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• Help with possible Haskell type inference quiz questions

  - by Linda Cohen

  foldr:: (a -> b -> b) -> b -> [a] -> b map :: (a -> b) -> [a] -> [b] mys :: a -> a (.) :: (a -> b) -> (c -> a) -> c -> b what is inferred type of: a.map mys :: b.mys map :: c.foldr map :: d.foldr map.mys :: I've tried to create mys myself using mys n = n + 2 but the type of that is mys :: Num a => a -> a What's the difference between Num a = a - a and just a - a? Or what does 'Num a =' mean? Is it that mys would only take Num type? So anyways, a) I got [a] - [a] I think because it would just take a list and return it +2'd according to my definition of mys b) (a - b) - [a] - [b] I think because map still needs take both arguments like (*3) and a list then returns [a] which goes to mys and returns [b] c) I'm not sure how to do this 1. d) I'm not sure how to do this 1 either but map.mys means do mys first then map right? Are my answers and thoughts correct? If not, why not? THANKS!

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• IHttpModule not being applied to virtual directory

  - by arthurdent510

  I have a network folder that is mapped to my iis app as a virtual directory and I'm trying to do some authentication for files that are located there with an ihttpmodule. I've verified that the ihttpmodule is firing properly for anything else in my app, just not the files located in virtual directory. Most of what I've found is that the directory can't be listed as an application (which it isn't), and everything should work. The other solution that I found was to add the the module tag to the tag, but that didn't seem to help either. Everything that I've found talks about stopping this from happening. So my question is what could be set that is causing this to not work? Is there a certain execute permission that needs to be set? Any other iis settings that could cause this? It is an mvc app, and this is how my directory structure is laid out: server/app <- my application folder server/app/content/downloads <- downloads is the virtual directory Do I have to add the virtual directory directly under my app directory? Is that part of the problem? I don't have direct control of the server my code is running on, so testing things out is a bit of a pain... so I was looking for some more thoughts before starting to send emails off to my operations people. Thanks!

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• Maintaining a pool of DAO Class instances vs doing new operator

  - by Fazal

  we have been trying to benchmark our application performance in multiple way for sometime now. I always believed that object creation in java using Class.newInstance() was not slow (at least after 1.4 version of java). But we anyways did a test to use newInstance method vs mainitain an object pool of 1000 objects. We did about 200K iterations of loading data from DB using JDBC and populating these objects. I was amazed (even shocked) to see that newInstance code compared to object pool code was almost 10 times slower. These objects represent tables with about 50 fields and all string type. Can someone share there thoughts on this issue as now I am more confused if object pooling of atleast some DAO instances is a better option. The pool size as I see right now should be large enough to meet size of average requests. There is a flip side as my memory footprint will go up but I am beginning to wonder if this kind of idea makes sense atleast for some of the DAO entities representing tables of about 50 or more columns Please share your ideas and let me know if this has been tried by someone or am I missing some point here

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• How to select the first property with unknown name and first item from array in JSON

