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• Will a Ph. D. in Computer Science help?

  - by Francisco Garcia

  I am close to my 30s and still learning about programming and software engineering. Like most people who like their profession I truly believe that I should aim to improve and keep updated. One of the things I do is reading technical papers from professional publications (IEEE and ACM) but I admit there are very good bloggers out there too. Lately I started to think (should I say realize?) that Ph. D people actually are expected to expand constantly their knowledge, but little is expected from lower classes once they know enough This made me think that maybe having a Ph. D will help to have more... respect? but I also believe that I am already getting old for that. Futhermore I see many master and doctor programs that does not seem to add any value over hard experience and self learning. I belive that a degree in computer science, althought not necessary, can lay out a good base for programming work. However: What can a Ph. D. degree give you that you cannot learn on your own? (if you are not into something VERY specific and want to work in a non academic environment)

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• JQuery modal box form validation

  - by vikitor

  Hi, I was using a view to create an object for my specific project, but now I have to adapt this to another requirements, such as the creation of this object must be integrated in the creation of another one. The thing is, that this object must be created before starting to create the other one, and the way of doing it will be poping up a modal dialog box with JQuery with the form to create it. I've got to adapt the creation and it works fine, except for the validation messages. It is made in the controller like : if (not.NotName.Trim().Length == 0) { ModelState.AddModelError("NotName", "Name is required"); } if (_notification.checkIfExists(not.NotName, not.NotRecID)) { ModelState.AddModelError("NotName", "Notification already exists"); } And before with a normal view it worked fine, but now I'm not able to get the validation messages as I did. How can you get this validation messages thrown by the controller in the Modal Box? Because now when I made a mistake on purpose in the form in order to get the error it doesn't appear. I've seen the error is displayed in the site, because I've seen it on firebug, but it doesn't appear in my model box. How can I retrieve this errors? Do you know any tutorial that could help me with this? Thank you

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• C# wrapper for objects

  - by Haggai

  I'm looking for a way to create a generic wrapper for any object. The wrapper object will behave just like the class it wraps, but will be able to have more properties, variable, methods etc., for e.g. object counting, caching etc. Say the wrapper class be called Wrapper, and the class to be wrapped be called Square and has the constructor Square(double edge_len) and the properties/methods EdgeLength and Area, I would like to use it as follows: Wrapper<Square> mySquare = new Wrapper<Square>(2.5); /* or */ new Square(2.5); Console.Write("Edge {0} -> Area {1}", mySquare.EdgeLength, mySquare.Area); Obviously I can create such a wrapper class for each class I want to wrap, but I'm looking for a general solution, i.e. Wrapper<T> which can handle both primitive and compound types (although in my current situation I would be happy with just wrapping my own classes). Suggestions? Thanks.

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• Nhibernate + Gridview + TargetInvocationException

  - by Scott

  For our grid views, we're setting the data sources as a list of results from an Nhibernate query. We're using lazy loading, so the objects are actually proxied... most of the time. In some instances the list will consist of types of Student and Composition_Aop_Proxy_jklasjdkl31231, which implements the same members as the Student class. We've still got the session open, so the lazy loading would resolve fine, if GridView didn't throw an error about the different types in the gridview. Our current workaround is to clone the object, which results in fetching all of the data that can be lazily loaded, even though most of it won't be accessed.. ever. This, however, converts the proxy into an actual object and the grid view is happy. The performance implications kind of scare me as we're getting closer to rolling the code out as is. I've tried evicting the object after a save, which should ensure that everything is a proxy, but this doesn't seem like a good idea either. Does anyone have any suggestions/workarounds?

