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• java: libraries for immutable functional-style data structures

  - by Jason S

  This is very similar to another question (Functional Data Structures in Java) but the answers there are not particularly useful. I need to use immutable versions of the standard Java collections (e.g. HashMap / TreeMap / ArrayList / LinkedList / HashSet / TreeSet). By "immutable" I mean immutable in the functional sense (e.g. purely functional data structures), where updating operations on the data structure do not change the original data, but instead return a new instance of the same kind of data structure. Also typically new and old instances of the data structure will share immutable data to be efficient in time and space. From what I can tell my options include: Functional Java Scala Clojure but I'm not sure whether any of these are particularly appealing to me. I have a few requirements/desirements: the collections in question should be usable directly in Java (with the appropriate libraries in the classpath). FJ would work for me; I'm not sure if I can use Scala's or Clojure's data structures in Java w/o having to use the compilers/interpreters from those languages and w/o having to write Scala or Clojure code. Core operations on lists/maps/sets should be possible w/o having to create function objects with confusing syntaxes (FJ looks slightly iffy) They should be efficient in time and space. I'm looking for a library which ideally has done some performance testing. FJ's TreeMap is based on a red-black tree, not sure how that rates. Documentation / tutorials should be good enough so someone can get started quickly using the data structures. FJ fails on that front. Any suggestions?

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• php form submit and the resend infromation screen

  - by Para

  Hello, I want to ask a best practice question. Suppose I have a form in php with 3 fields say name, email and comment. I submit the form via POST. In PHP I try and insert the date into the database. Suppose the insertion fails. I should now show the user an error and display the form filled in with the data he previously inserted so he can correct his error. Showing the form in it's initial state won't do. So I display the form and the 3 fields are now filled in from PHP with echo or such. Now if I click refresh I get a message saying "Are you sure you want to resend information?". OK. Suppose after I insert the data I don't carry on but I redirect to the same page but with the necessary parameters in the query string. This makes the message go away but I have to carry 3 parameters in the query string. So my question is: How is it better to do this? I want to not carry around lots of parameters in the query string but also not get that error. How can this be done? Should I use cookies to store the form information.

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• Java if statement strings and more

  - by user1820578

  I have decided to try and learn a little in java tonight and i have just been trying some stuff with things i have learned. My question is in an if statement how to i make two stings to be true. Here is what i have so far. if ("male".equals(gender)) && ("brendan".equals(name)) the problem i am pretty sure is the && but i am not sure. also my other question is with gender it should either be male or female. I want to have if statement with male and another for female. For this do i just do another if. For eg if ("male".equals(gender)) && ("brendan".equals(name)) { System.out.println("blah blah"); } else { System.out.println(" wrong wrong"); } if ("female".equals(gender)) { System.out.println("blah blah2"); } else { System.out.println(" wrong wrong 2"); } hope that makes sense. Any help would be great.

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• release object of a return method object c

  - by Piero

  in run the app with the analyze build, and Xcode found me a lot of memory leak and there is one in particular that i don't know how solve here it is: - (UIView *) tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section { UIImageView *sectionImage = [[UIImageView alloc] init]; if (section == 0)sectionImage.image = [UIImage imageNamed:@"myImage.png"]; return sectionImage; } so my question is, how i can release this sectionImage? if is the return of the method? EDIT: i have another question, analyze give me another memory leak, i have this: .h @property (nonatomic, retain) NSIndexPath *directCellPath; .m @synthesize directCellPath = _directCellPath; - (id)init{ if ((self = [super initWithNibName:@"MyViewController" bundle:nil])) { self.directCellPath = [[NSIndexPath alloc] init]; } return self; } then in the code i use it and finally in the dealloc i do this: - (void)dealloc { [_directCellPath release]; [super dealloc]; } and give me a memory leak on this line: self.directCellPath = [[NSIndexPath alloc] init]; why if i have deallocated it in the dealloc?

