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• What happens when you create an instance of an object containing no state in C#?

  - by liquorice

  I am I think ok at algorithmic programming, if that is the right term? I used to play with turbo pascal and 8086 assembly language back in the 1980s as a hobby. But only very small projects and I haven't really done any programming in the 20ish years since then. So I am struggling for understanding like a drowning swimmer. So maybe this is a very niave question or I'm just making no sense at all, but say I have an object kind of like this: class Something : IDoer { void Do(ISomethingElse x) { x.DoWhatEverYouWant(42); } } And then I do var Thing1 = new Something(); var Thing2 = new Something(); Thing1.Do(blah); Thing2.Do(blah); does Thing1 = Thing2? does "new Something()" create anything? Or is it not much different different from having a static class, except I can pass it around and swap it out etc. Is the "Do" procedure in the same location in memory for both the Thing1(blah) and Thing2(blah) objects? I mean when executing it, does it mean there are two Something.Do procedures or just one?

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• Why do you program? Why do you do what you do? [closed]

  - by Pirate for Profit

  To me, writing a new program is like a puzzle. Before you write any code for a large system, you have to carefully craft each piece in your mind and imagine how all the pieces will fit together. If you don't, your solution may end up being undefined. What I mean is, I often don't know what I'm doing so I'll come to this site and beg for a code snippet, and then somehow try to hack it into my projects. I started writing GW-Basic when I was around 8 years old. Then it progressed from there, went to california university and did some Python and C++, but really didn't learn anything(college = highsk00l++). I've mostly been self-taught, took awhile to break bad habits and I'd say only in recent years would I consider myself understanding of design patterns and all that stuff (no but honestly procedural dudes, I would not want to design and maintain a large system procedurally, yous crazy). And despite my username, money has NOT been a big motivator. I've gone from job to job, I can usually get the work done perfect very quickly, any delays on my part are understandable (well about as understandable as it gets in the industry). But I ain't gonna work for peanuts because I got mouths to feed. Why do you program? Why do you do what you do?

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• PHP Multi-Domain Sessions; ini_set Not Working?

  - by SumWon

  Hello, I'm trying to set it up so if you log in to my website the session carries over to all sub-domains of my website. For example, if you go to domain.com and log in, then go to sub.domain.com, you'll already be logged in at sub.domain.com. To my understanding, you would want to use ini_set('session.cookie_domain','.domain.com') and then session_start(), then set your session variables, but this isn't working. Example of what I'm doing: Code for domain.com: <?php ini_set('session.cookie_domain','.domain.com'); session_start(); $_SESSION['variable'] = 1; ?> Code for sub.domain.com: <?php session_start(); echo $_SESSION['variable']; ?> But $_SESSION['variable'] isn't set. I've also tried using ini_set() in the sub.domain.com code, but it made no difference. I've verified that setting session.cookie_domain is working by using ini_get(). What am I doing wrong? Thanks!

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• Javascript object properties access functions in parent constructor?

  - by Bob Spryn

  So I'm using this pretty standard jquery plugin pattern whereby you can grab an api after applying the jquery function to a specific instance. This API is essentially a javascript object with a bunch of methods and data. So I wanted to essentially create some private internal methods for the object only to manipulate data etc, which just doesn't need to be available as part of the API. So I tried this: // API returned with new $.TranslationUI(options, container) $.TranslationUI = function (options, container) { // private function? function monkey(){ console.log("blah blah blah"); } // extend the default settings with the options object passed this.settings = $.extend({},$.TranslationUI.defaultSettings,options); // set a reference for the container dom element this.container = container; // call the init function this.init(); }; The problem I'm running into is that init can't call that function "monkey". I'm not understanding the explanation behind why it can't. Is it because init is a prototype method?($.TranslationUI's prototype is extended with a bunch of methods including init elsewhere in the code) $.extend($.TranslationUI, { prototype: { init : function(){ // doesn't work monkey(); // editing flag this.editing = false; // init event delegates here for // languagepicker $(this.settings.languageSelector, this.container).bind("click", {self: this}, this.selectLanguage); } } }); Any explanations would be helpful. Would love other thoughts on creating private methods with this model too. These particular functions don't HAVE to be in prototype, and I don't NEED private methods protected from being used externally, but I want to know how should I have that requirement in the future.

