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• algorithm - How to sort a 0/1 array with 2n/3 comparisons?

  - by Jackson Tale

  In Algorithm Design Manual, there is such an excise 4-26 Consider the problem of sorting a sequence of n 0’s and 1’s using comparisons. For each comparison of two values x and y, the algorithm learns which of x < y, x = y, or x y holds. (a) Give an algorithm to sort in n - 1 comparisons in the worst case. Show that your algorithm is optimal. (b) Give an algorithm to sort in 2n/3 comparisons in the average case (assuming each of the n inputs is 0 or 1 with equal probability). Show that your algorithm is optimal. For (a), I think it is fairly easy. I can choose a[n-1] as pivot, then do something like in quicksort partition, scan 0 to n - 2, find the middle point where left side is all 0 and right side is all 1, this take n - 1 comparisons. But for (b), I can't get a clue. It says "each of the n inputs is 0 or 1 with equal probability", so I guess I can assume the numbers of 0 and 1 equal? But how can I get a result which is related to 1/3? divide the whole array into 3 groups? Thanks

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• can I add properties to a typo3 extbase domain model object?

  - by The Newbie Qs

  I want to store a username in a coupon object, each coupon object already has the uid of the user who created it. I can loop over the coupon objects and read the associated usernames from fe_users but how then will I save those usernames into the coupons so when they are passed to the template the usernames can be read like so coupon.username, or in some other easy way so each username will appear on the page with the right coupon as they are all printed out in a table? If I was doing basic php instead of typo3 i would just define a query but what is the typo3 v4.5 way? My code so far - which dies on the line where I try to assign the new property --creatorname -- to the $coup object. public function listAction() { $coupons = $this->couponRepository->findAll(); // @var Tx_Extbase_Domain_Repository_FrontendUserRepository $userRepository */ $userRepository = $this->objectManager->get("Tx_Extbase_Domain_Repository_FrontendUserRepository"); foreach ($coupons as $coup) { echo '<br />test '.$coup->getCreator(); echo '<br />count = '.$userRepository->countAll().'<br />'; $newObject = $userRepository->findByUid( intval($coup->getCreator())); //var_dump($newObject); var_dump($coup); echo '<br />getUsername '.$newObject->getUsername() ; $coup['creatorname'] = $newObject->getUsername(); echo '<br />creatorname '.$coup['creatorname'] ; } $this->view->assign('coupons', $coupons); }

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• Customizing the Stars Image for Ajaxful_Rating RoR plugin

  - by Kevin

  I'm trying to come up with my own star image that's slightly smaller and different style than the one provided in the gem/plugin, but Ajaxful_rating doesn't have an easy way to do this. Here's what I've figured out so far: The stars.png in the public folder is three 25x25 pixel tiles stacked vertically, ordered empty star, normal star, and hover star. I'm assuming as long as you keep the above constraints, you should be fine without modifying any other files. But what if you want to change the image size of the stars to larger or smaller? I've found where you can change the height in the stylesheets/ajaxful_rating.css .ajaxful-rating{ position: relative; /*width: 125px; this is setted dynamically */ height: 25px; overflow: hidden; list-style: none; margin: 0; padding: 0; background-position: left top; } .ajaxful-rating li{ display: inline; } .ajaxful-rating a, .ajaxful-rating span, .ajaxful-rating .show-value{ position: absolute; top: 0; left: 0; text-indent: -1000em; height: 25px; line-height: 25px; outline: none; overflow: hidden; border: none; } You just need to change every place that says "25px" above to whatever height your new star image is. This works fine but doesn't display the horizontal part correctly. Anyone know where I would look to set the horizontal part as well? (I'm assuming it's in an .rb file somewhere based upon how many stars you specified in your ajaxful_rating setup)

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• Creating many polygons with OpenGL is slow?