  - by Oscar Godson

  I actually have two questions, both are probably simple, but for some odd reason I cant figure it out... I've worked with JSON 100s of times before too! but here is the JSON in question: {"69256":{ "streaminfo":{ "stream_ID":"1025", "sourceowner_ID":"2", "sourceowner_avatar":"http:\/\/content.nozzlmedia.com\/images\/sourceowner_avatar2.jpg", "sourceownertype_ID":"1", "stream_name":"Twitter", "streamtype":"Social media" "appsarray":[] }, "item":{ "headline":"Charboy", "main_image":"http:\/\/content.nozzlmedia.com\/images\/author_avatar173212.jpg", "summary":"ate a tomato and avocado for dinner...", "nozzl_captured":"2010-05-12 23:02:12", "geoarray":[{ "state":"OR", "county":"Multnomah", "city":"Portland", "neighborhood":"Downtown", "zip":"97205", "street":"462 SW 11th Ave", "latitude":"45.5219", "longitude":"-122.682" }], "full_content":"ate a tomato and avocado for dinner tonight. such tasty foods. just enjoyable.", "body_text":"ate a tomato and avocado for dinner tonight. such tasty foods. just enjoyable.", "author_name":"Charboy", "author_avatar":"http:\/\/content.nozzlmedia.com\/images\/author_avatar173212.jpg", "fulltext_url":"http:\/\/twitter.com\/charboy\/statuses\/13889868936", "leftovers":{ "twitter_id":"tag:search.twitter.com,2005:13889868936", "date":"2010-05-13T02:59:59Z", "location":"iPhone: 45.521866,-122.682262" }, "wordarray":{ "0":"ate", "1":"tomato", "2":"avocado", "3":"dinner", "4":"tonight", "5":"tasty", "6":"foods", "7":"just", "8":"enjoyable", "9":"Charboy", "11":"Twitter", "13":"state:OR", "14":"county:Multnomah, OR", "15":"city:Portland, OR", "16":"neighborhood:Downtown", "17":"zip:97205" } } } } Question 1: How do I loop through each item (69256) when the number is random? e.g. item 1 is 123, item2 is 646? Like, for example, a normal JSON feed would have something like: {'item':{'blah':'lorem'},'item':{'blah':'ipsum'}} the JS would be like console.log(item.blah) to return lorem then ipsum in a loop How do I do it when i dont know the first item of the object? Question 2: How do I select items from the geoarray object? I tried: json.test.item.geoarray.latitude and json.test.item.geoarray['latitude']

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• R: outlier cleaning for each column in a dataframe by using quantiles 0.05 and 0.95

  - by Rainer

  hi, I am a R-novice. I want to do some outlier cleaning and over-all-scaling from 0 to 1 before putting the sample into a random forest. g<-c(1000,60,50,60,50,40,50,60,70,60,40,70,50,60,50,70,10) If i do a simple scaling from 0 - 1 the result would be: > round((g - min(g))/abs(max(g) - min(g)),1) [1] 1.0 0.1 0.0 0.1 0.0 0.0 0.0 0.1 0.1 0.1 0.0 0.1 0.0 0.1 0.0 0.1 0.0 So my idea is to replace the values of each column that are greater than the 0.95-quantile with the next value smaller than the 0.95-quantile - and the same for the 0.05-quantile. So the pre-scaled result would be: g<-c(**70**,60,50,60,50,40,50,60,70,60,40,70,50,60,50,70,**40**) and scaled: > round((g - min(g))/abs(max(g) - min(g)),1) [1] 1.0 0.7 0.3 0.7 0.3 0.0 0.3 0.7 1.0 0.7 0.0 1.0 0.3 0.7 0.3 1.0 0.0 I need this formula for a whole dataframe, so the functional implementation within R should be something like: > apply(c, 2, function(x) x[x`<quantile(x, 0.95)]`<-max(x[x, ... max without the quantile(x, 0.95)) Can anyone help? Spoken beside: if there exists a function that does this job directly, please let me know. I already checked out cut and cut2. cut fails because of not-unique breaks; cut2 would work, but only gives back string values or the mean value, and I need a numeric vector from 0 - 1. for trial: a<-c(100,6,5,6,5,4,5,6,7,6,4,7,5,6,5,7,1) b<-c(1000,60,50,60,50,40,50,60,70,60,40,70,50,60,50,70,10) c<-cbind(a,b) c<-as.data.frame(c) Regards and thanks for help, Rainer

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• "Exclusive" DirectDraw palette isn't actually exclusive

