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• Segmenting a double array of labels

  - by Ami

  The Problem: I have a large double array populated with various labels. Each element (cell) in the double array contains a set of labels and some elements in the double array may be empty. I need an algorithm to cluster elements in the double array into discrete segments. A segment is defined as a set of pixels that are adjacent within the double array and one label that all those pixels in the segment have in common. (Diagonal adjacency doesn't count and I'm not clustering empty cells). |-------|-------|------| | Jane | Joe | | | Jack | Jane | | |-------|-------|------| | Jane | Jane | | | | Joe | | |-------|-------|------| | | Jack | Jane | | | Joe | | |-------|-------|------| In the above arrangement of labels distributed over nine elements, the largest cluster is the “Jane” cluster occupying the four upper left cells. What I've Considered: I've considered iterating through every label of every cell in the double array and testing to see if the cell-label combination under inspection can be associated with a preexisting segment. If the element under inspection cannot be associated with a preexisting segment it becomes the first member of a new segment. If the label/cell combination can be associated with a preexisting segment it associates. Of course, to make this method reasonable I'd have to implement an elaborate hashing system. I'd have to keep track of all the cell-label combinations that stand adjacent to preexisting segments and are in the path of the incrementing indices that are iterating through the double array. This hash method would avoid having to iterate through every pixel in every preexisting segment to find an adjacency. Why I Don't Like it: As is, the above algorithm doesn't take into consideration the case where an element in the double array can be associated with two unique segments, one in the horizontal direction and one in the vertical direction. To handle these cases properly, I would need to implement a test for this specific case and then implement a method that will both associate the element under inspection with a segment and then concatenate the two adjacent identical segments. On the whole, this method and the intricate hashing system that it would require feels very inelegant. Additionally, I really only care about finding the large segments in the double array and I'm much more concerned with the speed of this algorithm than with the accuracy of the segmentation, so I'm looking for a better way. I assume there is some stochastic method for doing this that I haven't thought of. Any suggestions?

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• How to work with file and streams in php,case: if we open file in Class A and pass open stream to Cl

  - by Rachel

  I have two class, one is Business Logic Class{BLO} and the other one is Data Access Class{DAO} and I have dependency in my BLO class to my Dao class. Basically am opening a csv file to write into it in my BLO class using inside its constructor as I am creating an object of BLO and passing in file from command prompt: Code: $this->fin = fopen($file,'w+') or die('Cannot open file'); Now inside BLO I have one function notifiy, which call has dependency to DAO class and call getCurrentDBSnapshot function from the Dao and passes the open stream so that data gets populated into the stream. Code: Blo Class Constructor: public function __construct($file) { //Open Unica File for parsing. $this->fin = fopen($file,'w+') or die('Cannot open file'); // Initialize the Repository DAO. $this->dao = new Dao('REPO'); } Blo Class method that interacts with Dao Method and call getCurrentDBSnapshot. public function notifiy() { $data = $this->fin; var_dump($data); //resource(9) of type (stream) $outputFile=$this->dao->getCurrentDBSnapshot($data); // So basically am passing in $data which is resource((9) of type (stream) } Dao function: getCurrentDBSnapshot which get current state of Database table. public function getCurrentDBSnapshot($data) { $query = "SELECT * FROM myTable"; //Basically just preparing the query. $stmt = $this->connection->prepare($query); // Execute the statement $stmt->execute(); $header = array(); while ($row=$stmt->fetch(PDO::FETCH_ASSOC)) { if(empty($header)) { // Get the header values from table(columnnames) $header = array_keys($row); // Populate csv file with header information from the mytable fputcsv($data, $header); } // Export every row to a file fputcsv($data, $row); } var_dump($data);//resource(9) of type (stream) return $data; } So basically in am getting back resource(9) of type (stream) from getCurrentDBSnapshot and am storing that stream into $outputFile in Blo class method notify. Now I want to close the file which I opened for writing and so it should be fclose of $outputFile or $data, because in both the cases it gives me: var_dump(fclose($outputFile)) as bool(false) var_dump(fclose($data)) as bool(false) and var_dump($outputFile) as resource(9) of type (Unknown) var_dump($data) as resource(9) of type (Unknown) My question is that if I open file using fopen in class A and if I call class B method from Class A method and pass an open stream, in our case $data, than Class B would perform some work and return back and open stream and so How can I close that open stream in Class A's method or it is ok to keep that stream open and not use fclose ? Would appreciate inputs as am not very sure as how this can be implemented.

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• Can anyone explain me the source code of python "import this"?

  - by byterussian

  If you open a Python interpreter, and type "import this", as you know, it prints: The Zen of Python, by Tim Peters Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparse is better than dense. Readability counts. Special cases aren't special enough to break the rules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. There should be one-- and preferably only one --obvious way to do it. Although that way may not be obvious at first unless you're Dutch. Now is better than never. Although never is often better than *right* now. If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea. Namespaces are one honking great idea -- let's do more of those! In the python source(Lib/this.py) this text is generated by a curios piece of code: s = """Gur Mra bs Clguba, ol Gvz Crgref Ornhgvshy vf orggre guna htyl. Rkcyvpvg vf orggre guna vzcyvpvg. Fvzcyr vf orggre guna pbzcyrk. Pbzcyrk vf orggre guna pbzcyvpngrq. Syng vf orggre guna arfgrq. Fcnefr vf orggre guna qrafr. Ernqnovyvgl pbhagf. Fcrpvny pnfrf nera'g fcrpvny rabhtu gb oernx gur ehyrf. Nygubhtu cenpgvpnyvgl orngf chevgl. Reebef fubhyq arire cnff fvyragyl. Hayrff rkcyvpvgyl fvyraprq. Va gur snpr bs nzovthvgl, ershfr gur grzcgngvba gb thrff. Gurer fubhyq or bar-- naq cersrenoyl bayl bar --boivbhf jnl gb qb vg. Nygubhtu gung jnl znl abg or boivbhf ng svefg hayrff lbh'er Qhgpu. Abj vf orggre guna arire. Nygubhtu arire vf bsgra orggre guna *evtug* abj. Vs gur vzcyrzragngvba vf uneq gb rkcynva, vg'f n onq vqrn. Vs gur vzcyrzragngvba vf rnfl gb rkcynva, vg znl or n tbbq vqrn. Anzrfcnprf ner bar ubaxvat terng vqrn -- yrg'f qb zber bs gubfr!""" d = {} for c in (65, 97): for i in range(26): d[chr(i+c)] = chr((i+13) % 26 + c) print "".join([d.get(c, c) for c in s])

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• stop and split generated sequence at repeats - clojure