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• Is it possible to filter data used by pivot table based on filtering the rows in a source table in Excel?

  - by Geoffrey Stoel

  I have developed a dashboard in Excel 2007 that uses one source table in a sheet (being filled with a query on our data warehouse) and multiple pivot tables making different cross sections on this data. I use the GETPIVOTDATA in almost a hundred formulas to give me the right value for a specific indicator in my dashboard. This all works fine. However I now have received the question to make the dashboard for 5 different segments. As you can imagine I don't want to create 5 different workbooks for this and need to maintain the dashboard logic on all of them. So my question is the following. Is it possible to automatically (through VBA or any other means) filter the results in my source table which is the source for my pivot tables and thus for my dashboard values. So schematically: DATABASE_VIEW -- SOURCE_TABLE -- 12 pivot tables -- 100 GETPIVOTDATA functions Preferably I would like to load all the segments in the source_table (one view on my database) and then filter the data in the source table, which results in filterd source_dat for my pivots. This way I can (without requerying the db) quickly change between segments in the dashboards (refreshing pivots only). Data in the source table has the column: CUSTOMER_SEGMENT available to filter upon. Any help is appreciated. Geoffrey

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• How to use AFIncrementalStore to binding with a NSManagedObject

  - by Matrosov Alexander

  I am searching for more information on how to use AFIncrementalStore. I need to know how to implement it step by step. Please don't down vote it, because of many resources, I really need help with this. If I understood right AFIncrementalStore it is a layer for fetching data from the server and for the mapping data model. Am I right? So I have few URL that I need to mapping into my local model. All of them use GET requests. For example base_url/api/categories I get this string in response: [{"category":{"name":"3d max","id":"1111001","users":[]}}, {"category":{"name":"photoshop","id":"1111002","users":[]}}, {"category":{"name":"auto cad","id":"1111003","users":[]}}] So I have a question how I can binding my local db with this data using AFIncrementalStore. Also if you can see there are relationships in the response string that are connected to uses. The array for users will contain id that is correspond to concert users. So I think second question is how to point that model has to have relationship.

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• Retaining Managed objects - more general retaining objects

  - by Luuk D. Jansen

  A quick question regarding Managed Objects. I created an Array with Managed Objects (in Object 1: TableViewConbtroller), and pass one of those objects to another class/object (object 2: TableCell). The original array should still be retained in the original caller class. Then Object 2 is released, does that mean that that particular item in the array is released as well, as the reference to it in Object 2 was released? I am trying to better understand how to work with ManagedObjects as I get 'Object was released' errors. [EDIT] After some experimenting I came across the following scenario: I have the main AppDelegate. In a different class I create an AppDelegate to obtain the ManagedObjectContext. appDelegate = (iDomsAppDelegate *)[[UIApplication sharedApplication] delegate]; [self setContext:[appDelegate managedObjectContext]]; When the class is finished, and I release it, the variable in the class 'appDelegate' is also released. But then the ManagedObjectContext is closed, and obvious any future attempt to use it will cause a crash. So should I leave the appDelegate unreleased? This comes to the same question as the above about when and how to release in those situations where an objects is used from another class. I think a way of putting it is, how to know when you own an object and when not.

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• Partial class or "chained inheritance"

  - by Charlie boy

  Hi From my understanding partial classes are a bit frowned upon by professional developers, but I've come over a bit of an issue; I have made an implementation of the RichTextBox control that uses user32.dll calls for faster editing of large texts. That results in quite a bit of code. Then I added spellchecking capabilities to the control, this was made in another class inheriting RichTextBox control as well. That also makes up a bit of code. These two functionalities are quite separate but I would like them to be merged so that I can drop one control on my form that has both fast editing capabilities and spellchecking built in. I feel that simply adding the code form one class to the other would result in a too large code file, especially since there are two very distinct areas of functionality, so I seem to need another approach. Now to my question; To merge these two classes should I make the spellchecking RichTextBox inherit from the fast edit one, that in turn inherits RichTextBox? Or should I make the two classes partials of a single class and thus making them more “equal” so to speak? This is more of a question of OO principles and exercise on my part than me trying to reinvent the wheel, I know there are plenty of good text editing controls out there. But this is just a hobby for me and I just want to know how this kind of solution would be managed by a professional. Thanks!