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• Strongly typed dynamic Linq sorting

  - by David

  I'm trying to build some code for dynamically sorting a Linq IQueryable<. The obvious way is here, which sorts a list using a string for the field name http://dvanderboom.wordpress.com/2008/12/19/dynamically-composing-linq-orderby-clauses/ However I want one change - compile time checking of field names, and the ability to use refactoring/Find All References to support later maintenance. That means I want to define the fields as f=f.Name, instead of as strings. For my specific use I want to encapsulate some code that would decide which of a list of named "OrderBy" expressions should be used based on user input, without writing different code every time. Here is the gist of what I've written: var list = from m Movies select m; // Get our list var sorter = list.GetSorter(...); // Pass in some global user settings object sorter.AddSort("NAME", m=m.Name); sorter.AddSort("YEAR", m=m.Year).ThenBy(m=m.Year); list = sorter.GetSortedList(); ... public class Sorter ... public static Sorter GetSorter(this IQueryable source, ...) The GetSortedList function determines which of the named sorts to use, which results in a List object, where each FieldData contains the MethodInfo and Type values of the fields passed in AddSort: public SorterItem AddSort(Func field) { MethodInfo ... = field.Method; Type ... = TypeOf(TKey); // Create item, add item to diction, add fields to item's List // The item has the ThenBy method, which just adds another field to the List } I'm not sure if there is a way to store the entire field object in a way that would allow it be returned later (it would be impossible to cast, since it is a generic type) Is there a way I could adapt the sample code, or come up with entirely new code, in order to sort using strongly typed field names after they have been stored in some container and retrieved (losing any generic type casting)

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• Java and Jasper

  - by bhargava

  Hey Guys, I have integrated Jasper Reports on my netbeans platform and i am able to generate reports using the following code. Map<String, Object> params = new HashMap<String, Object>(); Connection conn = DriverManager.getConnection("databaseUrl", "userid","password"); JasperReport jasperReport = JasperCompileManager.compileReport(reportSource); JasperPrint jasperPrint = JasperFillManager.fillReport(jasperReport, params, conn); JasperExportManager.exportReportToHtmlFile(jasperPrint, reportDest); JasperViewer.viewReport(jasperPrint); This stuff works perfect. But not i am trying to integrate Jasper with GWT.I have my server as glass fish server. I am getting the Connection object using the followind code. public static Connection getConnection() { try { String JNDI = "JNDI name"; InitialContext initCtx = new InitialContext(); javax.sql.DataSource ds = (javax.sql.DataSource) initCtx.lookup(JNDI); Connection conn = (Connection) ds.getConnection(); return conn; } catch (Exception ex) { ex.printStackTrace(); } return null; } and then Map params = new HashMap(); JasperReport jasperReport = JasperCompileManager.compileReport(reportSource); JasperPrint jasperPrint = JasperFillManager.fillReport(jasperReport, params, getConnection()); JasperExportManager.exportReportToHtmlFile(jasperPrint, reportDest); JasperViewer.viewReport(jasperPrint); but i always get Error.I am implementing this on Server.I am having RPC calls to get this method to work when a button is clicked. Can you please help me how to work on this.(That is to integrate Jasper reports with GWT). I would highly appreciate any explanation with some code as i am just a beginner. Thanks

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• IE7 & 8 not fireing jQuery click events for elements appended inside a table

  - by Keith

  I have an IE bug that I'm not sure how to fix. Using jQuery I'm dynamically moving a menu to appear on an element on mouseover. My code (simplified) looks something like this: $j = jQuery.noConflict(); $j(document).ready(function() { //do something on the menu clicks $j('div.ico').click(function() { alert($j(this).parent().html()); }); setUpActions('#tableId', '#menuId'); }); //on mouseover set up the actions menu to appear on mouseover function setUpActions(tableSelector, menuSelector) { $j(tableSelector + ' div.test').mouseover(function() { //note that append will move the underlying //DOM element with all events from it's old //parent to the end of this one. $j(this).append($j(menuSelector).show()); }); } This menu doesn't seem to register events correctly for the menu after it's been moved in IE7, IE8 and IE8-as-IE7 (yeah MS, that's really a 'new rendering engine' in IE8, we all believe you). It works as expected in everything else. You can see the behaviour in a basic demo here. In the demo you can see two examples of the issue: The image behind the buttons should change on hover (done with a CSS :hover selector). It works on the first mouseover but then persists. The click event doesn’t fire – however with the dev tools you can manually call it and it is still subscribed. You can see (2) in IE8's dev tools: Open page in IE8 Open dev tools Select "Script" tab and "Console" sub-tab Type: $j('#testFloat div.ico:first').click() to manually call any subscribed events There will be an alert on the page This means that I'm not losing the event subscriptions, they're still there, IE's just not calling them when I click. Does anyone know why this bug occurs (other than just because of IE's venerable engine)? Is there a workaround? Could it be something that I'm doing wrong that just happens to work as expected in everything else?