  - by fitzsnaggle

  I am trying to make a sequence that will only generate values until it finds the following conditions and return the listed results: case head = 0 - return {:origin [all generated except 0] :pattern 0} 1 - return {:origin nil :pattern [all-generated-values] } repeated-value - {:origin [values-before-repeat] :pattern [values-after-repeat] { ; n = int ; x = int ; hist - all generated values ; Keeps the head below x (defn trim-head [head x] (loop [head head] (if (> head x) (recur (- head x)) head))) ; Generates the next head (defn next-head [head x n] (trim-head (* head n) x)) (defn row [x n] (iterate #(next-head % x n) n)) ; Generates a whole row - ; Rows are a max of x - 1. (take (- x 1) (row 11 3)) Examples of cases to stop before reaching end of row: [9 8 4 5 6 7 4] - '4' is repeated so STOP. Return preceding as origin and rest as pattern. {:origin [9 8] :pattern [4 5 6 7]} [4 5 6 1] - found a '1' so STOP, so return everything as pattern {:origin nil :pattern [4 5 6 1]} [3 0] - found a '0' so STOP {:origin [3] :pattern [0]} :else if the sequences reaches a length of x - 1: {:origin [all values generated] :pattern nil} The Problem I have used partition-by with some success to split the groups at the point where a repeated value is found, but would like to do this lazily. Is there some way I can use take-while, or condp, or the :while clause of the for loop to make a condition that partitions when it finds repeats? Some Attempts (take 2 (partition-by #(= 1 %) (row 11 4))) (for [p (partition-by #(stop-match? %) head) (iterate #(next-head % x n) n) :while (or (not= (last p) (or 1 0 n) (nil? (rest p))] {:origin (first p) :pattern (concat (second p) (last p))})) # Updates What I really want to be able to do is find out if a value has repeated and partition the seq without using the index. Is that possible? Something like this - { (defn row [x n] (loop [hist [n] head (gen-next-head (first hist) x n) steps 1] (if (>= (- x 1) steps) (case head 0 {:origin [hist] :pattern [0]} 1 {:origin nil :pattern (conj hist head)} ; Speculative from here on out (let [p (partition-by #(apply distinct? %) (conj hist head))] (if-not (nil? (next p)) ; One partition if no repeats. {:origin (first p) :pattern (concat (second p) (nth 3 p))} (recur (conj hist head) (gen-next-head head x n) (inc steps))))) {:origin hist :pattern nil}))) }

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• Django Encoding Issues with MySQL

  - by Jordan Reiter

  Okay, so I have a MySQL database set up. Most of the tables are latin1 and Django handles them fine. But, some of them are UTF-8 and Django does not handle them. Here's a sample table (these tables are all from django-geonames): DROP TABLE IF EXISTS `geoname`; SET @saved_cs_client = @@character_set_client; SET character_set_client = utf8; CREATE TABLE `geoname` ( `id` int(11) NOT NULL, `name` varchar(200) NOT NULL, `ascii_name` varchar(200) NOT NULL, `latitude` decimal(20,17) NOT NULL, `longitude` decimal(20,17) NOT NULL, `point` point default NULL, `fclass` varchar(1) NOT NULL, `fcode` varchar(7) NOT NULL, `country_id` varchar(2) NOT NULL, `cc2` varchar(60) NOT NULL, `admin1_id` int(11) default NULL, `admin2_id` int(11) default NULL, `admin3_id` int(11) default NULL, `admin4_id` int(11) default NULL, `population` int(11) NOT NULL, `elevation` int(11) NOT NULL, `gtopo30` int(11) NOT NULL, `timezone_id` int(11) default NULL, `moddate` date NOT NULL, PRIMARY KEY (`id`), KEY `country_id_refs_iso_alpha2_e2614807` (`country_id`), KEY `admin1_id_refs_id_a28cd057` (`admin1_id`), KEY `admin2_id_refs_id_4f9a0f7e` (`admin2_id`), KEY `admin3_id_refs_id_f8a5e181` (`admin3_id`), KEY `admin4_id_refs_id_9cc00ec8` (`admin4_id`), KEY `fcode_refs_code_977fe2ec` (`fcode`), KEY `timezone_id_refs_id_5b46c585` (`timezone_id`), KEY `geoname_52094d6e` (`name`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; SET character_set_client = @saved_cs_client; Now, if I try to get data from the table directly using MySQLdb and a cursor, I get the text with the proper encoding: >>> import MySQLdb >>> from django.conf import settings >>> >>> conn = MySQLdb.connect (host = "localhost", ... user = settings.DATABASES['default']['USER'], ... passwd = settings.DATABASES['default']['PASSWORD'], ... db = settings.DATABASES['default']['NAME']) >>> cursor = conn.cursor () >>> cursor.execute("select name from geoname where name like 'Uni%Hidalgo'"); 1L >>> g = cursor.fetchone() >>> g[0] 'Uni\xc3\xb3n Hidalgo' >>> print g[0] Unión Hidalgo However, if I try to use the Geoname model (which is actually a django.contrib.gis.db.models.Model), it fails: >>> from geonames.models import Geoname >>> g = Geoname.objects.get(name__istartswith='Uni',name__icontains='Hidalgo') >>> g.name u'Uni\xc3\xb3n Hidalgo' >>> print g.name Unión Hidalgo There's pretty clearly an encoding error here. In both cases the database is returning 'Uni\xc3\xb3n Hidalgo' but Django is (incorrectly?) translating the '\xc3\xb3n' to ó. What can I do to fix this?

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• Mass Ball-to-Ball Collision Handling (as in, lots of balls)

  - by BlueThen

  Update: Found out that I was using the radius as the diameter, which was why the mtd was overcompensating. Hi, StackOverflow. I've written a Processing program awhile back simulating ball physics. Basically, I have a large number of balls (1000), with gravity turned on. Detection works great, but my issue is that they start acting weird when they're bouncing against other balls in all directions. I'm pretty confident this involves the handling. For the most part, I'm using Jay Conrod's code. One part that's different is if (distance > 1.0) return; which I've changed to if (distance < 1.0) return; because the collision wasn't even being performed with the first bit of code, I'm guessing that's a typo. The balls overlap when I use his code, which isn't what I was looking for. My attempt to fix it was to move the balls to the edge of each other: float angle = atan2(y - collider.y, x - collider.x); float distance = dist(x,y, balls[ID2].x,balls[ID2].y); x = collider.x + radius * cos(angle); y = collider.y + radius * sin(angle); This isn't correct, I'm pretty sure of that. I tried the correction algorithm in the previous ball-to-ball topic: // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); except my version doesn't use vectors, and every ball's weight is 1. The resulting code I get is this: PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.5; y -= mtd.y * 0.5; collider.x += mtd.x * 0.5; collider.y += mtd.y * 0.5; This code seems to over-correct collisions. Which doesn't make sense to me because in no other way do I modify the x and y values of each ball, other than this. Some other part of my code could be wrong, but I don't know. Here's the snippet of the entire ball-to-ball collision handling I'm using: if (alreadyCollided.contains(new Integer(ID2))) // if the ball has already collided with this, then we don't need to reperform the collision algorithm return; Ball collider = (Ball) objects.get(ID2); PVector collision = new PVector(x - collider.x, y - collider.y); float distance = collision.mag(); if (distance == 0) { collision = new PVector(1,0); distance = 1; } if (distance < 1) return; PVector velocity = new PVector(vx,vy); PVector velocity2 = new PVector(collider.vx, collider.vy); collision.div(distance); // normalize the distance float aci = velocity.dot(collision); float bci = velocity2.dot(collision); float acf = bci; float bcf = aci; vx += (acf - aci) * collision.x; vy += (acf - aci) * collision.y; collider.vx += (bcf - bci) * collision.x; collider.vy += (bcf - bci) * collision.y; alreadyCollided.add(new Integer(ID2)); collider.alreadyCollided.add(new Integer(ID)); PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.2; y -= mtd.y * 0.2; collider.x += mtd.x * 0.2; collider.y += mtd.y * 0.2; Thanks. (Apologies for lack of sources, stackoverflow thinks I'm a spammer)