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• Can it be important to call remove() on an EJB 3 stateless session bean? Perhaps on weblogic?

  - by Michael Borgwardt

  I'm in the process of migrating an EJB 2 application to EJB 3 (and what a satisfying task it is to delete all those deployment descriptors!). It used to run on Weblogic and now runs on Glassfish. The task is going very smoothly, but one thing makes me wary: The current code takes great care to ensure that EJBObject.remove() is called on the bean when it's done its job, and other developers have (unfortunately very vague) memories of "bad things" happening when that was not done. However, with EJB3, the implementation class does not implement EJBObject, so there is no remove() method to be called. And my understanding is that there isn't really any point at all in calling it on stateless session beans, since they are, well, stateless. Could these "bad things" have been weblogic-specific? If not, what else? Should I avoid the full EJB3 lightweightness and keep a remote interface that extends EJBObject? Or just write it off as cargo-cult programming and delete all those try/finally clauses? I'm leaning towards the latter, but now feeling very comfortable with it.

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• What are good examples of perfectly acceptable approaches to development that are NOT test driven development (TDD)?

  - by markbruns

  The TDD cycle is test, code, refactor, (repeat) and then ship. TDD implies development that is driven by testing, specifically that means understanding requirements and then writing tests first before developing or writing code. My natural inclination is a philosophical bias in favor of TDD; I would like to be convinced that there are other approaches that now work well or even better than TDD so I have asked this question. What are examples of perfectly acceptable approaches that NOT test driven development? I can think of plenty approaches that are not TDD but could be a lot more trouble than what they are worth ... it's not moral judgement, it's just that they are cost more than they are worth ... the following are simply examples of things that might be ok as learning exercises, but approaches I'd find to be NOT acceptable in serious production and NOT TDD might include: Inspecting quality into your product -- Focusing efforts on developing a proficiency in testing/QA can be problematic, especially if you don't work on the requirements and development side first ... symptom of this include bug triaging where the developers have so many different bugs to deal with it, it is necessary to employ a form of triage -- each development cycle gets worse and worse, programmers work more and more hours, sleep less and less, struggle to keep going in death march until they are consumed. Superstition ... believing in things that you don't understand -- this would involve borrowing code that you believe has been proven or tested from somewhere, e.g. legacy code, a magic code starter wizard or an open source project, and you go forward hacking up a storm of modifications, sliding FaceBook Connect into your the user interface, inventing some new magic features on the fly (e.g. a mashup using the Twitter API, GoogleMaps API and maybe Zappos API), showing off your cool new "product" to a few people and then writing up a simple "specification" and list of "test cases" and turning that over to Mechanical Turk for testing.

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• C# language questions

  - by Water Cooler v2

  1) What is int? Is it any different from the struct System.Int32? I understand that the former is a C# alias (typedef or #define equivalant) for the CLR type System.Int32. Is this understanding correct? 2) When we say: IComparable x = 10; Is that like saying: IComparable x = new System.Int32(); But we can't new a struct, right? or in C like syntax: struct System.In32 *x; x=>someThing = 10; 3) What is String with a capitalized S? I see in Reflector that it is the sealed String class, which, of course, is a reference type, unlike the System.Int32 above, which is a value type. What is string, with an uncapitalized s, though? Is that also the C# alias for this class? Why can I not see the alias definitions in Reflector? 4) Try to follow me down this subtle train of thought, if you please. We know that a storage location of a particular type can only access properties and members on its interface. That means: Person p = new Customer(); p.Name = "Water Cooler v2"; // legal because as Name is defined on Person. but // illegal without an explicit cast even though the backing // store is a Customer, the storage location is of type // Person, which doesn't support the member/method being // accessed/called. p.GetTotalValueOfOrdersMade(); Now, with that inference, consider this scenario: int i = 10; // obvious System.object defines no member to // store an integer value or any other value in. // So, my question really is, when the integer is // boxed, what is the *type* it is actually boxed to. // In other words, what is the type that forms the // backing store on the heap, for this operation? object x = i;

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• Why is it possible to enumerate a LinqToSql query after calling Dispose() on the DataContext?