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• Why won't WPF databindings show text when ToString() has a collaborating object?

  - by Jay

  In a simple form, I bind to a number of different objects -- some go in listboxes; some in textblocks. A couple of these objects have collaborating objects upon which the ToString() method calls when doing its work -- typically a formatter of some kind. When I step through the code I see that when the databinding is being set up, ToString() is called the collaborating object is not null and returns the expected result when inspected in the debugger, the objects return the expected result from ToString() BUT the text does not show up in the form. The only common thread I see is that these use a collaborating object, whereas the other bindings that show up as expected simply work from properties and methods of the containing object. If this is confusing, here is the gist in code: public class ThisThingWorks { private SomeObject some_object; public ThisThingWorks(SomeObject s) { some_object = s; } public override string ToString() { return some_object.name; } } public class ThisDoesntWork { private Formatter formatter; private SomeObject some_object; public ThisDoesntWork(SomeObject o, Formatter f) { formatter = f; some_object = o; } public override string ToString() { return formatter.Format(some_object.name); } } Again, let me reiterate -- the ToString() method works in every other context -- but when I bind to the object in WPF and expect it to display the result of ToString(), I get nothing. Update: The issue seems to be what I see as a buggy behaviour in the TextBlock binding. If I bind the Text property to a property of the DataContext that is declared as an interface type, ToString() is never called. If I change the property declaration to an implementation of the interface, it works as expected. Other controls, like Label work fine when binding the Content property to a DataContext property declared as either the implementation or the interface. Because this is so far removed from the title and content of this question, I've created a new question here: http://stackoverflow.com/questions/2917878/why-doesnt-textblock-databinding-call-tostring-on-a-property-whose-compile-tim

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• Updating an image's ImageUrl within a Repeater

  - by Django Reinhardt

  I hope someone can help me. It's a pretty newbie question, I'm afraid. I have an image inside a repeater, and I would like to change its IMAGEURL based on parameter that's being passed to it. <asp:Repeater ID="Repeater" runat="server"> <HeaderTemplate> <asp:Image ID="imgType" runat="server" /> </HeaderTemplate> <ItemTemplate> <%# Eval("DisplayName")%> </ItemTemplate> <SeparatorTemplate> <hr /> </SeparatorTemplate> </asp:Repeater> There is a SWITCH statement in the code behind that is altering the IMAGEURL depending on what's being passed to it. Inevitably, however, the images ID ("imgType") is not visible to the SWITCH statement (presumably because it's inside a REPEATER). Any suggestions on the best way to implement this would be greatly appreciated. Sorry for such a newbie question.

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• What exactly does this PHP code do?

  - by Rob

  Alright, my friend gave me this code for requesting headers and comparing them to what the header should be. It works perfectly, but I'm not sure why. Here is the code: $headers = apache_request_headers(); $customheader = "Header: 7ddb6ffab28bb675215a7d6e31cfc759"; foreach ($headers as $header => $value) { // 1 $custom .= "$header: $value"; // 2 } $mystring = $custom; // 3 $findme = $customheader; // 4 $pos = strpos($mystring, $findme); if ($pos !== false) { // Do something } else{ exit(); } //If it doesn't match, exit. I commented with some numbers relating to the following questions: 1: What exactly is happening here? Is it setting the $headers as $header AND $value? 2: Again, don't have any idea what is going on here. 3: Why set the variable to a different variable? This is the only area where the variable is getting used, so is there a reason to set it to something else? 4: Same question as 3. I'm sorry if this is a terrible question, but its been bothering me, and I really want to know WHY it works. Well, I understand why it works, I guess I just want to know more specifically. Thanks for any insight you can provide.