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• PHP max_execution_time not timing out

  - by Joey Ezekiel

  This is not one of the regular questions if sleep is counted for timeout or stuff like that. Ok, here's the problem: I've set the max_execution_time for PHP as 15 seconds and ideally this should time out when it crosses the set limit, but it doesn't. Apache has been restarted after the change to the php.ini file and an ini_get('max_execution_time') is all fine. Sometimes the script runs for upto 200 seconds which is crazy. I have no database communication whatsoever. All the script does is looking for files on the unix filesystem and in some cases re-directing to another JSP page. There is no sleep() on the script. I calculate the total execution time of the PHP script like this: At the start of the script I set : $_mtime = microtime(); $_mtime = explode(" ",$_mtime); $_mtime = $_mtime[1] + $_mtime[0]; $_gStartTime = $_mtime; and the end time($_gEndTime) is calculated similarly. The total time is calculated in a shutdown function that I've registered: register_shutdown_function('shutdown'); ............. function shutdown() { .............. .............. $_total_time = $_gEndTime - $_gStartTime; .............. switch (connection_status ()) { case CONNECTION_NORMAL: .... break; .... case CONNECTION_TIMEOUT: .... break; ...... } } Note: I cannot use $_SERVER['REQUEST_TIME'] because my PHP version is incompatible. That sucks - I know. 1) Well, my first question obviously is is why is my PHP script executing even after the set timeout limit? 2) Apache has the Timeout directive which is 300 seconds but the PHP binary does not read the Apache config and this should not be a problem. 3) Is there a possibility that something is sending PHP into a sleep mode? 4) Am I calculating the execution time in a wrong way? Is there a better way to do this? I'm stumped at this point. PHP Wizards - please help.

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• OpenGL suppresses exceptions in MFC dialog-based application

  - by Mikhail

  Hello. I have an MFC-driven dialog-based application created with MSVS2005. Here is my problem step by step. I have button on my dialog and corresponding click-handler with code like this: int* i = 0; *i = 3; I'm running debug version of program and when I click on the button, Visual Studio catches focus and alerts "Access violation writing location" exception, program cannot recover from the error and all I can do is to stop debugging. And this is the right behavior. Now I add some OpenGL initialization code in the OnInitDialog() method: HDC DC = GetDC(GetSafeHwnd()); static PIXELFORMATDESCRIPTOR pfd = { sizeof(PIXELFORMATDESCRIPTOR), // size of this pfd 1, // version number PFD_DRAW_TO_WINDOW | // support window PFD_SUPPORT_OPENGL | // support OpenGL PFD_DOUBLEBUFFER, // double buffered PFD_TYPE_RGBA, // RGBA type 24, // 24-bit color depth 0, 0, 0, 0, 0, 0, // color bits ignored 0, // no alpha buffer 0, // shift bit ignored 0, // no accumulation buffer 0, 0, 0, 0, // accum bits ignored 32, // 32-bit z-buffer 0, // no stencil buffer 0, // no auxiliary buffer PFD_MAIN_PLANE, // main layer 0, // reserved 0, 0, 0 // layer masks ignored }; int pixelformat = ChoosePixelFormat(DC, &pfd); SetPixelFormat(DC, pixelformat, &pfd); HGLRC hrc = wglCreateContext(DC); ASSERT(hrc != NULL); wglMakeCurrent(DC, hrc); Of course this is not exactly what I do, it is the simplified version of my code. Well now the strange things begin to happen: all initialization is fine, there are no errors in OnInitDialog(), but when I click the button... no exception is thrown. Nothing happens. At all. If I set a break-point at the *i = 3; and press F11 on it, the handler-function halts immediately and focus is returned to the application, which continue to work well. I can click button again and the same thing will happen. It seems like someone had handled occurred exception of access violation and silently returned execution into main application message-receiving cycle. If I comment the line wglMakeCurrent(DC, hrc);, all works fine as before, exception is thrown and Visual Studio catches it and shows window with error message and program must be terminated afterwards. I experience this problem under Windows 7 64-bit, NVIDIA GeForce 8800 with latest drivers (of 11.01.2010) available at website installed. My colleague has Windows Vista 32-bit and has no such problem - exception is thrown and application crashes in both cases. Well, hope good guys will help me :) PS The problem originally where posted under this topic.

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• Opinion on "loop invariants", and are these frequently used in the industry?

  - by Michael Aaron Safyan

  I was thinking back to my freshman year at college (five years ago) when I took an exam to place-out of intro-level computer science. There was a question about loop invariants, and I was wondering if loop invariants are really necessary in this case or if the question was simply a bad example... the question was to write an iterative definition for a factorial function, and then to prove that the function was correct. The code that I provided for the factorial function was as follows: public static int factorial(int x) { if ( x < 0 ){ throw new IllegalArgumentException("Parameter must be = 0"); }else if ( x == 0 ){ return 1; }else{ int result = 1; for ( int i = 1; i <= x; i++ ){ result*=i; } return result; } } My own proof of correctness was a proof by cases, and in each I asserted that it was correct by definition (x! is undefined for negative values, 0! is 1, and x! is 1*2*3...*x for a positive value of x). The professor wanted me to prove the loop using a loop invariant; however, my argument was that it was correct "by definition", because the definition of "x!" for a positive integer x is "the product of the integers from 1... x", and the for-loop in the else clause is simply a literal translation of this definition. Is a loop invariant really needed as a proof of correctness in this case? How complicated must a loop be before a loop invariant (and proper initialization and termination conditions) become necessary for a proof of correctness? Additionally, I was wondering... how often are such formal proofs used in the industry? I have found that about half of my courses are very theoretical and proof-heavy and about half are very implementation and coding-heavy, without any formal or theoretical material. How much do these overlap in practice? If you do use proofs in the industry, when do you apply them (always, only if it's complicated, rarely, never)?

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• How safe is my safe rethrow?