  - by user146780

  I want to draw many polygons to the screen but i'm quickly noticing that it slows down quickly. As a test I did this: for(int i = 0; i < 50; ++i) { glBegin( GL_POLYGON); glColor3f( 0.0f, 1, 0.0f ); glVertex2f( 500.0 + frameGL.GetCameraX(), 0.0f + frameGL.GetCameraY()); glColor3f( 0.0f, 1.0f, 0.0f ); glVertex2f( 900.0 + frameGL.GetCameraX(), 0.0f + frameGL.GetCameraY()); glColor3f( 0.0f, 0.0f, 0.5 ); glVertex2f(900.0 + frameGL.GetCameraX(), 500.0f + frameGL.GetCameraY() + (150)); glColor3f( 0.0f, 1.0f, 0.0f ); glVertex2f( 500 + frameGL.GetCameraX(), 500.0f + frameGL.GetCameraY()); glColor3f( 1.0f, 1.0f, 0.0f ); glVertex2f( 300 + frameGL.GetCameraX(), 200.0f + frameGL.GetCameraY()); glEnd(); } This is only 50 polygons and already it's gtting slow. I can't upload them directly to the card because my program will allow the user to reshape the verticies. My question is, how can I speed this up. I'm not using depth. I also know it's not my GetCamera() functions because if I create 500,000 polygons spread apart t's fine, it just has trouble showing them in the view. If a graphics card can support 500,000,000 on screen polygons per second, this should be easy right? Thanks

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• Where to give feedback on a new Feature is SO ?

  - by justjoe

  After using SO, for sometimes, i realize i got some problems. zen masters fighting each other on one of my question. Every side have their own arguments and Everybody seem right. Frankly, this make me confuse : How can i choose somebody's answer where personally i don't know the right answer. So, i would like to propose a feature 'i choose this because' for a user who asked. So at least he/she explain why he choose the particular answer. Maybe it's silly, but as somebody who getting helps from other's answer, i would like to know everybody get what they deserve. Usually in this kind of situation, i just upvote every good answer and check the one i think the right one. Second feature : every hot question always got plenty answer and comment. And if among person who answer it, start to debate then it will become a little bit hectic. Right now a page only have ability to sort answer based on oldest, newest votest. So, is it possible to make a new sort based on timeline what make comment and answer collide. I believe it will be more easy to read. this feature can only see by the person who create the question, or also for public.

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• Can't understand sessions in Rails

  - by ciss

  Hello everyone. Please don't bit my for my misunderstanding. The sessions are very new for me, and i have some problems. Okay i read many information about sessions and especially rails session. But this don't give me right imagine about sessions. Did i understand right, when users send request to server (get) - Server create a new session (and store this some file in hard drive with session id), session id - is a random generated num? so, server create a new session (and store session on drive) after this server send back answer to client and set session_id in cookies? Ok, i debug some params and see some results: debug(session): {:_csrf_token=>"jeONIfNxFmnpDn/xt6I0icNK1m3EB3CzT9KMntNk7KU=", :session_id=>"06c5628155efaa6446582c491499af6d", "flash"=>{}} debug(cookies): {"remember_user_token"=>"1::3GFRFyXb83lffzwPDPQd", "_blog_session"=>"BAh7CDoQX2NzcmZfdG9rZW4iMWplT05JZk54Rm1ucERuL3h0NkkwaWNOSzFtM0VCM0N6VDlLTW50Tms3S1U9Og9zZXNzaW9uX2lkIiUwNmM1NjI4MTU1ZWZhYTY0NDY1ODJjNDkxNDk5YWY2ZCIKZmxhc2hJQzonQWN0aW9uQ29udHJvbGxlcjo6Rmxhc2g6OkZsYXNoSGFzaHsABjoKQHVzZWR7AA==--348c88b594e98f4bf6389d94383134fbe9b03095"} Okay, i know, what _csrf_token helps to prevent csrf. session_id - is id of the session which stored on hard drive (by default) but what is _blog_session in cookies? also, remeber_user_token containes my id (1::*) and what about second part, what is it? Sorry for this stupid questions, i know what i can easy use any nice auth-plugins (authlogic/clearance/devise), but i want to fully understand sessions. Thank you. (also sorry for my english, this is not my native language)

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• Iterative printing over two data types in Python