  - by CyberShadow

  We're maintaining an old video game that uses a full-screen 256-color graphics mode with DirectDraw. The problem is, some applications running in the background sometimes try to change the system palette while the game is running, which results in corrupted graphics. We can (sometimes) detect when this happens by processing the WM_PALETTECHANGED message. A few update versions ago we added logging (just log the window title/class/process name), which helped users identify offending applications and close them. MSN Live Messenger was a common culprit. The problem got worse when we found out that Windows Vista (and 7) does it "by itself". The WM_PALETTECHANGED parameters point towards CSRSS and the desktop window. In Vista, a workaround that often worked was to open any folder (Computer, Documents, etc.) and leave it open while running the game. Sounds ridiculous, but it worked - in most cases. In Windows 7, not even this workaround worked any more. Users found that stopping some services (Windows Update and the indexing service) also resolved the problem on some configurations. Some time ago I just started trying random things in hope of finding a solution. I found that setting the GDI palette (using Create/SelectPalette) before setting the DirectDraw palette (using IDirectDrawPalette::SetEntries) would restore the palette after it became corrupted (WM_PALETTECHANGED handler). SetSystemPaletteUse and calling SetPalette on the primary surface helped some more. However, there is still perceivable flickering when an application tries to steal the palette, which is especially prominent during fades. Question: is there a way to get a "real" exclusive palette, which completely disallows other applications changing the Windows palette as long as our game retains focus?

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• Trying to set up nested while loops using a boolean switch

  - by thorn100

  First time posting. I'm trying to set up a while loop that will ask the user for the employee name, hours worked and hourly wage until the user enters 'DONE'. Eventually I'll modify the code to calculate the weekly pay and write it to a list, but one thing at a time. The problem is once the main while loop executes once, it just stops. Doesn't error out but just stops. I have to kill the program to get it to stop. I want it to ask the three questions again and again until the user is finished. Thoughts? Please note that this is just an exercise and not meant for any real world application. def getName(): """Asks for the employee's full name""" firstName=raw_input("\nWhat is your first name? ") lastName=raw_input("\nWhat is your last name? ") fullName=firstName.title() + " " + lastName.title() return fullName def getHours(): """Asks for the number of hours the employee worked""" hoursWorked=0 while int(hoursWorked)<1 or int(hoursWorked) > 60: hoursWorked=raw_input("\nHow many hours did the employee work: ") if int(hoursWorked)<1 or int(hoursWorked) > 60: print "Please enter an integer between 1 and 60." else: return hoursWorked def getWage(): """Asks for the employee's hourly wage""" wage=0 while float(wage)<6.00 or float(wage)>20.00: wage=raw_input("\nWhat is the employee's hourly wage: ") if float(wage)<6.00 or float(wage)>20.00: print ("Please enter an hourly wage between $6.00 and $20.00") else: return wage ##sentry variables employeeName="" employeeHours=0 employeeWage=0 booleanDone=False #Enter employee info print "Please enter payroll information for an employee or enter 'DONE' to quit." while booleanDone==False: while employeeName=="": employeeName=getName() if employeeName.lower()=="done": booleanDone=True break print "The employee's name is", employeeName while employeeHours==0: employeeHours=getHours() if employeeHours.lower()=="done": booleanDone=True break print employeeName, "worked", employeeHours, "this week." while employeeWage==0: employeeWage=getWage() if employeeWage.lower()=="done": booleanDone=True break print employeeName + "'s hourly wage is $" + employeeWage

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• C#: Is it possible to use expressions or functions as keys in a dictionary?

  - by Svish

  Would it work to use Expression<Func<T>> or Func<T> as keys in a dictionary? For example to cache the result of heavy calculations. For example, changing my very basic cache from a different question of mine a bit: public static class Cache<T> { // Alternatively using Expression<Func<T>> instead private static Dictionary<Func<T>, T> cache; static Cache() { cache = new Dictionary<Func<T>, T>(); } public static T GetResult(Func<T> f) { if (cache.ContainsKey(f)) return cache[f]; return cache[f] = f(); } } Would this even work? Edit: After a quick test, it seems like it actually works. But I discovered that it could probably be more generic, since it would now be one cache per return type... not sure how to change it so that wouldn't happen though... hmm Edit 2: Noo, wait... it actually doesn't. Well, for regular methods it does. But not for lambdas. They get various random method names even if they look the same. Oh well c",)