  - by gustafc

  (Late edit: This question will hopefully be obsolete when Java 7 comes, because of the "final rethrow" feature which seems like it will be added.) Quite often, I find myself in situations looking like this: do some initialization try { do some work } catch any exception { undo initialization rethrow exception } In C# you can do it like this: InitializeStuff(); try { DoSomeWork(); } catch { UndoInitialize(); throw; } For Java, there's no good substitution, and since the proposal for improved exception handling was cut from Java 7, it looks like it'll take at best several years until we get something like it. Thus, I decided to roll my own: (Edit: Half a year later, final rethrow is back, or so it seems.) public final class Rethrow { private Rethrow() { throw new AssertionError("uninstantiable"); } /** Rethrows t if it is an unchecked exception. */ public static void unchecked(Throwable t) { if (t instanceof Error) throw (Error) t; if (t instanceof RuntimeException) throw (RuntimeException) t; } /** Rethrows t if it is an unchecked exception or an instance of E. */ public static <E extends Exception> void instanceOrUnchecked( Class<E> exceptionClass, Throwable t) throws E, Error, RuntimeException { Rethrow.unchecked(t); if (exceptionClass.isInstance(t)) throw exceptionClass.cast(t); } } Typical usage: public void doStuff() throws SomeException { initializeStuff(); try { doSomeWork(); } catch (Throwable t) { undoInitialize(); Rethrow.instanceOrUnchecked(SomeException.class, t); // We shouldn't get past the above line as only unchecked or // SomeException exceptions are thrown in the try block, but // we don't want to risk swallowing an error, so: throw new SomeException("Unexpected exception", t); } private void doSomeWork() throws SomeException { ... } } It's a bit wordy, catching Throwable is usually frowned upon, I'm not really happy at using reflection just to rethrow an exception, and I always feel a bit uneasy writing "this will not happen" comments, but in practice it works well (or seems to, at least). What I wonder is: Do I have any flaws in my rethrow helper methods? Some corner cases I've missed? (I know that the Throwable may have been caused by something so severe that my undoInitialize will fail, but that's OK.) Has someone already invented this? I looked at Commons Lang's ExceptionUtils but that does other things. Edit: finally is not the droid I'm looking for. I'm only interested to do stuff when an exception is thrown. Yes, I know catching Throwable is a big no-no, but I think it's the lesser evil here compared to having three catch clauses (for Error, RuntimeException and SomeException, respectively) with identical code. Note that I'm not trying to suppress any errors - the idea is that any exceptions thrown in the try block will continue to bubble up through the call stack as soon as I've rewinded a few things.

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• How to catch 'exceptions' for out of order execution in Workflow Foundation 4?

  - by Alex Key

  Hi, I am attempting to model a worklfow using a "WCF Workflow Service" in .net / vs 2010 that needs to handle out of order execution gracefully (but not allow it - if thath makes sense!?) For example I have 2 receive activities one called Initialize and the other called GetValue inside a FlowChart. In most cases Initialize should be called first and GetValue after (as modled in the flow chart). However if GetValue is executed before Initialize I do not want to return an "out of order" exception (although when I look at the WCF test client, I can't actually see an exception). But instead a custom exception saying something like "you must initialize first". In theory I could model this with lots of parallel activities and conditions to check if Initialized / Running / Terminated etc. But the business process I am modelling if very very similar to a state machine... except it must handle people executing things in the wrong order. Ideally I would like to catch the "out of order" exception (thought I don't think it's really an exception as such), check the 'exception' to see which function was attempted to run and then handle it. I have done some research around enabling AllowBufferedReceive. However I don't want to be able to execute out of order (I don't think), but instead give a detailed response if it does happen. I've looked at the new beta state machine template for WF 4 - but i'm not sure if it does what i'm after? I'm not sure if I have the wrong end of the stick, so any help would be greatly appreciated. [EDIT] To help clarify... Sorry it's a tricky one to explain. The standard I am trying to implement (the e-learning standard SCORM RTE) is structured like a state machine i.e. certain functions can only be executed in certain states. However the standard specifies that if the calling clients tries to execute a function that it is not meant to, then a warning should be issued... for example "you cannot use GetValue(), because you have not yet Initialized". Ideally I'd like to structure the workflow as the theoretical state machine and not need to have to use multiple if/else's to handle all the scenarios where something could be executed out-of-order. I'd like to catch a out-of-order exception (but I don't think there is such an exception - as it's not in the debugger) and rethrow it.

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• How can I make the C# compiler infer these type parameters automatically?

  - by John Feminella

  I have some code that looks like the following. First I have some domain classes and some special comparators for them. public class Fruit { public int Calories { get; set; } public string Name { get; set; } } public class FruitEqualityComparer : IEqualityComparer<Fruit> { // ... } public class BasketEqualityComparer : IEqualityComparer<IEnumerable<Fruit>> { // ... } Next, I have a helper class called ConstraintChecker. It has a simple BaseEquals method that makes sure some simple base cases are considered: public static class ConstraintChecker { public static bool BaseEquals(T lhs, T rhs) { bool sameObject = l == r; bool leftNull = l == null; bool rightNull = r == null; return sameObject && !leftNull && !rightNull; } There's also a SemanticEquals method which is just a BaseEquals check and a comparator function that you specify. public static bool SemanticEquals<T>(T lhs, T rhs, Func<T, T, bool> f) { return BaseEquals(lhs, rhs) && f(lhs, rhs); } And finally there's a SemanticSequenceEquals method which accepts two IEnumerable<T> instances to compare, and an IEqualityComparer instance that will get called on each pair of elements in the list via Enumerable.SequenceEquals. public static bool SemanticSequenceEquals<T, U, V>(U lhs, U rhs, V comparator) where U : IEnumerable<T> where V : IEqualityComparer<T> { return SemanticEquals(lhs, rhs, (l, r) => lhs.SequenceEqual(rhs, comparator)); } } // end of ConstraintChecker The point of SemanticSequenceEquals is that you don't have to define two comparators whenever you want to compare both IEnumerable<T> and T instances; now you can just specify an IEqualityComparer<T> and it will also handle lists when you invoke SemanticSequenceEquals. So I could get rid of the BasketEqualityComparer class, which would be nice. But there's a problem. The C# compiler can't figure out the types involved when you invoke SemanticSequenceEquals: return ConstraintChecker.SemanticSequenceEquals(lhs, rhs, new FruitEqualityComparer()); If I specify them explicitly, it works: return ConstraintChecker.SemanticSequenceEquals< Fruit, IEnumerable<Fruit>, IEqualityComparer<Fruit> > (lhs, rhs, new FruitEqualityComparer()); What can I change here so that I don't have to write the type parameters explicitly?

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• SSL confirmation dialog popup auto closes in IE8 when re-accessing a JNLP file