  - by DanM

  I'm using the Repository Pattern with some LinqToSql objects. My repository objects all implement IDisposable, and the Dispose() method does only thing--calls Dispose() on the DataContext. Whenever I use a repository, I wrap it in a using person, like this: public IEnumerable<Person> SelectPersons() { using (var repository = _repositorySource.GetNew<Person>(dc => dc.Person)) { return repository.GetAll(); } } This method returns an IEnumerable<Person>, so if my understanding is correct, no querying of the database actually takes place until Enumerable<Person> is traversed (e.g., by converting it to a list or array or by using it in a foreach loop), as in this example: var persons = gateway.SelectPersons(); // Dispose() is fired here var personViewModels = ( from b in persons select new PersonViewModel { Id = b.Id, Name = b.Name, Age = b.Age, OrdersCount = b.Order.Count() }).ToList(); // executes queries In this example, Dispose() gets called immediately after setting persons, which is an IEnumerable<Person>, and that's the only time it gets called. So, a couple questions: How does this work? How can a disposed DataContext still query the database for results when I walk the IEnumerable<Person>? What does Dispose() actually do? I've heard that it is not necessary (e.g., see this question) to dispose of a DataContext, but my impression was that it's not a bad idea. Is there any reason not to dispose of it?

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• What is the common way to program action listeners?

  - by Roman

  I just started to learn how to use action listeners. To my understanding it works in the following way: There are some classes which contains "addActionListener" method by default (for example classes for buttons). Using this method we add an action listener to an object. For example: listenedObject.addActionListener(listeningObject). When an action with the "listenedObject" is performed, the "actionPerformed" method of the "listeningObject" will be called. So, it means that when we program a class for the listeningObject, we need to put there "actionPerformed" method. What is not clear to me, should we create a new class for every object that we want to listen. It does not seem to me as an elegant solution. On the other hand, if we have one action listener class for all (or at least many) object, than we have a problem since a instance of this class will not know which object is calling the "actionPerformed" method (and we need to know that since actions performed by the actionPerformed differs depending on who is called for this method). In my opinion, for every listened object we need to create are "personal" action listener and we can do it by setting a specific value to the corresponding field of the action listener. But I am not sure that it is a standard way to go? How do usually people do it?

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• Difference between std::result_of and decltype

  - by Luc Touraille

  I have some trouble understanding the need for std::result_of in C++0x. If I understood correctly, result_of is used to obtain the resulting type of invoking a function object with certain types of parameters. For example: template <typename F, typename Arg> typename std::result_of<F(Arg)> invoke(F f, Arg a) { return f(a); } I don't really see the difference with the following code: template <typename F, typename Arg> auto invoke(F f, Arg a) -> decltype(f(a)) //uses the f parameter { return f(a); } or template <typename F, typename Arg> auto invoke(F f, Arg a) -> decltype(F()(a)); //"constructs" an F { return f(a); } The only problem I can see with these two solutions is that we need to either: have an instance of the functor to use it in the expression passed to decltype. know a defined constructor for the functor. Am I right in thinking that the only difference between decltype and result_of is that the first one needs an expression whereas the second does not?

