion I am doing in the Finally block. Now a new requirement has come where I need to mail if something wrong goes in the original files and then I need to archive the same. Now this piece of code I need to handle in the catch block. But if I write the code entirely in the catch block, then it will fire only if there is an exception; otherwise not. So basically I am writing the same pice of code in both the catch and finally block. What is the standard and recommended approach you people think will be better in this case? I am using C#3.0 Thanks.

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• python array.array with strings as data type

  - by Gladius

  Is there an object that acts like array.array, yet can handle strings (or character arrays) as its data type? It should be able to convert the string array to binary and back again, preferably with null terminated strings, however fixed length strings would be acceptable. >>> my_array = stringarray(['foo', 'bar']) >>> my_array.tostring() 'foo\0bar\0' >>> re_read = stringarray('foo\0bar\0') >>> re_read[:] ['foo', 'bar'] I will be using it with arrays that contain a couple million strings.

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• what's the right way to do polymorphism with protocol buffers?

  - by user364003

  I'm trying to long-term serialize a bunch of objects related by a strong class hierarchy in java, and I'd like to use protocol buffers to do it due to their simplicity, performance, and ease of upgrade. However, they don't provide much support for polymorphism. Right now, the way I'm handling it is by having a "one message to rule them all" solution that has a required string uri field that allows me to instantiate the correct type via reflection, then a bunch of optional fields for all the other possible classes I could serialize, only one of which will be used (based on the value of the uri field). Is there a better way to handle polymorphism, or is this as good as I'm going to get?

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• How to identify deadlock conditions in a third-party application?

  - by Imhotep is Invisible

  I am using a third-party application to handle batch CD audio extraction via multiple FireWire attached devices, but the application frequently (though non-deterministically) hangs during the extraction. I suspect that the multithreaded application is deadlocking over some shared resource. The developer, however, suspects the problem lies elsewhere but is not addressing the problem at this time. I would like to be able to do some legwork on my end to a) prove the condition exists and b) ideally point him in the right direction. The problems: while I used to be a programmer, it's been awhile and I need to shake off the dust (last work I did was back in '99 and it was under Solaris, while the application runs under XP). Rather than there being a dearth of information online, there's almost too much to digest. Are there any suggested guides or tutorials that might help me get back up to speed sufficient enough to help identify and/or diagnose the deadlock, or are there tools or approaches that I should study up on to aid me in my task? Many thanks for all suggestions!

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• Friendness and derived class

  - by ereOn

  Hi, Let's say I have the following class hierarchy: class Base { protected: virtual void foo() = 0; friend class Other; }; class Derived : public Base { protected: void foo() { /* Some implementation */ }; }; class Other { public: void bar() { Derived* a = new Derived(); a->foo(); // Compiler error: foo() is protected within this context }; }; I guess I could change it too a->Base::foo() but since foo() is pure virtual in the Base class, the call will result in calling Derived::foo() anyway. However, the compiler seems to refuse a->foo(). I guess it is logical, but I can't really understand why. Am I missing something ? Can't (shouldn't) it handle this special case ? Thank you.

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• What would be the best approach for this?

  - by chobo

  I have a site which has an area that requires authentication. Right now I use the roles attribute on all the controllers in that area, and I run a query to retrieve that users ID, and all their settings. It seems like a code or design smell to me that I am retrieving the userid and settings each time a controller in that area loads up? I'm not sure if I should be using sessions, or if ASP.Net MVC 2.0 provides some unique way to handle this. Another concern is security. Overall, I don't really know which way to turn. Design wise I would like the userId and settings retrieved only once when the user logs into the area. Right now I grab the userId each time a controller loads up, and then if required, I query the database for their settings each time as well.

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• Is there any memory restrictions on an ASP.Net application? HttpHandler?

  - by tpower

  I have an ASP.Net MVC application that allows users to upload images. When I try to upload a really large file (400MB) I get an error. I assumed that my image processing code (home brew) was very inefficient, so I decided I would try using a third party library to handle the image processing parts. Because I'm using TDD, I wanted to first write a test that fails. But when I test the controller action with the same large file it is able to do all the image processing without any trouble. The error I get is "Out of memory". I'm sure my code is probably using a lot more memory than it needs to but I just want to know why my test passes. The other difference is that I'm using SWFUpload which is not used with the test. Could this be the cause?

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• PHP: form input field names containing square brackets like field[index]

  - by gidireich

  Hi, I've seen lot of code that handle forms, which creates input fields with names containing square brackets. I understand that this is being somehow converted to PHP arrays when a PHP script examines the $_POST variable. My questions about this: What is the mechanism behind? At which point this names that merely contain brackets are converted to arrays? Is this a feature of the HTPP protocol? Of web servers? Of the PHP language? Continuing the previous question, is this a commonly used hack or a normal programming tool? What are (all) the rules of using brackets in input field names? Can multidimensional arrays be created this way? Thanks, Gidi

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