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• Maximizing the number of true concurrent / parrallel http requests in Silverlight

  - by Clems

  Hi all. I'm using SL 4 beta and my app needs to do a lot of small http requests to the server. I believe that when exceeding the number of allowed concurrent requests, the subsequent requests are put in a queue. I am also aware that SL 4 has both a http browser stack and a http client stack, with both different limit in terms of the number of concurrent requests. Let's say call those limits MAX_BROWSER and MAX_CLIENT. Also I think I read somewhere that the number of concurrent requests is limited per domain, not overall. But I'm sure if this applies to both the http client stack. That means that you CAN have MAX_BROWSER requests to domain1.com AND MAX_BROWSER requests to domain2.com at the same time. And I even believe that sub domains are considered different so you can also have MAX_BROWSER requests to domain1.com AND MAX_BROWSER requests to sub.domain1.com at the same time. I have ownership of the services and domain names so I could easily setup sub domains for my services. Given those considerations I'm trying to optimize the number of concurrent http requests to my server. Here are few questions ? Is is possible to use both stack at the same time ? Is the subdomain/domain story true for both stacks ? None ? If so that would mean that I could potentially have a number of concurrent requests equal to : (MAX_BROWSER + MAX_CLIENT) * NUMBER_OF_DOMAINS which would be fairly good. Is this correct ? I'm kind of sharing my morning thoughts here, hoping somebody has experimented with those things. Thank you.

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• NSUndoManager, Core Data and selective undo/redo

  - by Combat

  I'm working on a core data application that has a rather large hierarchy of managed objects similar to a tree. When a base object is created, it creates a few child objects which in turn create their own child objects and so on. Each of these child objects may gather information using NSURLConnections. Now, I'd like to support undo/redo with the undoManager in the managedObjectContext. The problem is, if a user creates a base object, then tries to undo that action, the base object is not removed. Instead, one or more of the child objects may be removed. Obviously this type of action is unpredictable and unwanted. So I tried disabling undo registration by default. I did this by calling disableUndoRegistration: before anything is modified in the managedObjectContext. Then, enabling undo registration before base operations such as creating a base object the again re-disabling registrations afterwords. Now when i try to undo, I get this error: undo: NSUndoManager 0x1026428b0 is in invalid state, undo was called with too many nested undo groups Thoughts?

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• Foosball result prediction

  - by Wolf

  In our office, we regularly enjoy some rounds of foosball / table football after work. I have put together a small java program that generates random 2vs2 lineups from the available players and stores the match results in a database afterwards. The current prediction of the outcome uses a simple average of all previous match results from the 4 involved players. This gives a very rough estimation, but I'd like to replace it with something more sophisticated, taking into account things like: players may be good playing as attacker but bad as defender (or vice versa) players do well against a specific opponent / bad against others some teams work well together, others don't skills change over time What would be the best algorithm to predict the game outcome as accurately as possible? Someone suggested using a neural network for this, which sounds quite interesting... but I do not have enough knowledge on the topic to say if that could work, and I also suspect it might take too many games to be reasonably trained. EDIT: Had to take a longer break from this due to some project deadlines. To make the question more specific: Given the following mysql table containing all matches played so far: table match_result match_id int pk match_start datetime duration int (match length in seconds) blue_defense int fk to table player blue_attack int fk to table player red_defense int fk to table player red_attack int fk to table player score_blue int score_red int How would you write a function predictResult(blueDef, blueAtk, redDef, redAtk) {...} to estimate the outcome as closely as possible, executing any sql, doing calculations or using external libraries?

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• How can I force PHP's fopen() to return the current version of a web page?