  - by haylem

  I'm having this very annoying problem to troubleshoot and have been going at it for way too many days now, so have a go at it. The Environment We have 2 app-servers, which can be located on either the same machine or 2 different machines, and use the same signing certificate, and host 2 different web-apps. Though let's say, for the sake of our study case here, that they are on the same physical machine. So, we have: https://company.com/webapp1/ https://company.com/webapp2/ webapp1 is GWT-based rich-client which contains on one of its screens a menu with an item that is used to invoke a Java WebStart Client located on webapp2. It does so by performing a simple window.open call via this GWT call: Window.open("https://company.com/webapp2/app.jnlp", "_blank", null); Expected Behavior User merrilly goes to webapp1 User navigates to menu entry to start the WebStart app and clicks on it browser fires off a separate window/dialog which, depending on the browser and its security settings, will: request confirmation to navigate to this secure site, directly download the file, and possibly auto-execute a javaws process if there's a file association, otherwise the user can simply click on the file and start the app (or go about doing whatever it takes here). If you close the app, close the dialog, and re-click the menu entry, the same thing should happen again. Actual Behavior On Anything but God-forsaken IE 8 (Though I admit there's also all the god-forsaken pre-IE8 stuff, but the Requirements Lords being merciful we have already recently managed to make them drop these suckers. That was close. Let's hold hands and say a prayer of gratitude.) Stuff just works. JNLP gets downloaded, app executes just fine, you can close the app and re-do all the steps and it will restart happily. People rejoice. Puppies are safe and play on green hills in the sunshine. Developers can go grab a coffee and move on to more meaningful and rewarding tasks, like checking out on SO questions. Chrome doesn't want to execute the JNLP, but who cares? Customers won't get RSI from clicking a file every other week. On God-forsaken IE8 On the first visit, the dialog opens and requests confirmation for the user to continue to webapp2, though it could be unsafe (here be dragons, I tell you). The JNLP downloads and auto-opens, the app start. Your breathing is steady and slow. You close the app, close that SSL confirmation dialog, and re-click the menu entry. The dialog opens and auto-closes. Nothing starts, the file wasn't downloaded to any known location and Fiddler just reports the connection was closed. If you close IE and reach that menu item to click it again, it is now back to working correctly. Until you try again during the same session, of course. Your heart-rate goes up, you get some more coffee to make matters worse, and start looking for plain tickets online and a cheap but heavy golf-club on an online auction site to go clubbing baby polar seals to avenge your bloodthirst, as the gates to the IE team in Redmond are probably more secured than an ice block, as one would assume they get death threats often. Plus, the IE9 and IE10 teams are already hard at work fxing the crap left by their predecessors, so maybe you don't want to be too hard on them, and you don't have money to waste on a PI to track down the former devs responsible for this mess. Added Details I have come across many problems with IE8 not downloading files over SSL when it uses a no-cache header. This was indeed one of our problems, which seems to be worked out now. It downloads files fine, webapp2 uses the following headers to serve the JNLP file: response.setHeader("Cache-Control", "private, must-revalidate"); // IE8 happy response.setHeader("Pragma", "private"); // IE8 happy response.setHeader("Expires", "0"); // IE8 happy response.setHeader("Access-Control-Allow-Origin", "*"); // allow to request via cross-origin AJAX response.setContentType("application/x-java-jnlp-file"); // please exec me As you might have inferred, we get some confirmation dialog because there's something odd with the SSL certificate. Unfortunately I have no control over that. Assuming that's only temporary and for development purposes as we usually don't get our hands on the production certs. So the SSL cert is expired and doesn't specify the server. And the confirmation dialog. Wouldn't be that bad if it weren't for IE, as other browsers don't care, just ask for confirmation, and execute as expected and consistantly. Please, pretty please, help me, or I might consider sacrificial killings as an option. And I think I just found a decently prized stainless steel golf-club, so I'm right on the edge of gore. Side Notes Might actually be related to IE8 window.open SSL Certificate issue. Though it doesn't explain why the dialog would auto-close (that really is beyong me...), it could help to not have the confirmation dialog and not need the dialog at all. For instance, I was thinking that just having a simple URL in that menu instead of have it entirely managed by GWT code to invoke a Window.open would solve the problem. But I don't have control on that menu, and also I'm very curious how this could be fixed otherwise and why the hell it happens in the first place...

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• WCF Service Library - make calls from Console App

  - by inutan

  Hello there, I have a WCF Service Library with netTcpBinding. Its app.config as follows: <configuration> <system.serviceModel> <bindings> <netTcpBinding> <binding name="netTcp" maxBufferPoolSize="50000000" maxReceivedMessageSize="50000000"> <readerQuotas maxDepth="500" maxStringContentLength="50000000" maxArrayLength="50000000" maxBytesPerRead="50000000" maxNameTableCharCount="50000000" /> <security mode="None"></security> </binding> </netTcpBinding> </bindings> <services> <service behaviorConfiguration="ReportingComponentLibrary.TemplateServiceBehavior" name="ReportingComponentLibrary.TemplateReportService"> <endpoint address="TemplateService" binding="netTcpBinding" bindingConfiguration="netTcp" contract="ReportingComponentLibrary.ITemplateService"></endpoint> <endpoint address="ReportService" binding="netTcpBinding" bindingConfiguration="netTcp" contract="ReportingComponentLibrary.IReportService"/> <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" ></endpoint> <host> <baseAddresses> <add baseAddress="net.tcp://localhost:8001/TemplateReportService" /> <add baseAddress ="http://localhost:8080/TemplateReportService" /> </baseAddresses> </host> </service> </services> <behaviors> <serviceBehaviors> <behavior name="ReportingComponentLibrary.TemplateServiceBehavior"> <serviceMetadata httpGetEnabled="True"/> <serviceDebug includeExceptionDetailInFaults="True" /> </behavior> </serviceBehaviors> </behaviors> </system.serviceModel> </configuration> I want to call it from a console application for testing purpose. I understand that I can call by adding Service Reference or by adding proxy using svcutil. But in both these cases, my service needs to be up and running (I used WCF Test Client) Is there any other way I can call and test service method from console application?

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• NSMutableURLRequest and a Password with special Characters won't work

  - by twickl

  I'm writing a small program (using Cocoa Touch), which communicates with a webservice. The code for calling the webservice, is the following: - (IBAction)send:(id)sender { if ([number.text length] > 0) { [[UIApplication sharedApplication] beginIgnoringInteractionEvents]; [activityIndicator startAnimating]; NSString *modded; modded = [self computeNumber]; NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL: [NSURL URLWithString:@"https://tester:%=&[email protected]/RPC2"]]; [theRequest setHTTPMethod:@"POST"]; [theRequest addValue:@"text/xml" forHTTPHeaderField:@"content-type"]; [theRequest setCachePolicy:NSURLCacheStorageNotAllowed]; [theRequest setTimeoutInterval:5.0]; NSString* pStr = [[NSString alloc] initWithFormat:@"<?xml version=\"1.0\" encoding=\"UTF-8\"?><methodCall><methodName>samurai.SessionInitiate</methodName><params><param><value><struct><member><name>LocalUri</name><value><string></string></value></member><member><name>RemoteUri</name><value><string>sip:%@@sipgate.net</string></value></member><member><name>TOS</name><value><string>text</string></value></member><member><name>Content</name><value><string>%@</string></value></member><member><name>Schedule</name><value><string></string></value></member></struct></value></param></params></methodCall>", modded, TextView.text]; NSData* pBody = [pStr dataUsingEncoding:NSUTF8StringEncoding]; [theRequest setHTTPBody:pBody]; NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self]; if (!theConnection) { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"A Connection could not be established!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles: nil]; [alert show]; [alert release]; sendButton.enabled = TRUE; return; } [pStr release]; [pBody release]; } } The Username and Password have to be in the URL, and it works in most cases, but when the password consists of special characters like in the example "%=&=-Test2009", the Webservice does not respond. If it is something like "Test2009" it works fine. Does anyone have an idea why, and maybe a solution for that?