  - by old Ixfoxleigh

  I often browse freely-available art on the web. Actually, I can't think of a better use for the internet than to turn it into a gigantic art gallery. When I encounter a set of pieces I quite like, I download them all to my hard drive. wget makes that easy, especially in combination with Python's print function, and I use this all the time to make a list of URLs that I then wget. Say I need to download a list of jpegs that run from art0 to art100 in the directory 'art,' I just tell python for i in range(0,101): print "http://somegallery/somedirectory/art", i So, this is probably a fairly simple operation in Python, and after a find-and-replace to remove whitespace, it's just a matter of using wget -i, but in days before I knew any Python I'd slavishly right-click and save. Now I've got a bunch of files from Fredericks & Freiser gallery in New York that all go a(1-14), b(1-14), c(1-14), etc., up to the letter g. I could do that in 7 goes, and it would take me less time than it took to write this SO question. That said, I want to deepen my knowledge of Python. So, given the letters a-g, how do I print a mapping of each letter to the integers 1-14?

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• Optimally place a pie slice in a rectangle.

  - by Lisa

  Given a rectangle (w, h) and a pie slice with start angle and end angle, how can I place the slice optimally in the rectangle so that it fills the room best (from an optical point of view, not mathematically speaking)? I'm currently placing the pie slice's center in the center of the rectangle and use the half of the smaller of both rectangle sides as the radius. This leaves plenty of room for certain configurations. Examples to make clear what I'm after, based on the precondition that the slice is drawn like a unit circle: A start angle of 0 and an end angle of PI would lead to a filled lower half of the rectangle and an empty upper half. A good solution here would be to move the center up by 1/4*h. A start angle of 0 and an end angle of PI/2 would lead to a filled bottom right quarter of the rectangle. A good solution here would be to move the center point to the top left of the rectangle and to set the radius to the smaller of both rectangle sides. This is fairly easy for the cases I've sketched but it becomes complicated when the start and end angles are arbitrary. I am searching for an algorithm which determines center of the slice and radius in a way that fills the rectangle best. Pseudo code would be great since I'm not a big mathematician.

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• How to call a method from another class that's been instantiated within the current class

  - by Pavan

  my screen has a few views like such __________________ | _____ | | | | | //viewX is a video screen | | | | | viewX | vY | | //viewY is a custom uiview i created. | |____| | //it contains a method which i would like to call that toggles |_________________| //the hidden property of this view. and when it hides, a little | | //button is replaced no the top right corner on top of viewX | viewZ | //the video layer | | |_________________| //viewZ is a view containing many square views - thumbnails. my question is, i dont know how to register for touch events so that it recognises any touch event on no matter which view the user touches the screen.. atm im handling the touch events for each view inside it. so all works well... however what im trying to do is that when the user taps anywhere else on the screen but on viewY, viewY should dissapear by calling that method in the viewY class. this viewY class is instantiated and has no xib file attached to it. the uiview is created progammatically in the viewY class. this whole class for viewY behviour is instantiated in viewX - the video view. my boss says add delegates.. although i have now clue how to do that... any help? is there anyway i can just make it really simple and be able to say REMOVE VIEW no matter which class im calling from? Also ive seen other people achieve this by using these funky arrows - ... <- etc.. although im not sure if thats what i need or how to implement such a thing. ah i think ive made my question quite complicated but i really mean it to be a simple one, and know it can be done in an easy way!

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• Creating Binary Block from struct

  - by MOnsDaR

  I hope the title is describing the problem, i'll change it if anyone has a better idea. I'm storing information in a struct like this: struct AnyStruct { AnyStruct : testInt(20), testDouble(100.01), testBool1(true), testBool2(false), testBool3(true), testChar('x') {} int testInt; double testDouble; bool testBool1; bool testBool2; bool testBool3; char testChar; std::vector<char> getBinaryBlock() { //how to build that? } } The struct should be sent via network in a binary byte-buffer with the following structure: Bit 00- 31: testInt Bit 32- 61: testDouble most significant portion Bit 62- 93: testDouble least significant portion Bit 94: testBool1 Bit 95: testBool2 Bit 96: testBool3 Bit 97-104: testChar According to this definition the resulting std::vector should have a size of 13 bytes (char == byte) My question now is how I can form such a packet out of the different datatypes I've got. I've already read through a lot of pages and found datatypes like std::bitset or boost::dynamic_bitset, but neither seems to solve my problem. I think it is easy to see, that the above code is just an example, the original standard is far more complex and contains more different datatypes. Solving the above example should solve my problems with the complex structures too i think. One last point: The problem should be solved just by using standard, portable language-features of C++ like STL or Boost (