  - by Edward Tanguay

  The current content of this google docs page is: However, when reading this page with the following PHP fopen() script, I get an older, cached version: I've tried two solutions proposed in this question (a random attribute and using POST) and I also tried clearstatcache() but I always get the cached version of the web page. What do I have to change in the following script so that fopen() returns the current version of the web page? <?php $url = 'http://docs.google.com/View?id=dc7gj86r_32g68627ff&amp;rand=' . getRandomDigits(10); echo $url . '<hr/>'; echo loadFile($url); function loadFile($sFilename) { clearstatcache(); if (floatval(phpversion()) >= 4.3) { $sData = file_get_contents($sFilename); } else { if (!file_exists($sFilename)) return -3; $opts = array('http' => array( 'method' => 'POST', 'content'=>'' ) ); $context = stream_context_create($opts); $rHandle = fopen($sFilename, 'r'); if (!$rHandle) return -2; $sData = ''; while(!feof($rHandle)) $sData .= fread($rHandle, filesize($sFilename)); fclose($rHandle); } return $sData; } function getRandomDigits($numberOfDigits) { $r = ""; for($i=1; $i<=$numberOfDigits; $i++) { $nr=rand(0,9); $r .= $nr; } return $r; } ?>

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• Error Converting PIL B&W images to Numpy Arrays

  - by Elliot

  I am getting weird errors when I try to convert a black and white PIL image to a numpy array. An example of the code I am working with is below. if image.mode != '1': image = image.convert('1') #convert to B&W data = np.array(image) #convert data to a numpy array n_lines = data.shape[0] #number of raster passes line_range = range(data.shape[1]) for l in range(n_lines): # process one horizontal line of the image line = data[l] for n in line_range: if line[n] == 1: write_line_to(xl, z+scale*n, speed) #conversion to other program code elif line[n] == 0: run_to(xl, z+scale*n) #conversion to other program code I have tried this using both array and asarray for the conversion, and gotten different errors. If I use array, then the data I get out is nothing like what I put in. It looks like several very shrunken partial images side by side, with the remainder of the image space filled in in black. If I use asarray, then the entirety of python crashes during the raster step (on a random line). If I work with a greyscale image ('L'), then neither of these errors occurs for either array or asarray. Does anyone know what I am doing wrong? Is there something odd about the way PIL encodes B&W images, or something special I need to pass numpy to make it convert properly?

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• Can the Singleton be replaced by Factory?

  - by lostiniceland

  Hello Everyone There are already quite some posts about the Singleton-Pattern around, but I would like to start another one on this topic since I would like to know if the Factory-Pattern would be the right approach to remove this "anti-pattern". In the past I used the singleton quite a lot, also did my fellow collegues since it is so easy to use. For example, the Eclipse IDE or better its workbench-model makes heavy usage of singletons as well. It was due to some posts about E4 (the next big Eclipse version) that made me start to rethink the singleton. The bottom line was that due to this singletons the dependecies in Eclipse 3.x are tightly coupled. Lets assume I want to get rid of all singletons completely and instead use factories. My thoughts were as follows: hide complexity less coupling I have control over how many instances are created (just store the reference I a private field of the factory) mock the factory for testing (with Dependency Injection) when it is behind an interface In some cases the factories can make more than one singleton obsolete (depending on business logic/component composition) Does this make sense? If not, please give good reasons for why you think so. An alternative solution is also appreciated. Thanks Marc

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• Customize jQuery.aptags plugin - mouseclick submit from .ac_results list

  - by atmorell

  Hello, I am using jquery.autocomplete.js and jquery.apitags to select a few elements from a div (.ac_results) This works great, and I can select multiple elements etc. However the jquery-aptags plugin does only fire when enter is pressed. This might confuse some users if they use the mouse to click instead of the arrows/enter on the keyboard. I think this is the code inside jquery.aptags that submits the tag. // // Hook to the keypress event. // $(this).bind('keypress', { __c: __c }, function (e) { var c = ''; var i = 0; var v = $(this).val(); if (e.keyCode == 13) { e.stopPropagation(); e.preventDefault(); __createSpans(this, v, e.data.__c, true); } }); I am wondering if it is possible to call the method directly from a new event. $('.ac_results > ul > li').livequery(function() { $(this).bind('click', function() { $('#address_city'). //how do I fire the "enter" event from here? }); }); Any thoughts?