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• Twitter Bootstrap Collapsible Navbar Duplicating

  - by sixeightzero

  I am working on a project using Twitter Bootstrap. One thing that I noticed is that my pages have duplicate navbars when they are defined as collapsible and the page is resized smaller. Here is the duplicate NavBar: Here is the normal width NavBar: Code: <!DOCTYPE html> <html lang="en"> <!--[if lt IE 7]> <html class="no-js lt-ie9 lt-ie8 lt-ie7"> <![endif]--> <!--[if IE 7]> <html class="no-js lt-ie9 lt-ie8"> <![endif]--> <!--[if IE 8]> <html class="no-js lt-ie9"> <![endif]--> <!--[if gt IE 8]><!--> <html class="no-js"> <!--<![endif]--> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title></title> <meta name="description" content=""> <meta name="viewport" content="width=device-width"> <link rel="stylesheet" href="/assets/css/bootstrap.css"> <style> body { padding-top: 60px; } </style> <link rel="stylesheet" href="/assets/css/bootstrap-responsive.min.css"> <link rel="stylesheet" href="/assets/css/main.css"> <script>window.jQuery || document.write('<script src="/assets/js/vendor/jquery-1.8.1.min.js"><\/script>')</script> <script src="/assets/js/vendor/modernizr-2.6.1-respond-1.1.0.min.js"></script> </head> <body class="dark"> <!--[if lt IE 9]> <p class="chromeframe">You are using an outdated browser. <a href="http://browsehappy.com/">Upgrade your browser today</a> or <a href="http://www.google.com/chromeframe/?redirect=true">install Google Chrome Frame</a> to better experience this site.</p> <![endif]--> <div class="navbar navbar-inverse navbar-fixed-top"> <div class="navbar-inner"> <div class="container"> <a class="btn btn-navbar" data-toggle="collapse" data-target=".nav-collapse"> <span class="icon-bar"></span> <span class="icon-bar"></span> <span class="icon-bar"></span> </a> <a class="brand" href="#">Project name</a> <div class="nav-collapse collapse"> <ul class="nav"> <li class="active"><a href="#">Home</a></li> <li><a href="#about">About</a></li> <li><a href="#contact">Contact</a></li> <li class="dropdown"> <a href="#" class="dropdown-toggle" data-toggle="dropdown">Dropdown <b class="caret"></b></a> <ul class="dropdown-menu"> <li><a href="#">Action</a></li> <li><a href="#">Another action</a></li> <li><a href="#">Something else here</a></li> <li class="divider"></li> <li class="nav-header">Nav header</li> <li><a href="#">Separated link</a></li> <li><a href="#">One more separated link</a></li> </ul> </li> </ul> </div><!--/.nav-collapse --> </div> </div> </div> Has anyone else run into this and have some pointers?

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• How to define generic super type for static factory method?

  - by Esko

  If this has already been asked, please link and close this one. I'm currently prototyping a design for a simplified API of a certain another API that's a lot more complex (and potentially dangerous) to use. Considering the related somewhat complex object creation I decided to use static factory methods to simplify the API and I currently have the following which works as expected: public class Glue<T> { private List<Type<T>> types; private Glue() { types = new ArrayList<Type<T>>(); } private static class Type<T> { private T value; /* some other properties, omitted for simplicity */ public Type(T value) { this.value = value; } } public static <T> Glue<T> glueFactory(String name, T first, T second) { Glue<T> g = new Glue<T>(); Type<T> firstType = new Glue.Type<T>(first); Type<T> secondType = new Glue.Type<T>(second); g.types.add(firstType); g.types.add(secondType); /* omitted complex stuff */ return g; } } As said, this works as intended. When the API user (=another developer) types Glue<Horse> strongGlue = Glue.glueFactory("2HP", new Horse(), new Horse()); he gets exactly what he wanted. What I'm missing is that how do I enforce that Horse - or whatever is put into the factory method - always implements both Serializable and Comparable? Simply adding them to factory method's signature using <T extends Comparable<T> & Serializable> doesn't necessarily enforce this rule in all cases, only when this simplified API is used. That's why I'd like to add them to the class' definition and then modify the factory method accordingly. PS: No horses (and definitely no ponies!) were harmed in writing of this question.

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• Overloading framework methods in objective-c, or retaining local changes with framework updates.

  - by Jeff B

  I am using cocos2d to build an iPhone game. It's mostly done, but along the way I came across some things that I would like to handle better. I am fairly new to Objective C, and honestly I do more Perl scripting in my day-to-day job than anything, so my C skills are a little rusty. One of them is the fact that I have modified cocos2d files for some specific cases in my game. However, when I update to a new version, I have to manually pull my changes forward. So, the question is, what is the best way to deal with this? Some options I have thought of: Overload/redefine the cocos2d classes. I was under the impression that I cannot overload existing class functions, so I don't think this will work. Create patches that I re-apply after library updates. I don't think this will work as the new files won't necessarily be the same as the old ones, and if they were, I could just copy the whole file forward. Turn in my changes to Cocos2d. Not an option as my changes are very specific to my application. Am I missing something obvious? UPDATE: I will explain what I am doing to be more clear. Cocos2d has a CCNode object, which can contain children, etc. I added a shadow, which is very similar to a child, but handled a little differently. The shadow has an offset from the parent, and translates with it's parent, rotates around it's own center when the parent rotates, etc. The shadow is not included as a true child, however, so given the correct z-index, the shadows can render under ALL other objects, but still move with the parent. To do this I added addShadow functions to CCNode, and modified the setPosition and setRotate functions to move the shadowSprite: CCNode.m: -(id) init { if ((self=[super init]) ) { ... shadowSprite_ = nil; ... } } ... -(BOOL) addShadow: (CCNode*) child offset: (CGPoint) offset { shadowSprite_ = child; shadowSprite_.position = CGPointMake(position_.x+offset.x, position_.y+offset.y); return YES; } ... -(void) setRotation: (float)newRotation { rotation_ = newRotation; isTransformDirty_ = isInverseDirty_ = YES; if(shadowSprite_) { [shadowSprite_ setRotation: newRotation]; } } There is more, of course, including the prototypes in the .h file, but that is the basics. I don't think I need shadowSprite to be a property, because I don't need to access it after it has been added.

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• measure rendered html in javascript without affecting the measurement

  - by drawnonward

  I am doing pagination in javascript. This is typographic pagination, not chopping up database results. For the most part it works, but I have run into a heisenberg issue where I cannot quite measure text without affecting it. I am not trying to measure text before it is rendered. I want the actual position it shows up at on screen, so I can paginate to where it is naturally wrapped. I am measuring the vertical position of characters, not the horizontal width of strings. The way I do this is similar to this answer in that I am applying a style to a block of text, then measuring the position of the newly created span. If the span does not reach the end of the page, I clear it and make a new span in a linear search. The problem is that the anti-aliased sub-pixel text layout is different when the span is applied. In rare cases, this causes the text to wrap differently when I measure it. I have only seen this when wrapping at a hyphen, and I assume it would not happen when wrapping at white space. As a concrete example, "prepared-he" is the string I am having trouble with. When I measure up to "prepare" it appears, as expected, to be within the current page. When I measure "prepared" the whole phrase wraps down to the next line, moving it to the next page, so it looks like the "d" is the character to break at. I break the text between "prepare" and "d-he" and that is wrong. Trying to evaluate individual characters opens a whole can of worms I would rather avoid. The wrapping changes because, with the new span, the line is 1 pixel wider. A solution to my problem could either be a better way to measure text using javascript, or a way to wrap text in a new element without affecting layout. I have tried setting margin-right:-1px for the class of the span being created to wrap the text. This had no noticeable effect. I am doing this in a UIWebView on the iPhone. There are some measurement related calls that are available in normal WebKit that are not available here. For example, Range does not have getBoundingClientRect or support setting an offset other than 0 in setStart or setEnd. Thank you

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• Core Data deleteObject: sets attributes to nil