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• Flash - can't access classes in another SWF

  - by Ashley Muller

  Hi, I'm trying to load a local SWF file and use the classes in that SWF (its a code only SWF, nothing in library). Here's the code that loads the library: var AD:ApplicationDomain = ApplicationDomain.currentDomain; var context:LoaderContext = new LoaderContext(false, AD); SA_gamecore_loader = new Loader(); SA_gamecore_loader.contentLoaderInfo.addEventListener(Event.COMPLETE, onGameCoreLibraryDataComplete); SA_gamecore_loader.load(new URLRequest("GameCore.swf"), context); Here's the code that tries to instantiate a class from GameCore.swf: var test:Class = GetClassFromDefinition("MenuArt") as Class; var testInstance:Object = new test(); public function GetClassFromDefinition(theStr:String):Object { var theClass:Object; try { theClass = GameCoreLibraryData.applicationDomain.getDefinition(theStr); } catch(e:ReferenceError) { trace(e); return null; } return theClass; } And this is the message that's traced: ReferenceError: Error #1065: Variable MenuArt is not defined. The GameCore.swf is in the same location as the parent swf. I'm using Flash Develop if that helps. Anyone able to point out what I'm doing wrong?

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• SIlverlight Navigate: how does it work? How would you implement in f# w/o VS wizards and helpers?

  - by akaphenom

  After a nights sleep the problem can be stated more accurately as I have a 100% f# / silverlight implementation and am looking to use the built in Navigation components. C# creates page.xaml and page.xaml.cs um - ok; but what is the relationship at a fundamental level? How would I go about doing this in f#? The applcuation is loaded in the default module, and I pull the XAML in and reference it from the application object. Do I need to create instances / references to the pages from within the application object? Or set up some other page management object with the proper name value pairs? When all the Help of VS is stripped away - what are we left with? original post (for those who may be reading replies) I have a 100% silverlight 3.0 / f# 2.0 application I am wrapping my brain around. I have the base application loading correctly - and now I want to add the naigation controls to it. My page is stored as an embedded resource - but the Frame.Navigate takes a URI. I know what I have is wrong but here it is: let nav : Frame = mainGrid ? mainFrame let url = "/page1.xaml" let uri = new System.Uri(url, System.UriKind.Relative) ; nav.Navigate uri Any thoughts?

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

  - by Matt

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

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• Replacing text with apostrophe text via sed in applescript

  - by bob stinton

  I have an applescript to find and replace a number of strings. I ran in the problem of having a replacement string which contained & some time ago, but could get around it by putting \& in the replacement property list. However an apostrophe seems to be far more annoying. Using a single apostrophe just gets ignored (replacement doesn't contain it), using \' gives a syntax error (Expected “"” but found unknown token.) and using \' gets ignored again. (You can keep doing that btw, even number gets ignored uneven gets syntax error) I tried replacing the apostrophe in the actual sed command with double quotes (sed "s…" instead of sed 's…'), which works in the command line, but gives a syntax error in the script (Expected end of line, etc. but found identifier.) The single quotes mess with the shell, the double quotes with applescript. I also tried '\'' as was suggested here and '"'"' from here. Basic script to get the type of errors: set findList to "Thats.nice" set replaceList to "That's nice" set fileName to "Thats.nice.whatever" set resultFile to do shell script "echo " & fileName & " | sed 's/" & findList & "/" & replaceList & " /'"

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• Can somebody explain this remark in the MSDN CreateMutex() documentation about the bInitialOwner fla