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• Call .NET Webservice with Android

  - by Lasse P

  Hi, I know this question has been asked here before, but I don't think those answers were adequate for my needs. We have a SOAP webservice that is used for an iPhone application, but it is possible that we need an Android specific version or a proxy of the service, so we have the option to go with either SOAP or JSON. I have a few concerns about both methods: SOAP solution: Is it possible to generate java source code from a WSDL file, if so, will it include some kind of proxy class to invoke the webservice and will it work in the Android environment at all? Google has not provided any SOAP library in Android, so i need to use 3rd party, any suggestion? What about the performance/overhead with parsing and transmitting SOAP xml over the wire versus the JSON solution? JSON solution: There is a few classes in the Android sdk that will let me parse JSON, but does it support generic parsing, like if I want the result to be parsed as a complex type? Or would I need to implement that myself? I have read about 2 libraries before here on Stackoverflow, GSON an Jackson. What is the difference performance and usability (from a developers perspective) wise? Do you guys have any experince with either of those libraries? So i guess the big question is, what method to go with? I hope you can help me out. Thanks in advance :-)

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• I want a insert query for a temp table

  - by John Stephen

  Hi..I am using C#.Net and Sql Server ( Windows Application ). I had created a temporary table. When a button is clicked, temporary table (#tmp_emp_answer) is created. I am having another button called "insert Values" and also 5 textboxes. The values that are entered in the textbox are used and whenever com.ExecuteNonQuery(); line comes, it throws an error message Invalid object name '#tbl_emp_answer'.. Below is the set of code.. Please give me a solution. Code for insert (in insert value button): private void btninsertvalues_Click(object sender, EventArgs e) { username = txtusername.Text; examloginid = txtexamloginid.Text; question = txtquestion.Text; answer = txtanswer.Text; useranswer = txtanswer.Text; SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=tempdb;Integrated Security=True;"); SqlCommand com = new SqlCommand("Insert into #tbl_emp_answer values('"+username+"','"+examloginid+"','"+question+"','"+answer+"','"+useranswer+"')", con); con.Open(); com.ExecuteNonQuery(); con.Close(); }

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• "variable tracking" is eating my compile time!

  - by wowus

  I have an auto-generated file which looks something like this... static void do_SomeFunc1(void* parameter) { // Do stuff. } // Continues on for another 4000 functions... void dispatch(int id, void* parameter) { switch(id) { case ::SomeClass1::id: return do_SomeFunc1(parameter); case ::SomeClass2::id: return do_SomeFunc2(parameter); // This continues for the next 4000 cases... } } When I build it like this, the build time is enormous. If I inline all the functions automagically into their respective cases using my script, the build time is cut in half. GCC 4.5.0 says ~50% of the build time is being taken up by "variable tracking" when I use -ftime-report. What does this mean and how can I speed compilation while still maintaining the superior cache locality of pulling out the functions from the switch? EDIT: Interestingly enough, the build time has exploded only on debug builds, as per the following profiling information of the whole project (which isn't just the file in question, but still a good metric; the file in question takes the most time to build): Debug: 8 minutes 50 seconds Release: 4 minutes, 25 seconds

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• About Interview structure for test automation lab developers

  - by Ikaso

  Hi, I am interviewing new applicants for a team that is doing test automation on our company product(s). The team is composed of junior software developers and a team leader. The product runs on windows and has both managed and unmanaged parts. The test automation is done on both client side (user mode and kernel mode) and server side (IIS, Windows Services, backend). We are doing mainly intergration tests and black box tests. I am trying to figure out how to organize my interview. My overall idea is to ask about a project they have done, then ask some technical questions (multithreading, GC, design patterns) and one programming question. Please note that there is another interview done before me with 2 programming questions. My programming question is rather simple (for example: reversing a singly-linked linked list). My coworkers think that my questions will not find good developers since my questions are rather simple and well known, but so far most of the applicants fail those questions. My questions are: Should I change the structure of my interview for this kind of job? What questions do you ask to figure our if the applicant is test oriented? (Maybe I should provide a buggy implementation of a problem and let them find the bugs and then ask them about what tests they would have done) Regards,

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• Does .Net use Device Dependent or Device Independent Bitmaps?