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• Advanced ASP.NET Gridview Layout

  - by chief7

  So i had a feature request to add fields to a second table row for a single data row on a GridView. At first, I looked at extending the functionality of the GridView but soon realized this would be a huge task and since I consider this request a shim for a larger future feature decided against it. Also want to move to MVC in the near future and this would be throw away code. So instead I created a little jquery script to move the cell to the next row in the table. $(document).ready(function() { $(".fieldAttributesNextRow").each(function() { var parent = $(this).parent(); var newRow = $("<tr></tr>"); newRow.attr("class", $(parent).attr("class")); var headerRow = $(parent).parent().find(":first"); var cellCount = headerRow.children().length - headerRow.children().find(".hide").length; newRow.append($(this).attr("colspan", cellCount)); $(parent).after(newRow); }) }); What do you think of this? Is this a poor design decision? I am actually quite pleased with the ease of this solution. Please provide your thoughts.

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• widget within module in Yii

  - by Karolis

  I'm trying to create a widget within the module and then load that widget from 'outside' of the module. More particularly I'm using user module written by someone else. I don't want to have a separate page for displaying a login form, therefore I tried to make a CPortlet/widget (confusion) displaying the login form. Basically, I've moved the code from LoginController into that widget. Then I try to display the widget on some random page by <?php $this->widget('user.components.LoginForm'); ?> However, I get an error CWebApplication does not have a method named "encrypting". in UserIdentity class in this line: else if(Yii::app()->controller->module->encrypting($this->password)!==$user->password) This happens, because I'm basically trying to execute this code within context of the app and not the module. Thus the "Yii::app()-controller-module" trick doesn't really work as expected. What am I doing wrong:-\ Is there a better way to achieve this. I.e. display that login form in some other page, which is normally displayed by accessing login controller within user module (user/login) or is a widget the right way of doing it? Thanks.

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• Uninterruptible Windows Process

  - by Nullstr1ng

  Hi Guys, We're starting a new custom project right now from a client and one of the requirements is the process cannot be terminated unless the system is shutting down, restarting, or logging-off. This application monitors the USB interface. We will be using WMI to query the device periodically. The client want's to run the application on Windows XP Operating System and doesn't like installing .NET. So we targeted Visual Basic 6 as our language. My main concern is this application cannot be terminated. Our Project Adviser talks about Anti-virus and yes, some of the anti virus cannot be terminated. I was thinking how to do the same in Visual Basic 6. I know there will be API involved on the project but where should I go? so API is ok with me. I saw some articles that converts the EXE to a SERVICE, create Windows Service in Visual Basic 6, etc. So please .. share your thoughts.

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• Strange behaviour with GregorianCalendar

  - by Spark

  I just encountered a strange behaviour with the GregorianCalendar class, and I was wondering if I really was doing something bad. This only appends when the initialization date's month has an actualMaximum bigger than the month I'm going to set the calendar to. Here is the example code : // today is 2010/05/31 GregorianCalendar cal = new GregorianCalendar(); cal.set(Calendar.YEAR, 2010); cal.set(Calendar.MONTH, 1); // FEBRUARY cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH)); cal.set(Calendar.HOUR_OF_DAY, cal.getActualMaximum(Calendar.HOUR_OF_DAY)); cal.set(Calendar.MINUTE, cal.getActualMaximum(Calendar.MINUTE)); cal.set(Calendar.SECOND, cal.getActualMaximum(Calendar.SECOND)); cal.set(Calendar.MILLISECOND, cal.getActualMaximum(Calendar.MILLISECOND)); return cal.getTime(); // => 2010/03/03, wtf I know the problem is caused by the fact that the calendar initialization date is a 31 day month ( may ), which mess with the month set to february (28 days). The fix is easy ( just set day_of_month to 1 before setting year and month ), but I was wondering is this really was the wanted behaviour. Any thoughts ?