  - by Tom Williams

  The MSDN CreatMutex() documentation (http://msdn.microsoft.com/en-us/library/ms682411%28VS.85%29.aspx) contains the following remark near the end: Two or more processes can call CreateMutex to create the same named mutex. The first process actually creates the mutex, and subsequent processes with sufficient access rights simply open a handle to the existing mutex. This enables multiple processes to get handles of the same mutex, while relieving the user of the responsibility of ensuring that the creating process is started first. When using this technique, you should set the bInitialOwner flag to FALSE; otherwise, it can be difficult to be certain which process has initial ownership. Can somebody explain the problem with using bInitialOwner = TRUE? Earlier in the same documentation it suggests a call to GetLastError() will allow you to determine whether a call to CreateMutext() created the mutex or just returned a new handle to an existing mutex: Return Value If the function succeeds, the return value is a handle to the newly created mutex object. If the function fails, the return value is NULL. To get extended error information, call GetLastError. If the mutex is a named mutex and the object existed before this function call, the return value is a handle to the existing object, GetLastError returns ERROR_ALREADY_EXISTS, bInitialOwner is ignored, and the calling thread is not granted ownership. However, if the caller has limited access rights, the function will fail with ERROR_ACCESS_DENIED and the caller should use the OpenMutex function.

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• How can I prevent double file uploading with Amazon S3?

  - by Tony

  I decided to use Amazon S3 for document storage for an app I am creating. One issue I run into is while I need to upload the files to S3, I need to create a document object in my app so my users can perform CRUD actions. One solution is to allow for a double upload. A user uploads a document to the server my Rails app lives on. I validate and create the object, then pass it on to S3. One issue with this is progress indicators become more complicated. Using most out-of-the-box plugins would show the client that file has finished uploading because it is on my server, but then there would be a decent delay when the file was going from my server to S3. This also introduces unnecessary bandwidth (at least it does not seem necessary) The other solution I am thinking about is to upload the file directly to S3 with one AJAX request, and when that is successful, make a second AJAX request to store the object in my database. One issue here is that I would have to validate the file after it is uploaded which means I have to run some clean up code in S3 if the validation fails. Both seem equally messy. Does anyone have something more elegant working that they would not mind sharing? I would imagine this is a common situation with "cloud storage" being quite popular today. Maybe I am looking at this wrong.

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• Writing functions of tuples conveniently in Scala

  - by Alexey Romanov

  Quite a few functions on Map take a function on a key-value tuple as the argument. E.g. def foreach(f: ((A, B)) ? Unit): Unit. So I looked for a short way to write an argument to foreach: > val map = Map(1 -> 2, 3 -> 4) map: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2, 3 -> 4) > map.foreach((k, v) => println(k)) error: wrong number of parameters; expected = 1 map.foreach((k, v) => println(k)) ^ > map.foreach({(k, v) => println(k)}) error: wrong number of parameters; expected = 1 map.foreach({(k, v) => println(k)}) ^ > map.foreach(case (k, v) => println(k)) error: illegal start of simple expression map.foreach(case (k, v) => println(k)) ^ I can do > map.foreach(_ match {case (k, v) => println(k)}) 1 3 Any better alternatives?

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• XSLT special characters

  - by Apurv

  In the following XSL transformation how do I output the '<' and '' symbol? Input XML: <TestResult bugnumber="3214" testname="display.methods::close->test_ManyInvoke" errortype="Failure"><ErrorMessage><![CDATA[calling close() method failed - expected:<2>]]></ErrorMessage> XSLT: <xsl:template match="TestResult"> <xsl:variable name="errorMessage"> <xsl:value-of select="ErrorMessage" disable-output-escaping="yes"/> </xsl:variable> <Test name='{@testname}'> <TestResult> <Passed>false</Passed> <State>failure</State> <Metadata> <Entry name='bugnumber' value='{@bugnumber}' /> </Metadata> <TestOutput> <Metadata> <Entry name='ErrorMessage' value='{$errorMessage}' /> </Metadata> </TestOutput> </TestResult> </Test> </xsl:template> Output XML: <Test name="display.methods::close-&gttest_ManyInvoke"> <TestResult> <Passed>false</Passed> <State>failure</State> <Metadata> <Entry name="bugnumber" value="3214"/> </Metadata> <TestOutput> <Metadata> <Entry name="ErrorMessage" value="calling close() method failed - expected:&lt;2&gt;"/> </Metadata> </TestOutput> </TestResult> </Test>

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• do the Python libraries have a natural dependence on the global namespace?