  - by SG1

  I am implementing an undo/redo mechanism in my app. This works fine for lots of cases. However, I can't undo past deleteObject:. the object is correctly saved in the undo queue, and I get it back and reinsterted into the Core Data stack just fine when calling undo. The problem is that all it's attributes are getting set to nil when I delete it. I have an entity "Canvas" with a to-many relationship called "graphics" to a "Graphic" entity, which has its inverse set to "canvas". Deleting a Graphic, then inserting it back, doesn't work. Here's the code (the redo method is basically the same): - (void)deleteGraphic:(id)aGraphic { //NSLog(@"undo drawing"); //Prepare the undo/redo [self.undoManager beginUndoGrouping]; [self.undoManager setActionName:@"Delete Graphic"]; [[self.detailItem valueForKey:@"graphics"] removeObject:aGraphic]; [[self managedObjectContext] deleteObject:aGraphic]; //End undo/redo [self.undoManager registerUndoWithTarget:self selector:@selector(insertGraphic:) object:aGraphic]; [self.undoManager endUndoGrouping]; NSLog(@"graphics are %@", [self sortedGraphics]); //Update drawing [self.quartzView setNeedsDisplay]; } and here's the wierdness: Before delete: graphics are ( <NSManagedObject: 0x1cc3f0> (entity: Graphic; id: 0x1c05f0 <x-coredata:///Graphic/t840FE8AD-F2E7-4214-822F-7994FF93D4754> ; data: { canvas = 0x162b70 <x-coredata://A919979E-75AD-474D-9561-E0E8F3388718/Canvas/p20>; content = <62706c69 73743030 d4010203 04050609 0a582476 65727369 6f6e5424 746f7059 24617263 68697665 7258246f 626a6563 7473>; frameRect = nil; label = nil; order = 1; path = "(...not nil..)"; traits = "(...not nil..)"; type = Path; }) After redo: graphics are ( <NSManagedObject: 0x1cc3f0> (entity: Graphic; id: 0x1c05f0 <x-coredata:///Graphic/t840FE8AD-F2E7-4214-822F-7994FF93D4754> ; data: { canvas = nil; content = nil; frameRect = nil; label = nil; order = 0; path = nil; traits = nil; type = nil; }), You can see it's the same object, just totally bleached by Core Data. The relationship delete rouls apparently have nothing to do with it as I've set them to "No Action" in a test.

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• Checking if an int is prime more efficiently

  - by SipSop

  I recently was part of a small java programming competition at my school. My partner and I have just finished our first pure oop class and most of the questions were out of our league so we settled on this one (and I am paraphrasing somewhat): "given an input integer n return the next int that is prime and its reverse is also prime for example if n = 18 your program should print 31" because 31 and 13 are both prime. Your .class file would then have a test case of all the possible numbers from 1-2,000,000,000 passed to it and it had to return the correct answer within 10 seconds to be considered valid. We found a solution but with larger test cases it would take longer than 10 seconds. I am fairly certain there is a way to move the range of looping from n,..2,000,000,000 down as the likely hood of needing to loop that far when n is a low number is small, but either way we broke the loop when a number is prime under both conditions is found. At first we were looping from 2,..n no matter how large it was then i remembered the rule about only looping to the square root of n. Any suggestions on how to make my program more efficient? I have had no classes dealing with complexity analysis of algorithms. Here is our attempt. public class P3 { public static void main(String[] args){ long loop = 2000000000; long n = Integer.parseInt(args[0]); for(long i = n; i<loop; i++) { String s = i +""; String r = ""; for(int j = s.length()-1; j>=0; j--) r = r + s.charAt(j); if(prime(i) && prime(Long.parseLong(r))) { System.out.println(i); break; } } System.out.println("#"); } public static boolean prime(long p){ for(int i = 2; i<(int)Math.sqrt(p); i++) { if(p%i==0) return false; } return true; } } ps sorry if i did the formatting for code wrong this is my first time posting here. Also the output had to have a '#' after each line thats what the line after the loop is about Thanks for any help you guys offer!!!

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• Performance of looping over an Unboxed array in Haskell

  - by Joey Adams

  First of all, it's great. However, I came across a situation where my benchmarks turned up weird results. I am new to Haskell, and this is first time I've gotten my hands dirty with mutable arrays and Monads. The code below is based on this example. I wrote a generic monadic for function that takes numbers and a step function rather than a range (like forM_ does). I compared using my generic for function (Loop A) against embedding an equivalent recursive function (Loop B). Having Loop A is noticeably faster than having Loop B. Weirder, having both Loop A and B together is faster than having Loop B by itself (but slightly slower than Loop A by itself). Some possible explanations I can think of for the discrepancies. Note that these are just guesses: Something I haven't learned yet about how Haskell extracts results from monadic functions. Loop B faults the array in a less cache efficient manner than Loop A. Why? I made a dumb mistake; Loop A and Loop B are actually different. Note that in all 3 cases of having either or both Loop A and Loop B, the program produces the same output. Here is the code. I tested it with ghc -O2 for.hs using GHC version 6.10.4 . import Control.Monad import Control.Monad.ST import Data.Array.IArray import Data.Array.MArray import Data.Array.ST import Data.Array.Unboxed for :: (Num a, Ord a, Monad m) => a -> a -> (a -> a) -> (a -> m b) -> m () for start end step f = loop start where loop i | i <= end = do f i loop (step i) | otherwise = return () primesToNA :: Int -> UArray Int Bool primesToNA n = runSTUArray $ do a <- newArray (2,n) True :: ST s (STUArray s Int Bool) let sr = floor . (sqrt::Double->Double) . fromIntegral $ n+1 -- Loop A for 4 n (+ 2) $ \j -> writeArray a j False -- Loop B let f i | i <= n = do writeArray a i False f (i+2) | otherwise = return () in f 4 forM_ [3,5..sr] $ \i -> do si <- readArray a i when si $ forM_ [i*i,i*i+i+i..n] $ \j -> writeArray a j False return a primesTo :: Int -> [Int] primesTo n = [i | (i,p) <- assocs . primesToNA $ n, p] main = print $ primesTo 30000000

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• C++0x Overload on reference, versus sole pass-by-value + std::move?

  - by dean

  It seems the main advice concerning C++0x's rvalues is to add move constructors and move operators to your classes, until compilers default-implement them. But waiting is a losing strategy if you use VC10, because automatic generation probably won't be here until VC10 SP1, or in worst case, VC11. Likely, the wait for this will be measured in years. Here lies my problem. Writing all this duplicate code is not fun. And it's unpleasant to look at. But this is a burden well received, for those classes deemed slow. Not so for the hundreds, if not thousands, of smaller classes. ::sighs:: C++0x was supposed to let me write less code, not more! And then I had a thought. Shared by many, I would guess. Why not just pass everything by value? Won't std::move + copy elision make this nearly optimal? Example 1 - Typical Pre-0x constructor OurClass::OurClass(const SomeClass& obj) : obj(obj) {} SomeClass o; OurClass(o); // single copy OurClass(std::move(o)); // single copy OurClass(SomeClass()); // single copy Cons: A wasted copy for rvalues. Example 2 - Recommended C++0x? OurClass::OurClass(const SomeClass& obj) : obj(obj) {} OurClass::OurClass(SomeClass&& obj) : obj(std::move(obj)) {} SomeClass o; OurClass(o); // single copy OurClass(std::move(o)); // zero copies, one move OurClass(SomeClass()); // zero copies, one move Pros: Presumably the fastest. Cons: Lots of code! Example 3 - Pass-by-value + std::move OurClass::OurClass(SomeClass obj) : obj(std::move(obj)) {} SomeClass o; OurClass(o); // single copy, one move OurClass(std::move(o)); // zero copies, two moves OurClass(SomeClass()); // zero copies, one move Pros: No additional code. Cons: A wasted move in cases 1 & 2. Performance will suffer greatly if SomeClass has no move constructor. What do you think? Is this correct? Is the incurred move a generally acceptable loss when compared to the benefit of code reduction?