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• Using JQuery with dynamically added controls (MVC)

  - by Mario

  I have a set of radio buttons that are dynamically generated (via JSON call): StringBuilder sbEligAll = new StringBuilder(); sbEligAll.Append("<div id='currentselectiondepartment'>"); sbEligAll.Append(" <input type='radio' name='selectalldepartment' id='radCurrent' value='0' /><label for='radCurrent'>Current</label>"); sbEligAll.Append(" <input type='radio' name='selectalldepartment' id='radFuture' value='1' /><label for='radFuture'>Future</label>"); sbEligAll.Append(" <input type='radio' name='selectalldepartment' id='radCurrentAll' value='2' /><label for='radCurrentAll'>Current All</label>"); sbEligAll.Append(" <input type='radio' name='selectalldepartment' id='radFutureAll' value='3' /><label for='radFutureAll'>Future All</label>"); sbEligAll.Append("</div>"); Then: return Json(new { TableList = sbElig.ToString() }, JsonRequestBehavior.AllowGet); Is there a way to get jQuery to be able to interact with these? For example: $("input[name=selectalldepartment]").change(function() { var str = $('input[name=selectalldepartment]:checked').val(); $(".radiolist[value='" + str + "']").attr("checked", true); }); I've tried everything I know how to do, but the jQuery just doesnt fire. (I've added alerts to the jQuery code to see if it actually gets called, and it does not). Any thoughts?! Thanks!

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• Python - Why use anything other than uuid4() for unique strings?

  - by orokusaki

  I see quit a few implementations of unique string generation for things like uploaded image names, session IDs, et al, and many of them employ the usage of hashes like SHA1, or others. I'm not questioning the legitimacy of using custom methods like this, but rather just the reason. If I want a unique string, I just say this: >>> import uuid >>> uuid.uuid4() 07033084-5cfd-4812-90a4-e4d24ffb6e3d And I'm done with it. I wasn't very trusting before I read up on uuid, so I did this: >>> import uuid >>> s = set() >>> for i in range(5000000): # That's 5 million! >>> s.add(uuid.uuid4()) ... ... >>> len(s) 5000000 Not one repeater (I didn't expect one considering the odds are like 1.108e+50, but it's comforting to see it in action). You could even half the odds by just making your string by combining 2 uuid4()s. So, with that said, why do people spend time on random() and other stuff for unique strings, etc? Is there an important security issue or other regarding uuid?

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• Java Client .class File Protection

  - by Zac

  I am in the requirements phase of building a JEE application that will most likely run on a GlassFish/JBoss backend (doesn't matter for now). I know I shouldn't be thinking about architecture at requirements time, but one can't help but start to imagine how the components would all snap together :-) Here are some hard, non-flexible requirements on the client-side: (1) The client application will be a Swing box (2) The client is free to download, but will use a subscription model (thus requiring a login mechanism with server-side authentication/authorization, etc.) (3) Yes, Java is the best platform solution for the problem at hand for reasons outside the scope of this post (4) The client-side .class files need safeguarding against decompiling That last (4th) requirement is the basis of this post. I'm not really worried about someone actually decompiling and getting at my source code: in the end, it's just Swing controls driven by some lightweight business logic. I'm worried about a scenario where someone decompiles my code, modifies it to exploit/attack the server, re-compiles, and fires it up. I've envisioned all sorts of nasty solutions, but didn't know if this was a common problem with a common solution for JEE developers. Any thoughts? Not interested in "code obfuscation" techniques! Thanks for any input!