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• Custom collision

  - by bali182

  I was recently assigned to create a siple game using the Corona SDK. The main pillar of the game would be a simple event: the user should put a ball in a basket, and I should be able to handle this event. Here is a picture for better understanding: I successfully managed to create the collision shape for the basket, but i have trouble with the collision of the inside of this basket. My first thought was the following: create a new shape size and position it to fit the "belly" of this basket add it to the physics-world, and listen to the collision. With hybrid drawing it looks like this: But there is a problem: if i add this shape to the physics, it wouldn't let the ball fall into the, basket, it will handle this shape as a solid object as well. So my question is: How could I get this custom object to collide, without blocking the ball to fall through it? I have read a lots of forum post with similar questions but none of them got a proper answer. There must be a way to do this in an elegant way. And one note: Please don't suggest checking the collision manually, with rectangle intersection, because in this simple case it would work, but later I may need to change the shape of the basket, and then it will be useless!

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• Adding an keyUp-event to form objects

  - by reporter

  Hello folks, I've got the issue to add a browser event to some input fields. The challenge I have to face is, that one parameter of my target function is the 'event'-variable and the second one an object. For a better understanding here some codes:The HTML object: <div id="1_dateFieldAdvanced" class="xp set"> <div id="1_dateFieldAdvanced_label" class="label">Birthday</div> <div id="1_dateFieldAdvanced_value" class="value date"> <input class="day" name="dayOfBirth" value="66" maxlength="2" type="text"> <input class="month" name="monthOfBirth" value="67" maxlength="2" type="text"> <input class="year" name="yearOfBirth" value="" maxlength="4" type="text"> </div> </div> The source code of target method is like below: function advancedDateFields(currentFieldAsObject, nextField, currentValueLength, ev){} Unfortunatly the HTML and the Javascript code is generated automatically, so I'm unable to refactore the code. My question is, how can I pass the key word 'event' and the other parameters? My tries did always fail. :-(

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• Override one css class with another?

  - by user246114

  Hi, I have a list, with an li style defined. I want to replace the style of an individual element, but it doesn't seem to have any visual effect. Example: .myList li { background-color: yellow; } .foo { background-color: green; } <ul class='myList'> <li>Hello</li> </ul> When I add an item to the list, it has the .myList li style applied properly. I try now to remove all styles and apply the foo style to a single item (using jquery): $(item).removeClass(); $(item).addClass("foo"); the item does not change color to green though, but this reports the class is set to 'foo': alert($(item).attr('class')); so I guess I'm not understanding css rules here, looks like the li class definition is just overriding whatever else I do, however I want the reverse to be true, I want to override the li style definition with foo. How do we do this? Thanks

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• Removing index.php on MAMP

  - by djeetee

  this questions was asked before and has had many responses. The problem is nothing i tried worked. Background: i use MAMP and all of my web project are located under WebProjects which I relocated out of its standard location within the MAMP folder in Applications. so my structure is something like this: Documents/WebProjects/GreatSite/Application/... What happened so far: my understanding is that removing index.php can be done either through httpd.conf or .htaccess. anytime i touched httpd.conf, Apache refuses to start. I tried various edits to .htaccess including the one in codeigniter.com/wiki/mod-rewrite and the last one from a post on SO which is this: RewriteEngine On RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule ^(.*)$ /index.php?/$1 [L] this give me the following error when i access the site: An Error Was Encountered Unable to determine what should be displayed. A default route has not been specified in the routing file. I have updated config.php to have $config['index_page'] = ''; and i have placed the .htaccess file in the GreatSite folder. One other note, my CI system folder is up a level from GreatSite. Not sure if this has any impact. also, apache has the module loaded. so, I'm hoping someone has successfully done this on MAMP and could provide direction specifically around the content of their .htaccess (or even httpd.conf), it's location and any other mods they had to make to get this going. thanks

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• Are there concurrency problems when using -performSelector:withObject:afterDelay: ?

  - by mystify

  For example, I often use this: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:someDelay]; Now, lets say I call this 10 times to perform at the exact same delay, like: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; - (void)doSomethingAfterDelay:(id)someObject { /* access an array, read stuff, write stuff, do different things that would suffer in multithreaded environments .... all operations are nonatomic! */ } I have observed pretty strange behavior when doing things like this. For my understanding, this method schedules a timer to fire on the current thread, so in this case the main thread. But since it doesn't create new threads, it actually should not be possible to run into concurrency problems, right?