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• What's wrong with Bundler working with RubyGems to push a Git repo to Heroku?

  - by stanigator

  I've made sure that all the files are in the root of the repository as recommended in this discussion. However, as I follow the instructions in this section of the book, I can't get through the section without the problems. What do you think is happening with my system that's causing the error? I have no clue at the moment of what the problem means despite reading the following in the log. Thanks in advance for your help! stanley@ubuntu:~/rails_sample/first_app$ git push heroku master Warning: Permanently added the RSA host key for IP address '50.19.85.156' to the list of known hosts. Counting objects: 96, done. Compressing objects: 100% (79/79), done. Writing objects: 100% (96/96), 28.81 KiB, done. Total 96 (delta 22), reused 0 (delta 0) -----> Heroku receiving push -----> Ruby/Rails app detected -----> Installing dependencies using Bundler version 1.2.0.pre Running: bundle install --without development:test --path vendor/bundle --binstubs bin/ --deployment Fetching gem metadata from https://rubygems.org/....... Installing rake (0.9.2.2) Installing i18n (0.6.0) Installing multi_json (1.3.5) Installing activesupport (3.2.3) Installing builder (3.0.0) Installing activemodel (3.2.3) Installing erubis (2.7.0) Installing journey (1.0.3) Installing rack (1.4.1) Installing rack-cache (1.2) Installing rack-test (0.6.1) Installing hike (1.2.1) Installing tilt (1.3.3) Installing sprockets (2.1.3) Installing actionpack (3.2.3) Installing mime-types (1.18) Installing polyglot (0.3.3) Installing treetop (1.4.10) Installing mail (2.4.4) Installing actionmailer (3.2.3) Installing arel (3.0.2) Installing tzinfo (0.3.33) Installing activerecord (3.2.3) Installing activeresource (3.2.3) Installing coffee-script-source (1.3.3) Installing execjs (1.3.2) Installing coffee-script (2.2.0) Installing rack-ssl (1.3.2) Installing json (1.7.3) with native extensions Installing rdoc (3.12) Installing thor (0.14.6) Installing railties (3.2.3) Installing coffee-rails (3.2.2) Installing jquery-rails (2.0.2) Using bundler (1.2.0.pre) Installing rails (3.2.3) Installing sass (3.1.18) Installing sass-rails (3.2.5) Installing sqlite3 (1.3.6) with native extensions Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension. /usr/local/bin/ruby extconf.rb checking for sqlite3.h... no sqlite3.h is missing. Try 'port install sqlite3 +universal' or 'yum install sqlite-devel' and check your shared library search path (the location where your sqlite3 shared library is located). *** extconf.rb failed *** Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options. Provided configuration options: --with-opt-dir --without-opt-dir --with-opt-include --without-opt-include=${opt-dir}/include --with-opt-lib --without-opt-lib=${opt-dir}/lib --with-make-prog --without-make-prog --srcdir=. --curdir --ruby=/usr/local/bin/ruby --with-sqlite3-dir --without-sqlite3-dir --with-sqlite3-include --without-sqlite3-include=${sqlite3-dir}/include --with-sqlite3-lib --without-sqlite3-lib=${sqlite3-dir}/lib --enable-local --disable-local Gem files will remain installed in /tmp/build_3tplrxvj7qa81/vendor/bundle/ruby/1.9.1/gems/sqlite3-1.3.6 for inspection. Results logged to /tmp/build_3tplrxvj7qa81/vendor/bundle/ruby/1.9.1/gems/sqlite3-1.3.6/ext/sqlite3/gem_make.out An error occurred while installing sqlite3 (1.3.6), and Bundler cannot continue. Make sure that `gem install sqlite3 -v '1.3.6'` succeeds before bundling. ! ! Failed to install gems via Bundler. ! ! Heroku push rejected, failed to compile Ruby/rails app To [email protected]:growing-mountain-2788.git ! [remote rejected] master -> master (pre-receive hook declined) error: failed to push some refs to '[email protected]:growing-mountain-2788.git' ------Gemfile------------------------ As requested, here's the auto-generated gemfile: source 'https://rubygems.org' gem 'rails', '3.2.3' # Bundle edge Rails instead: # gem 'rails', :git => 'git://github.com/rails/rails.git' gem 'sqlite3' gem 'json' # Gems used only for assets and not required # in production environments by default. group :assets do gem 'sass-rails', '~> 3.2.3' gem 'coffee-rails', '~> 3.2.1' # See https://github.com/sstephenson/execjs#readme for more supported runtimes # gem 'therubyracer', :platform => :ruby gem 'uglifier', '>= 1.0.3' end gem 'jquery-rails' # To use ActiveModel has_secure_password # gem 'bcrypt-ruby', '~> 3.0.0' # To use Jbuilder templates for JSON # gem 'jbuilder' # Use unicorn as the app server # gem 'unicorn' # Deploy with Capistrano # gem 'capistrano' # To use debugger # gem 'ruby-debug'

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• Checking to see if a number is evenly divisible by other numbers with recursion in Python

  - by Ernesto

  At the risk of receiving negative votes, I will preface this by saying this is a midterm problem for a programming class. However, I have already submitted the code and passed the question. I changed the name of the function(s) so that someone can't immediately do a search and find the correct code, as that is not my purpose. I am actually trying to figure out what is actually MORE CORRECT from two pieces that I wrote. The problem tells us that a certain fast food place sells bite-sized pieces of chicken in packs of 6, 9, and 20. It wants us to create a function that will tell if a given number of bite-sized piece of chicken can be obtained by buying different packs. For example, 15 can be bought, because 6 + 9 is 15, but 16 cannot be bought, because no combination of the packs will equal 15. The code I submitted and was "correct" on, was: def isDivisible(n): """ n is an int Returns True if some integer combination of 6, 9 and 20 equals n Otherwise returns False. """ a, b, c = 20, 9, 6 if n == 0: return True elif n < 0: return False elif isDivisible(n - a) or isDivisible(n - b) or isDivisible(n - c): return True else: return False However, I got to thinking, if the initial number is 0, it will return True. Would an initial number of 0 be considered "buying that amount using 6, 9, and/or 20"? I cannot view the test cases the grader used, so I don't know if the grader checked 0 as a test case and decided that True was an acceptable answer or not. I also can't just enter the new code, because it is a midterm. I decided to create a second piece of code that would handle an initial case of 0, and assuming 0 is actually False: def isDivisible(n): """ n is an int Returns True if some integer combination of 6, 9 and 20 equals n Otherwise returns False. """ a, b, c = 20, 9, 6 if n == 0: return False else: def helperDivisible(n): if n == 0: return True elif n < 0: return False elif helperDivisible(n - a) or helperDivisible(n - b) or helperDivisible(n - c): return True else: return False return helperDivisible(n) As you can see, my second function had to use a "helper" function in order to work. My overall question, though, is which function do you think would provide the correct answer, if the grader had tested for 0 as an initial input?

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