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• A couple of questions about NHibernate's GuidCombGenerator

  - by Eyvind

  The following code can be found in the NHibernate.Id.GuidCombGenerator class. The algorithm creates sequential (comb) guids based on combining a "random" guid with a DateTime. I have a couple of questions related to the lines that I have marked with *1) and *2) below: private Guid GenerateComb() { byte[] guidArray = Guid.NewGuid().ToByteArray(); // *1) DateTime baseDate = new DateTime(1900, 1, 1); DateTime now = DateTime.Now; // Get the days and milliseconds which will be used to build the byte string TimeSpan days = new TimeSpan(now.Ticks - baseDate.Ticks); TimeSpan msecs = now.TimeOfDay; // *2) // Convert to a byte array // Note that SQL Server is accurate to 1/300th of a millisecond so we divide by 3.333333 byte[] daysArray = BitConverter.GetBytes(days.Days); byte[] msecsArray = BitConverter.GetBytes((long) (msecs.TotalMilliseconds / 3.333333)); // Reverse the bytes to match SQL Servers ordering Array.Reverse(daysArray); Array.Reverse(msecsArray); // Copy the bytes into the guid Array.Copy(daysArray, daysArray.Length - 2, guidArray, guidArray.Length - 6, 2); Array.Copy(msecsArray, msecsArray.Length - 4, guidArray, guidArray.Length - 4, 4); return new Guid(guidArray); } First of all, for *1), wouldn't it be better to have a more recent date as the baseDate, e.g. 2000-01-01, so as to make room for more values in the future? Regarding *2), why would we care about the accuracy for DateTimes in SQL Server, when we only are interested in the bytes of the datetime anyway, and never intend to store the value in an SQL Server datetime field? Wouldn't it be better to use all the accuracy available from DateTime.Now?

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• Creating a Hello World library function in assembly and calling it from C#

  - by Filip Ekberg

  Let's say we use NASM as they do in this answer: how to write hellow world in assembly under windows. I got a couple of thoughts and questions regarding assembly combined with c# or any other .net languages for that matter. First of all I want to be able to create a library that has the following function HelloWorld that takes this parameter: Name In C# the method signature would looke like this: void HelloWorld(string name) and it would print out something like Hello World from name I've searched around a bit but can't find that much good and clean material for this to get me started. I know some basic assembly from before mostly gasthough. So any pointers in the right direction is very much apprechiated. To sum it up Create a function in ASM ( NASM ) that takes one or more parameters Compile and create a library of the above functionality Include the library in any .net language Call the included library function Bonus features How does one handle returned values? Is it possible to write the ASM-method inline? When creating libraries in assembly or c, you do follow a certain "pre defined" way, the c calling convetion, correct?

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• Using Facebook Login to create a user?

  - by andbeyond

  I've read this SO post which led me to this FB policy page, which seemed to include some pertinent information, but I'd like more of a community response, maybe some experienced FB API people who know the limits. My question is if I can use Facebook's Login api to, essentially, create a new user on my website. I really would just like to allow users to easily "transfer" some data from FB in order to more easily create a new account on my site. I realize, first and foremost, that I would obviously announce to the user that by click "submit" in the form, that they are creating a separate account on my site. Pertinent blocks on the policy page state: You may cache data you receive through use of the Facebook API in order to improve your application’s user experience, but you should try to keep the data up to date. This permission does not give you any rights to such data. Which doesn't look good for me, but also this: If you stop using Platform or we disable your application, you must delete all data you have received through use of the Facebook API unless: (a) it is basic account information; or (b) you have received explicit consent from the user to retain their data. Which, in my case, I would be satisfying part B. I would be asking the user's permission to retain the data, as I am simply using Facebook as a conveience to the user when creating an account. I also realize that Facebook has a registration API, but this would require a Facebook styled login form, along with my own sites login form, and I'd rather one interface, as this makes it easier for me on the front and back end. Any thoughts?

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