  - by Brian

  When loading an image into memory, does .Net use DDB, DIB, or something else entirely? If possible, please cite your sources. I'm wondering because we currently have a classic ASP application that is using a 3rd party component to load images that is occasionally creating a “Not enough storage is available to process this command.” error. The error is very inconsistent but tends to happen on larger images (not always, but often). After resetting IIS, processing the same file again typically works just fine. After much research I have found that DDBs tend to have this problem when processing large images because they work out of video memory. Considering that we are running on a web server with an integrated video card and limited shared memory, this could certainly be our problem. We are in the early stages of converting our app to .Net and am wondering if using .Net for this might be a viable alternative to our current method which is why I am asking the question. Any advice is welcome :) but out of curiosity if nothing else, I am really hoping for an answer to the question; does .Net use DDB or DIB?

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• WCF data services (OData), query with inheritance limitation?

  - by Mathieu Hétu

  Project: WCF Data service using internally EF4 CTP5 Code-First approach. I configured entities with inheritance (TPH). See previous question on this topic: Previous question about multiple entities- same table The mapping works well, and unit test over EF4 confirms that queries runs smoothly. My entities looks like this: ContactBase (abstract) Customer (inherits from ContactBase), this entity has also several Navigation properties toward other entities Resource (inherits from ContactBase) I have configured a discriminator, so both Customer and Resource map to the same table. Again, everythings works fine on the Ef4 point of view (unit tests all greens!) However, when exposing this DBContext over WCF Data services, I get: - CustomerBases sets exposed (Customers and Resources sets seems hidden, is it by design?) - When I query over Odata on Customers, I get this error: Navigation Properties are not supported on derived entity types. Entity Set 'ContactBases' has a instance of type 'CodeFirstNamespace.Customer', which is an derived entity type and has navigation properties. Please remove all the navigation properties from type 'CodeFirstNamespace.Customer'. Stacktrace: at System.Data.Services.Serializers.SyndicationSerializer.WriteObjectProperties(IExpandedResult expanded, Object customObject, ResourceType resourceType, Uri absoluteUri, String relativeUri, SyndicationItem item, DictionaryContent content, EpmSourcePathSegment currentSourceRoot) at System.Data.Services.Serializers.SyndicationSerializer.WriteEntryElement(IExpandedResult expanded, Object element, ResourceType expectedType, Uri absoluteUri, String relativeUri, SyndicationItem target) at System.Data.Services.Serializers.SyndicationSerializer.<DeferredFeedItems>d__b.MoveNext() at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteItems(XmlWriter writer, IEnumerable`1 items, Uri feedBaseUri) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeedTo(XmlWriter writer, SyndicationFeed feed, Boolean isSourceFeed) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeed(XmlWriter writer) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteTo(XmlWriter writer) at System.Data.Services.Serializers.SyndicationSerializer.WriteTopLevelElements(IExpandedResult expanded, IEnumerator elements, Boolean hasMoved) at System.Data.Services.Serializers.Serializer.WriteRequest(IEnumerator queryResults, Boolean hasMoved) at System.Data.Services.ResponseBodyWriter.Write(Stream stream) Seems like a limitation of WCF Data services... is it? Not much documentation can be found on the web about WCF Data services (OData) and inheritance specifications. How can I overpass this exception? I need these navigation properties on derived entities, and inheritance seems the only way to provide mapping of 2 entites on the same table with Ef4 CTP5... Any thoughts?