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• Are there concurrency problems when using -performSelector:withObject:afterDelay: ?

  - by mystify

  For example, I often use this: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:someDelay]; Now, lets say I call this 10 times to perform at the exact same delay, like: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; - (void)doSomethingAfterDelay:(id)someObject { /* access an array, read stuff, write stuff, do different things that would suffer in multithreaded environments .... all operations are nonatomic! */ } I have observed pretty strange behavior when doing things like this. For my understanding, this method schedules a timer to fire on the current thread, so in this case the main thread. But since it doesn't create new threads, it actually should not be possible to run into concurrency problems, right?

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• why would i get a different views when called from different controller actions in asp.net-mvc

  - by ooo

  I have 2 different controller actions. As seen below, one calls the same view as the other one. The fitness version has a bunch of jquery ui tabs. public ActionResult FitnessByTab(string tab, DateTime entryDate) { return View("Fitness", GetFitnessVM(DateTime.Today.Date)); } public ActionResult Fitness() { return View(GetFitnessVM(DateTime.Today.Date)); } private FitnessVM GetFitnessVM(DateTime dt) { FitnessVM vm = new FitnessVM(); vm.Date = dt; // a bunch of other date that comes from a database return vm; } the issue is that on the action FitnessByTab() the tabs dont load correctly but on the Fitness() it loads fine. How could this be as my understanding is that they would be going through the same code path at that point. As you can see i am hard coded both to the same date to make sure its not a different date causing the issue. EDIT Issues has been solved. It was the relative referencing of all my links. I didn't get any issues until i used firebug that highlighted some missing references due to "../../" instead of Url.Content("

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• Name lookup for names not dependent on template parameter in VC++2008 Express. Is it a bug?

  - by Maciej H

  While experimenting a bit with C++ templates I managed to produce this simple code, for which the output is different, than I expected according to my understanding of C++ rules. void bar(double d) { std::cout << "bar(double) function called" << std::endl; } template <typename T> void foo(T t) { bar(3); } void bar(int i) { std::cout << "bar(int) function called" << std::endl; } int main() { foo(3); return 0; } When I compile this code is VC++2008 Express function bar(int) gets called. That would be the behaviour I would expect if bar(3);in the template body was dependent on the template parameter. But it's not. The rule I found here says "The C++ standard prescribes that all names that are not dependent on template parameters are bound to their present definitions when parsing a template function or class". Am I wrong, that "present definition" of bar when parsing the template function foo is the definition of void bar(double d);? Why it's not the case if I am wrong. There are no forward declarations of bar in this compilation unit.

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• Cookies NULL On Some ASP.NET Pages (even though it IS there!)

  - by DaveDev

  Hi folks I'm working on an ASP.NET application and I'm having difficulty in understanding why a cookie appears to be null. On one page (results.aspx) I create a cookie, adding entries every time the user clicks a checkbox. When the user clicks a button, they're taken to another page (graph.aspx) where the contents of that cookie is read. The problem is that the cookie doesn't seem to exist on graph.aspx. The following code returns null: Request.Cookies["MyCookie"]; The weird thing is this is only an issue on our staging server. This app is deployed to a production server and it's fine. It also works perfectly locally. I've put debug code on both pages: StringBuilder sb = new StringBuilder(); foreach (string cookie in Request.Cookies.AllKeys) { sb.Append(cookie.ToString() + "<br />"); } this.divDebugOutput.InnerHtml = sb.ToString(); On results.aspx (where there are no problems), I can see the cookies are: MyCookie __utma __utmb __utmz _csoot _csuid ASP.NET_SessionId __utmc On graph.aspx, you can see there is no 'MyCookie' __utma __utmb __utmz _csoot _csuid ASP.NET_SessionId __utmc With that said, if I take a look with my FireCookie, I can see that the same cookie does in fact exist on BOTH pages! WTF?!?!?!?! (ok, rant over :-) ) Has anyone seen something like this before? Why would ASP.NET claim that a cookie is null on one page, and not null on another?