  - by msw

  I first ran into this when trying to determine the relative performance of two generators: t = timeit.repeat('g.get()', setup='g = my_generator()') So I dug into the timeit module and found that the setup and statement are evaluated with their own private, initially empty namespaces so naturally the binding of g never becomes accessible to the g.get() statement. The obvious solution is to wrap them into a class, thus adding to the global namespace. I bumped into this again when attempting, in another project, to use the multiprocessing module to divide a task among workers. I even bundled everything nicely into a class but unfortunately the call pool.apply_async(runmc, arg) fails with a PicklingError because buried inside the work object that runmc instantiates is (effectively) an assignment: self.predicate = lambda x, y: x > y so the whole object can't be (understandably) pickled and whereas: def foo(x, y): return x > y pickle.dumps(foo) is fine, the sequence bar = lambda x, y: x > y yields True from callable(bar) and from type(bar), but it Can't pickle <function <lambda> at 0xb759b764>: it's not found as __main__.<lambda>. I've given only code fragments because I can easily fix these cases by merely pulling them out into module or object level defs. The bug here appears to be in my understanding of the semantics of namespace use in general. If the nature of the language requires that I create more def statements I'll happily do so; I fear that I'm missing an essential concept though. Why is there such a strong reliance on the global namespace? Or, what am I failing to understand? Namespaces are one honking great idea -- let's do more of those!

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• Is this reference or code in mistake or bug?

  - by mikezang

  I copied some text from NSDate Reference as below, please check Return Value, it is said the format will be in YYYY-MM-DD HH:MM:SS ±HHMM, but I got as below in my app, so the reference is mistake? or code in mistake? Saturday, January 1, 2011 12:00:00 AM Japan Standard Time or 2011?1?1????0?00?00? ????? descriptionWithLocale: Returns a string representation of the receiver using the given locale. - (NSString *)descriptionWithLocale:(id)locale Parameters locale An NSLocale object. If you pass nil, NSDate formats the date in the same way as the description method. On Mac OS X v10.4 and earlier, this parameter was an NSDictionary object. If you pass in an NSDictionary object on Mac OS X v10.5, NSDate uses the default user locale—the same as if you passed in [NSLocale currentLocale]. Return Value A string representation of the receiver, using the given locale, or if the locale argument is nil, in the international format YYYY-MM-DD HH:MM:SS ±HHMM, where ±HHMM represents the time zone offset in hours and minutes from GMT (for example, “2001-03-24 10:45:32 +0600”)

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• Unexpected results when looking at ASCII codes in C++.

  - by Columbo

  Hello, The bit of code below is extracting ASCII codes from characters. When I convert characters in the normal ASCII region I get the value I expect. When I convert £ and € from the extened region I get a load of 1's padding the INT that I'm storing the character in. e.g. the output of the below is: 45 (ascii E as expected) FFFFFF80 (extended ascii € as expected but padded with ones) It's not causing me an issue but I'm just wondering why this happens. Here's the code... unsigned int asciichar[3]; string cTextToEncode = "E€"; for (unsigned int i = 0; i < cTextToEncode.length(); i++) { asciichar[i] = (unsigned int)cTextToEncode[i]; cout << hex << asciichar[i] << "\n"; } Can anyone explain why this is? Thanks

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• binding image with 2 values with convertor