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• Java website protection solutions (especially XSS)

  - by Mark

  I'm developing a web application, and facing some security problems. In my app users can send messages and see other's (a bulletin board like app). I'm validating all the form fields that users can send to my app. There are some very easy fields, like "nick name", that can be 6-10 alpabetical characters, or message sending time, which is sended to the users as a string, and then (when users ask for messages, that are "younger" or "older" than a date) I parse this with SimpleDateFormat (I'm developing in java, but my question is not related to only java). The big problem is the message field. I can't restrict it to only alphabetical characters (upper or lowercase), because I have to deal with some often use characters like ",',/,{,} etc... (users would not be satisfied if the system didn't allow them to use these stuff) According to this http://ha.ckers.org/xss.html, there are a lot of ways people can "hack" my site. But I'm wondering, is there any way I can do to prevent that? Not all, because there is no 100% protection, but I'd like a solution that can protect my site. I'm using servlets on the server side, and jQuery, on the client side. My app is "full" AJAX, so users open 1 JSP, then all the data is downloaded and rendered by jQuery using JSON. (yeah, I know it's not "users-without-javascript" friendly, but it's 2010, right? :-) ) I know front end validation is not enough. I'd like to use 3 layer validation: - 1. front end, javascript validate the data, then send to the server - 2. server side, the same validation, if there is anything, that shouldn't be there (because of client side javascript), I BAN the user - 3. if there is anything that I wasn't able to catch earlier, the rendering process handle and render appropriately Is there any "out of the box" solution, especially for java? Or other solution that I can use?

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• SQL query to calculate running group counts on time-phased data

  - by spong

  I have some data, like this: BUG DATE STATUS ---- ---------------------- -------- 9012 18/03/2008 9:08:44 AM OPEN 9012 18/03/2008 9:10:03 AM OPEN 9012 28/03/2008 4:55:03 PM RESOLVED 9012 28/03/2008 5:25:00 PM CLOSED 9013 18/03/2008 9:12:59 AM OPEN 9013 18/03/2008 9:15:06 AM RESOLVED 9013 18/03/2008 9:16:44 AM CLOSED 9014 18/03/2008 9:17:54 AM OPEN 9014 18/03/2008 9:18:31 AM RESOLVED 9014 18/03/2008 9:19:30 AM CLOSED 9015 18/03/2008 9:22:40 AM OPEN 9015 18/03/2008 9:23:03 AM RESOLVED 9015 19/03/2008 12:27:08 PM CLOSED 9016 18/03/2008 9:24:20 AM OPEN 9016 18/03/2008 9:24:35 AM RESOLVED 9016 19/03/2008 12:28:14 PM CLOSED 9017 18/03/2008 9:25:47 AM OPEN 9017 18/03/2008 9:26:02 AM RESOLVED 9017 19/03/2008 12:30:30 PM CLOSED Which I would like to transform into something like this: DATE OPEN RESOLVED CLOSED ---------------------- -------- -------- -------- 18/03/2008 9:08:44 AM 1 0 0 18/03/2008 9:12:59 AM 2 0 0 18/03/2008 9:15:06 AM 1 1 0 18/03/2008 9:16:44 AM 1 0 1 18/03/2008 9:17:54 AM 2 0 1 18/03/2008 9:18:31 AM 1 1 0 18/03/2008 9:19:30 AM 1 0 2 18/03/2008 9:22:40 AM 2 0 2 18/03/2008 9:23:03 AM 1 1 2 18/03/2008 9:24:20 AM 2 1 2 18/03/2008 9:24:35 AM 1 2 2 18/03/2008 9:25:47 AM 2 2 2 18/03/2008 9:26:02 AM 1 3 2 19/03/2008 12:27:08 PM 1 2 3 19/03/2008 12:28:14 PM 1 1 4 19/03/2008 12:30:30 PM 1 0 5 28/03/2008 4:55:03 PM 0 1 5 28/03/2008 5:25:00 PM 0 0 6 i.e. keeping running counts of bugs with each status. This is easy enough to code up using cursors, but I'm wondering if any of you SQL gurus out there can help with a query to achieve this? Ideally for mysql, but I'm curious to see anything that will work.