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• Force calling the derived class implementation within a generic function in C#?

  - by Adam Hardy

  Ok so I'm currently working with a set of classes that I don't have control over in some pretty generic functions using these objects. Instead of writing literally tens of functions that essentially do the same thing for each class I decided to use a generic function instead. Now the classes I'm dealing with are a little weird in that the derived classes share many of the same properties but the base class that they are derived from doesn't. One such property example is .Parent which exists on a huge number of derived classes but not on the base class and it is this property that I need to use. For ease of understanding I've created a small example as follows: class StandardBaseClass {} // These are simulating the SMO objects class StandardDerivedClass : StandardBaseClass { public object Parent { get; set; } } static class Extensions { public static object GetParent(this StandardDerivedClass sdc) { return sdc.Parent; } public static object GetParent(this StandardBaseClass sbc) { throw new NotImplementedException("StandardBaseClass does not contain a property Parent"); } // This is the Generic function I'm trying to write and need the Parent property. public static void DoSomething<T>(T foo) where T : StandardBaseClass { object Parent = ((T)foo).GetParent(); } } In the above example calling DoSomething() will throw the NotImplemented Exception in the base class's implementation of GetParent(), even though I'm forcing the cast to T which is a StandardDerivedClass. This is contrary to other casting behaviour where by downcasting will force the use of the base class's implementation. I see this behaviour as a bug. Has anyone else out there encountered this?

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• GTK+ and GdkPixbuf

  - by Daniel

  Hi all, I think I've got an understanding problem of GTK. My simple application has a stream of images and I'd like to display them within my GTK Window. Up to now, it looks like this: GdkPixbuf *pb = gdk_pixbuf_new_from_data(img2, GDK_COLORSPACE_RGB, FALSE, 24/3, 320, 240, 320*3, NULL, NULL); if(pb == NULL) fprintf(stderr, "Pixbuf is null!\n"); if(image != NULL) gtk_container_remove(GTK_CONTAINER(window), image); image = gtk_image_new_from_pixbuf(pb); gtk_container_add(GTK_CONTAINER(window), image); printf("Updated!\n"); img2 is my (rgb) buffer that gets updated from a stream each time. I guess gtk_container_remove and gtk_container_add might be stupid to use for this? Here's what I've got in addition: GtkWidget *window; GtkWidget *image; gtk_init(&argc, &argv); window = gtk_window_new(GTK_WINDOW_TOPLEVEL); gtk_signal_connect(GTK_OBJECT(window), "destroy", GTK_SIGNAL_FUNC(destroy), NULL); /* ... */ start_routine_for_stream_that_calls_the_above(...) /* ... */ gtk_widget_show_all(window); gtk_main(); My problem is that it's not working this way... either I see only the last GdkPixbuf image or I see none, which is the correct behaviour ... But how do I manage it to show an (stream of) updated GdkPixbuf? Thanks for help

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• Need Explanation of couchdb reduce function

  - by Alan

  From http://wiki.apache.org/couchdb/Introduction_to_CouchDB_views The couchdb reduce function is defined as function (key, values, rereduce) { return sum(values); } key will be an array whose elements are arrays of the form [key,id] values will be an array of the values emitted for the respective elements in keys i.e. reduce([ [key1,id1], [key2,id2], [key3,id3] ], [value1,value2,value3], false) I am having trouble understanding when/why the array of keys would contain different key values. If the array of keys does contain different key values, how would I deal with it? As an example, assume that my database contains movements between accounts of the form. {"amount":100, "CreditAccount":"account_number", "DebitAccount":"account_number"} I want a view that gives the balance of an account. My map function does: emit( doc.CreditAccount, doc.amount ) emit( doc.DebitAccount, -doc.amount ) My reduce function does: return sum(values); I seem to get the expected results, however I can't reconcile this with the possibility that my reduce function gets different key values. Is my reduce function supposed to group key values first? What kind of result would I return in that case?