  - by prince23

  hi, is it possiable to set 2 data field for an image control whiling binding **<Image Source="{Binding ItemID, Converter={StaticResource IDToImageConverter}}" Height="50" />** now here i need to add one more value Price now. need to send even price as an paramter for IDToImageConverter function how can i do it? now i need to check first price value there are 3 condition i neeed to check in my IDToImageConverter function if( price> 5o) { // then get the ItemID based on the value bind image here if(ItemID >20) { // bind image1 } if(ItemID >50) { // bind image2 } } if( price> 100) { // as above codition we do here } now how can i add these above functionality in IDToImageConverter ? any idea how i can solve it <Image Source="{Binding ItemID, Converter={StaticResource IDToImageConverter}}" Height="50" /> </DataTemplate> </data:DataGridTemplateColumn.CellTemplate> </data:DataGridTemplateColumn> </data:DataGrid.Columns> </data:DataGrid> public class IDToImageConverter : IValueConverter { public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { Uri uri = new Uri("~/Images/" + value.ToString()+ ".jpg", UriKind.Relative); return new BitmapImage(uri); } thanks in advance. for anyhelp you provide prince

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• Run code before class instanciation in ActionScript 3

  - by soow.fr

  I need to run code in a class declaration before its instanciation. This would be especially useful to automatically register classes in a factory. See: // Main.as public class Main extends Sprite { public function Main() : void { var o : Object = Factory.make(42); } } // Factory.as public class Factory { private static var _factory : Array = new Array(); public static function registerClass(id : uint, c : Class) : void { _factory[id] = function () : Object { return new c(); }; } public static function make(id : uint) : Object { return _factory[id](); } } // Foo.as public class Foo { // Run this code before instanciating Foo! Factory.registerClass(42, Foo); } AFAIK, the JIT machine for the ActionScript language won't let me do that since no reference to Foo is made in the Main method. The Foo class being generated, I can't (and don't want to) register the classes in Main: I'd like to register all the exported classes in a specific package (or library). Ideally, this would be done through package introspection, which doesn't exist in ActionScript 3. Do you know any fix (or other solution) to my design issue?

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• Use cases of [ordered], the new PowerShell 3.0 feature

  - by Roman Kuzmin

  PowerShell 3.0 CTP1 introduces a new feature [ordered] which is somewhat a shortcut for OrderedDictionary. I cannot imagine practical use cases of it. Why is this feature really useful? Can somebody provide some useful examples? Example: this is, IMHO, rather demo case than practical: $a = [ordered]@{a=1;b=2;d=3;c=4} (I do not mind if it is still useful, then I am just looking for other useful cases). I am not looking for use cases of OrderedDictionary, it is useful, indeed. But we can use it directly in v2.0 (and I do a lot). I am trying to understand why is this new feature [ordered] needed in addition. Collected use cases from answers: $hash = [ordered]@{} is shorter than $hash = New-Object System.Collections.Specialized.OrderedDictionary N.B. ordered is not a real shortcut for the type. New-Object ordered does not work. N.B. 2: But this is still a good shortcut because (I think, cannot try) it creates typical for PowerShell case insensitive dictionary. The equivalent command in v2.0 is too long, indeed: New-Object System.Collections.Specialized.OrderedDictionary]([System.StringComparer]::OrdinalIgnoreCase)

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• Capturing wildcards in java generics

  - by Rollerball

  From this orcale java tutorial: The WildcardError example produces a capture error when compiled: import java.util.List; public class WildcardError { void foo(List<?> i) { i.set(0, i.get(0)); } } After this error demonstration, they fix the problem by using a helper method: public class WildcardFixed { void foo(List<?> i) { fooHelper(i); } // Helper method created so that the wildcard can be captured // through type inference. private <T> void fooHelper(List<T> l) { l.set(0, l.get(0)); } } First, they say that the list input parameter (i) is seen as an Object: In this example, the compiler processes the i input parameter as being of type Object. Why then i.get(0) does not return an Object? if it was already passed in as such? Furthermore what is the point of using a <?> when then you have to use an helper method using <T>. Would not be better using directly which can be inferred?