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• Creating sublines on Joomla menu items

  - by ploughansen

  In my toplevel menu items, I would like to make a subline for each item. I don't think it's possible to do by default, byt YooTheme has done it in many of their templates. The menu output look like this <div class="moduletable_menu"> <ul id="mainmenu" class="menu"> <li class="active item1" id="current"> <a href="URL_HIDDEN"> <span>Services</span> </a> </li> </ul> This basically outputs a one line menu item like so: Services What I would like to do is have a menu item like this: Services Service x, Service y, Service z For reference, have a look at the main menu on the YooTheme demo page. The way YooTheme does this, is using two pipes (||) as a linebreak, so in the Joomla backend you type "Services||Service x, Service y, Service z" as the menu title, and then there must be some fancy javascript that breaks this title into two spans, ready to be styled using css. Does anyone know of an easy way to code this? Please note that I am looking to build this feature into a custom template (ie. non-yootheme). Also note that I am not using MooTools, but Jquery instead.

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• Is there any class in the .NET Framework to represent a holding container for objects?

  - by Charles Prakash Dasari

  I am looking for a class that defines a holding structure for an object. The value for this object could be set at a later time than when this container is created. It is useful to pass such a structure in lambdas or in callback functions etc. Say: class HoldObject<T> { public T Value { get; set; } public bool IsValueSet(); public void WaitUntilHasValue(); } // and then we could use it like so ... HoldObject<byte[]> downloadedBytes = new HoldObject<byte[]>(); DownloadBytes("http://www.stackoverflow.com", sender => downloadedBytes.Value = sender.GetBytes()); It is rather easy to define this structure, but I am trying to see if one is available in FCL. I also want this to be an efficient structure that has all needed features like thread safety, efficient waiting etc. Any help is greatly appreciated.

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• Continue gif animation after escape is pressed

  - by cottsak

  Firefox (and other browsers i believe) stop gif animation when you click the Stop button or invoke it via the Escape key. I have a text input that on change makes ajax requests to update other elements. As part of this ajaxyness i have an animated gif to show feedback. I also trap the escape key press in this input so as to clear the text field for better UX. My problem is after the escape key is pressed once, none of the ajax gifs animate anymore until the page is refreshed. Does anyone know a workaround? Stuff i've tried: I tried the e.stopPropagation(); and e.cancelBubble = true; in the function handling the e.keyCode == 27 and that didn't seem to work. I suspect that this stops trigging more js events and the browser catches the escape irrespective of js activity. I have the gif showing/hiding via adding/removing a css class so it's difficult to apply the "change gif url to reset" workaround. I dont even know if this works anyway - didn't test it. But it seems difficult. If anyone knows that this works and knows of an easy way to apply the hack with background-image: url(../images/ajax-loader_dotcirclel13x13.gif); css then please let me know.

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• How to catch an incomming text message

  - by Espen

  Hi! I want to be able to control incoming text messages. My application is still on a "proof of concept" version and I'm trying to learn Android programming as I go. First my application need to catch incomming text messages. And if the message is from a known number then deal with it. If not, then send the message as nothing has happened to the default text message application. I have no doubt it can be done, but I still have some concern and I see some pitfalls at how things are done on Android. So getting the incomming text message could be fairly easy - except when there are other messaging applications installed and maybe the user wants to have normal text messages to pop up on one of them - and it will, after my application has had a look at it first. How to be sure my application get first pick of incomming text messages? And after that I need to send most text messages through to any other text message application the user has chosen so the user can actually read the message my application didn't need. Since Android uses intents that are relative at best, I don't see how I can enforce my application to get a peek at all incomming text messages, and then stop it or send it through to the default text messaging application...