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• Is it possible to get a truly unique id for a particular JVM instance?

  - by Uri

  I need a way to uniquely and permanently identify an instance of the JVM from within Java code running in that JVM. That is, if I have two JVMs running at the same time on the same machine, each is distinguishable. It is also distinguishable from running JVMs on other machines and from future executions on the same machine even if the process id is reused. I figure I could implement something like this by identifying the start time, the machine MAC, and the process id, and combining them in some way. I'm wondering if there is some standard way to achieve this. Update: I see that everyone recommended a UUID for the entire session. That seems like a good idea though possibly a little too heavyweight. Here is my problem though: I want to use the JVM id to create multiple unique identifiers in each JVM execution that somehow incorporate the JVM instance. My understanding is that you shouldn't really mix other numbers into a UUID because uniqueness is no longer guaranteed. An alternative is to make the UUID into a string and chain it, but then it becomes too long. Any ideas on overcoming this?

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• How can I get 100% test coverage in a Perl module that uses DBI?

  - by BrianH

  I am a bit new to the Devel::Cover module, but have found it very useful in making sure I am not missing tests. A problem I am running into is understanding the report from Devel::Cover. I've looked at the documentation, but can't figure out what I need to test to get 100% coverage. Here is the output from the cover report: line err stmt bran cond sub pod time code ... 36 sub connect_database { 37 3 3 1 1126 my $self = shift; 38 3 100 24 if ( !$self->{dsn} ) { 39 1 7 croak 'dsn not supplied - cannot connect'; 40 } 41 *** 2 33 21 $self->{dbh} = DBI->connect( $self->{dsn}, q{}, q{} ) 42 || croak "$DBI::errstr"; 43 1 11 return $self; 44 } ... line err % l !l&&r !l&&!r expr ----- --- ------ ------ ------ ------ ---- 41 *** 33 1 0 0 'DBI'->connect($$self{'dsn'}, '', '') || croak("$DBI::errstr") And here is and example of my code that tests this specific line: my $database = MyModule::Database->new( { dsn => 'Invalid DSN' }); throws_ok( sub { $database->connect_database() }, qr/Can't connect to data source/, 'Test connection exception (invalid dsn)' ); This test passes - the connect does throw an error and fulfills my "throws_ok" test. I do have some tests that test for a successful connection, which is why I think I have 33% coverage, but if I'm reading it correctly, cover thinks I am not testing the "|| croak" part of the statement. I thought I was, with the "throws_ok" test, but obviously I am missing something. Does anyone have advice on how I can test my DBI-connect line successfully? Thanks!

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• swap! alter and alike

  - by mekka

  Hello, I am having a problem understanding how these functions update the underlying ref, atom etc. The docs say: (apply f current-value-of-identity args) (def one (atom 0)) (swap! one inc) ;; => 1 So I am wondering how it got "expanded" to the apply form. It's not mentioned what exactly 'args' in the apply form is. Is it a sequence of arguments or are these separate values? Was it "expanded" to: (apply inc 0) ; obviously this wouldnt work, so that leaves only one possibility (apply inc 0 '()) (swap! one + 1 2 3) ;; #=> 7 Was it: (apply + 1 1 2 3 '()) ;or (apply + 1 [1 2 3]) (def two (atom [])) (swap! two conj 10 20) ;; #=> [10 20] Was it: (apply conj [] [10 20]) ;or (apply conj [] 10 20 '()) If I swap with a custom function like this: (def three (atom 0)) (swap! three (fn [current elem] (println (class elem))) 10) ;;#=> java.Lang.Integer Which means that the value '10' doesnt magically get changed into a seq '(10) and leads me to the conclusion, that it gets "expanded" to: (apply f current-value-of-identity arg1 arg2 arg3... '()) Is that a correct assumption and the docs are simply lacking a better description?

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