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• Should a C++ constructor do real work?

  - by Wade Williams

  I'm strugging with some advice I have in the back of my mind but for which I can't remember the reasoning. I seem to remember at some point reading some advice (can't remember the source) that C++ constructors should not do real work. Rather, they should initialize variables only. The advice when on to explain that real work should be done in some sort of init() method, to be called separately after the instance was created. The situation is I have a class that represents a hardware device. It makes logical sense to me for the constructor to call the routines that query the device in order to build up the instance variables that describe the device. In other words, once new instantiates the object, the developer receives an object which is ready to be used, no separate call to object-init() required. Is there a good reason why constructors shouldn't do real work? Obviously it could slow allocation time, but that wouldn't be any different if calling a separate method immediately after allocation. Just trying to figure out what gotchas I not currently considering that might have lead to such advice.

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• Have something loaded only when JList item is visibile

  - by elvencode

  Hello, i'm implementing a Jlist populated with a lot of elements. Each element corresponds to a image so i'd like to show a resized preview of them inside each row of the list. I've implemented a custom ImageCellRenderer extending the Jlabel and on getListCellRendererComponent i create the thumbnail if there'snt any for that element. Each row corresponds to a Page class where i store the path of the image and the icon applied to the JLabel. Each Page object is put inside a DefaultListModel to populate the JList. The render code is something like this: public Component getListCellRendererComponent( JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) { Page page = (Page) value; if (page.getImgIcon() == null) { System.out.println(String.format("Creating thumbnail of %s", page.getImgFilename())); ImageIcon icon = new ImageIcon(page.getImgFilename()); int thumb_width = icon.getIconWidth() > icon.getIconHeight() ? 128 : ((icon.getIconWidth() * 128) / icon.getIconHeight()); int thumb_height = icon.getIconHeight() > icon.getIconWidth() ? 128 : ((icon.getIconHeight() * 128) / icon.getIconWidth()); icon.setImage(getScaledImage(icon.getImage(), thumb_width, thumb_height)); page.setImgIcon(icon); } setIcon(page.getImgIcon()); } I was thinking that only a certain item is visibile in the List the cell renderer is called but i'm seeing that all the thumnails are created when i add the Page object to the list model. I've tried to load the items and after set the model in the JList or set the model first and after starting appending the items but the results are the same. Is there any way to load the data only when necessary or do i need to create a custom control like a JScrollPanel with stacked items inside where i check myself the visibility of each elements? Thanks

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• Pattern for version-specific implementations of a Java class

  - by Mike Monkiewicz

  So here's my conundrum. I am programming a tool that needs to work on old versions of our application. I have the code to the application, but can not alter any of the classes. To pull information out of our database, I have a DTO of sorts that is populated by Hibernate. It consumes a data object for version 1.0 of our app, cleverly named DataObject. Below is the DTO class. public class MyDTO { private MyWrapperClass wrapper; public MyDTO(DataObject data) { wrapper = new MyWrapperClass(data); } } The DTO is instantiated through a Hibernate query as follows: select new com.foo.bar.MyDTO(t1.data) from mytable t1 Now, a little logic is needed on top of the data object, so I made a wrapper class for it. Note the DTO stores an instance of the wrapper class, not the original data object. public class MyWrapperClass { private DataObject data; public MyWrapperClass(DataObject data) { this.data = data; } public String doSomethingImportant() { ... version-specific logic ... } } This works well until I need to work on version 2.0 of our application. Now DataObject in the two versions are very similar, but not the same. This resulted in different sub classes of MyWrapperClass, which implement their own version-specific doSomethingImportant(). Still doing okay. But how does myDTO instantiate the appropriate version-specific MyWrapperClass? Hibernate is in turn instantiating MyDTO, so it's not like I can @Autowire a dependency in Spring. I would love to reuse MyDTO (and my dozens of other DTOs) for both versions of the tool, without having to duplicate the class. Don't repeat yourself, and all that. I'm sure there's a very simple pattern I'm missing that would help this. Any suggestions?

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