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• NSData in CoreData is not saving properly

  - by abisson

  I am currently trying to store images I download from the web into an NSManagedObject class so that I don't have to redownload it every single time the application is opened. I currently have these two classes. Plant.h @property (nonatomic, retain) NSString * name; @property (nonatomic, retain) PlantPicture *picture; PlantPicture.h @property (nonatomic, retain) NSString * bucketName; @property (nonatomic, retain) NSString * creationDate; @property (nonatomic, retain) NSData * pictureData; @property (nonatomic, retain) NSString * slug; @property (nonatomic, retain) NSString * urlWithBucket; Now I do the following: - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { PlantCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath]; Plant *plant = [self.fetchedResultsController objectAtIndexPath:indexPath]; cell.plantLabel.text = plant.name; if(plant.picture.pictureData == nil) { NSLog(@"Downloading"); NSMutableString *pictureUrl = [[NSMutableString alloc]initWithString:amazonS3BaseURL]; [pictureUrl appendString:plant.picture.urlWithBucket]; NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:pictureUrl]]; AFImageRequestOperation *imageOperation = [AFImageRequestOperation imageRequestOperationWithRequest:request success:^(UIImage *image) { cell.plantImageView.image = image; plant.picture.pictureData = [[NSData alloc]initWithData:UIImageJPEGRepresentation(image, 1.0)]; NSError *error = nil; if (![_managedObjectContext save:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); } }]; [imageOperation start]; } else { NSLog(@"Already"); cell.plantImageView.image = [UIImage imageWithData:plant.picture.pictureData]; } NSLog(@"%@", plant.name); return cell; } The plant information is present, as well as the picture object. However, the NSData itself is NEVER saved throughout the application opening and closing. I always have to REDOWNLOAD the image! Any ideas!? [Very new to CoreData... sorry if it is easy!] thanks!

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• Memory management of objects returned by methods (iOS / Objective-C)

  - by iOSNewb

  I am learning Objective-C and iOS programming through the terrific iTunesU course posted by Stanford (http://www.stanford.edu/class/cs193p/cgi-bin/drupal/) Assignment 2 is to create a calculator with variable buttons. The chain of commands (e.g. 3+x-y) is stored in a NSMutableArray as "anExpression", and then we sub in random values for x and y based on an NSDictionary to get a solution. This part of the assignment is tripping me up: The final two [methods] “convert” anExpression to/from a property list: + (id)propertyListForExpression:(id)anExpression; + (id)expressionForPropertyList:(id)propertyList; You’ll remember from lecture that a property list is just any combination of NSArray, NSDictionary, NSString, NSNumber, etc., so why do we even need this method since anExpression is already a property list? (Since the expressions we build are NSMutableArrays that contain only NSString and NSNumber objects, they are, indeed, already property lists.) Well, because the caller of our API has no idea that anExpression is a property list. That’s an internal implementation detail we have chosen not to expose to callers. Even so, you may think, the implementation of these two methods is easy because anExpression is already a property list so we can just return the argument right back, right? Well, yes and no. The memory management on this one is a bit tricky. We’ll leave it up to you to figure out. Give it your best shot. Obviously, I am missing something with respect to memory management because I don't see why I can't just return the passed arguments right back. Thanks in advance for any answers!

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• Pass an array from IronRuby to C#

  - by cgyDeveloper

  I'm sure this is an easy fix and I just can't find it, but here goes: I have a C# class (let's call it Test) in an assembly (let's say SOTest.dll). Here is something along the lines of what I'm doing: private List<string> items; public List<string> list_items() { return this.items; } public void set_items(List<string> new_items) { this.items = new_items; } In the IronRuby interpreter I run: >>> require "SOTest.dll" true >>> include TestNamespace Object >>> myClass = Test.new TestNamespace.Test >>> myClass.list_items() ['Apples', 'Oranges', 'Pears'] >>> myClass.set_items ['Peaches', 'Plums'] TypeError: can't convert Array into System::Collections::Generic::List(string) I get a similar error whether I make the argument a 'List< string ', 'List< object ' or 'string[ ]'. What is the proper syntax? I can't find a documented mapping of types anywhere (because it's likely too complicated to define in certain scenarios given what Ruby can do).

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• Is the C++ compiler optimizer allowed to break my destructor ability to be called multiple times?

  - by sharptooth

  We once had an interview with a very experienced C++ developer who couldn't answer the following question: is it necessary to call the base class destructor from the derived class destructor in C++? Obviously the answer is no, C++ will call the base class destructor automagically anyway. But what if we attempt to do the call? As I see it the result will depend on whether the base class destructor can be called twice without invoking erroneous behavior. For example in this case: class BaseSafe { public: ~BaseSafe() { } private: int data; }; class DerivedSafe { public: ~DerivedSafe() { BaseSafe::~BaseSafe(); } }; everything will be fine - the BaseSafe destructor can be called twice safely and the program will run allright. But in this case: class BaseUnsafe { public: BaseUnsafe() { buffer = new char[100]; } ~BaseUnsafe () { delete[] buffer; } private: char* buffer; }; class DerivedUnsafe { public: ~DerivedUnsafe () { BaseUnsafe::~BaseUnsafe(); } }; the explicic call will run fine, but then the implicit (automagic) call to the destructor will trigger double-delete and undefined behavior. Looks like it is easy to avoid the UB in the second case. Just set buffer to null pointer after delete[]. But will this help? I mean the destructor is expected to only be run once on a fully constructed object, so the optimizer could decide that setting buffer to null pointer makes no sense and eliminate that code exposing the program to double-delete. Is the compiler allowed to do that?

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• Basic problems (type inference or something else?) in Objective-C/Cocoa.

  - by Matt

  Hi, Apologies for how basic these questions are to some. Just started learning Cocoa, working through Hillegass' book, and am trying to write my first program (a GUI Cocoa app that counts the number of characters in a string). I tried this: NSString *string = [textField stringValue]; NSUInteger *stringLength = [string length]; NSString *countString = (@"There are %u characters",stringLength); [label setStringValue:countString]; But I'm getting errors like: Incompatible pointer conversion initializing 'NSUInteger' (aka 'unsigned long'), expected 'NSUInteger *'[-pedantic] for the first line, and this for the second line: Incompatible pointer types initializing 'NSUInteger *', expected 'NSString *' [-pedantic] I did try this first, but it didn't work either: [label setStringValue:[NSString stringWithFormat:@"There are %u characters",[[textField stringValue] length]]] On a similar note, I've only written in easy scripting languages before now, and I'm not sure when I should be allocing/initing objects and when I shouldn't. For example, when is it okay to do this: NSString *myString = @"foo"; or int *length = 5; instead of this: NSString *myString = [[NSString alloc] initWithString:"foo"]; And which ones should I be putting into the header files? I did check Apple's documentation, and CocoaDev, and the book I'm working for but without luck. Maybe I'm looking in the wrong places.. Thanks to anyone who takes the time to reply this: it's appreciated, and thanks for being patient with a beginner. We all start somewhere. EDIT Okay, I tried the following again: [label setStringValue:[NSString stringWithFormat:@"There are %u characters",[[textField stringValue] length]]] And it actually worked this time. Not sure why it didn't the first time, though I think I might have typed %d instead of %u by mistake. However I still don't understand why the code I posted at the top of my original post doesn't work, and I have no idea what the errors mean, and I'd very much like to know because it seems like I'm missing something important there.

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• @selector and return value

  - by user320926

  The idea it's very easy, i have an http download class, this class must support the http authentication but it's basically a background thread so i would like to avoid to prompt directly to the screen, i would like to use a delegate method to require from outside of the class, like a viewController. But i don't know if is possible or if i have to use a different syntax. This class use this delegate protocol: //Updater.h @protocol Updater <NSObject> -(NSDictionary *)authRequired; @optional -(void)statusUpdate:(NSString *)newStatus; -(void)downloadProgress:(int)percentage; @end @interface Updater : NSThread { ... } This is the call to the delegate method: //Updater.m // This check always fails :( if ([self.delegate respondsToSelector:@selector(authRequired:)]) { auth = [delegate authRequired]; } This is the implementation of the delegate method //rootViewController.m -(NSDictionary *)authRequired; { // TODO: some kind of popup or modal view NSMutableDictionary *ret=[[NSMutableDictionary alloc] init]; [ret setObject:@"utente" forKey:@"user"]; [ret setObject:@"password" forKey:@"pass"]; return ret; }

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• How to detect what allowed character in current Regular Expression by using JavaScript?

  - by Soul_Master

  In my web application, I create some framework that use to bind model data to control on page. Each model property has some rule like string length, not null and regular expression. Before submit page, framework validate any binded control with defined rules. So, I want to detect what character that is allowed in each regular expression rule like the following example. "^[0-9]$" allow only digit characters like 1, 2, 3. "^[a-zA-Z_][a-zA-Z_-0-9]+$" allow only a-z, - and _ characters However, this function should not care about grouping, positioning of allowed character. It just tells about possible characters only. By the way, complex regular expression like find two words near(\bword1\W+(?:\w+\W+){1,6}?word2\b) must be ignore to verify and it should return any characters is possible. Do you have any idea for creating this function? PS. I know it easy to create specified function like numeric only for allowing only digit characters. But I need share/reuse same piece of code both data tier(contains all model validator) and UI tier without modify anything. Thanks

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• Is there anything inherently wrong with long variable/method names in Java?

  - by Doug Smith

  I know this is probably is a question of personal opinion, but I want to know what's standard practice and what would be frowned upon. One of my profs in university always seems to make his variable and method names as short as possible (getAmt() instead of getAmount) for instance. I have no objection to this, but personally, I prefer to have mine a little longer if it adds descriptiveness so the person reading it won't have to check or refer to documentation. For instance, we made a method that given a list of players, returns the player who scored the most goals. I made the method getPlayerWithMostGoals(), is this wrong? I toiled over choosing a way to make it shorter for awhile, but then I thought "why?". It gets the point across clearly and Eclipse makes it easy to autocomplete it when I type. I'm just wondering if the short variable names are a piece of the past due to needing everything to be as small as possible to be efficient. Is this still a requirement?

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• GUID or int entity key with SQL Compact/EF4?

  - by David Veeneman

  This is a follow-up to an earlier question I posted on EF4 entity keys with SQL Compact. SQL Compact doesn't allow server-generated identity keys, so I am left with creating my own keys as objects are added to the ObjectContext. My first choice would be an integer key, and the previous answer linked to a blog post that shows an extension method that uses the Max operator with a selector expression to find the next available key: public static TResult NextId<TSource, TResult>(this ObjectSet<TSource> table, Expression<Func<TSource, TResult>> selector) where TSource : class { TResult lastId = table.Any() ? table.Max(selector) : default(TResult); if (lastId is int) { lastId = (TResult)(object)(((int)(object)lastId) + 1); } return lastId; } Here's my take on the extension method: It will work fine if the ObjectContext that I am working with has an unfiltered entity set. In that case, the ObjectContext will contain all rows from the data table, and I will get an accurate result. But if the entity set is the result of a query filter, the method will return the last entity key in the filtered entity set, which will not necessarily be the last key in the data table. So I think the extension method won't really work. At this point, the obvious solution seems to be to simply use a GUID as the entity key. That way, I only need to call Guid.NewGuid() method to set the ID property before I add a new entity to my ObjectContext. Here is my question: Is there a simple way of getting the last primary key in the data store from EF4 (without having to create a second ObjectContext for that purpose)? Any other reason not to take the easy way out and simply use a GUID? Thanks for your help.

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