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• DDD: Enum like entities

  - by Chris

  Hi all, I have the following DB model: **Person table** ID | Name | StateId ------------------------------ 1 Joe 1 2 Peter 1 3 John 2 **State table** ID | Desc ------------------------------ 1 Working 2 Vacation and domain model would be (simplified): public class Person { public int Id { get; } public string Name { get; set; } public State State { get; set; } } public class State { private int id; public string Name { get; set; } } The state might be used in the domain logic e.g.: if(person.State == State.Working) // some logic So from my understanding, the State acts like a value object which is used for domain logic checks. But it also needs to be present in the DB model to represent a clean ERM. So state might be extended to: public class State { private int id; public string Name { get; set; } public static State New {get {return new State([hardCodedIdHere?], [hardCodeNameHere?]);}} } But using this approach the name of the state would be hardcoded into the domain. Do you know what I mean? Is there a standard approach for such a thing? From my point of view what I am trying to do is using an object (which is persisted from the ERM design perspective) as a sort of value object within my domain. What do you think? Question update: Probably my question wasn't clear enough. What I need to know is, how I would use an entity (like the State example) that is stored in a database within my domain logic. To avoid things like: if(person.State.Id == State.Working.Id) // some logic or if(person.State.Id == WORKING_ID) // some logic

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• Request for advice about class design, inheritance/aggregation

  - by Lasse V. Karlsen

  I have started writing my own WebDAV server class in .NET, and the first class I'm starting with is a WebDAVListener class, modelled after how the HttpListener class works. Since I don't want to reimplement the core http protocol handling, I will use HttpListener for all its worth, and thus I have a question. What would the suggested way be to handle this: Implement all the methods and properties found inside HttpListener, just changing the class types where it matters (ie. the GetContext + EndGetContext methods would return a different class for WebDAV contexts), and storing and using a HttpListener object internally Construct WebDAVListener by passing it a HttpListener class to use? Create a wrapper for HttpListener with an interface, and constrct WebDAVListener by passing it an object implementing this interface? If going the route of passing a HttpListener (disguised or otherwise) to the WebDAVListener, would you expose the underlying listener object through a property, or would you expect the program that used the class to keep a reference to the underlying HttpListener? Also, in this case, would you expose some of the methods of HttpListener through the WebDAVListener, like Start and Stop, or would you again expect the program that used it to keep the HttpListener reference around for all those things? My initial reaction tells me that I want a combination. For one thing, I would like my WebDAVListener class to look like a complete implementation, hiding the fact that there is a HttpListener object beneath it. On the other hand, I would like to build unit-tests without actually spinning up a networked server, so some kind of mocking ability would be nice to have as well, which suggests I would like the interface-wrapper way. One way I could solve this would be this: public WebDAVListener() : WebDAVListener(new HttpListenerWrapper()) { } public WebDAVListener(IHttpListenerWrapper listener) { } And then I would implement all the methods of HttpListener (at least all those that makes sense) in my own class, by mostly just chaining the call to the underlying HttpListener object. What do you think? Final question: If I go the way of the interface, assuming the interface maps 1-to-1 onto the HttpListener class, and written just to add support for mocking, is such an interface called a wrapper or an adapter?

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• Some sonatype nexus questions.

  - by smallufo

  I deployed a sonatype nexus server inside my LAN , mapping some remote repositories to my public repositories : First question is , why these repositories not sync with the "real" repositories ? For example , I mapped maven central (http://repo1.maven.org/maven2) to "central" , but when I browse http://smallufo:8081/nexus/content/repositories/central/org/springframework/ , the packages are not complete , in http://repo2.maven.org/maven2/org/springframework/ , there are tons of artifacts , but I only have some of them : And versions are old ... ex : spring-core is only 2.5.6.SEC01 , but the latest version is 3.0.2.RELEASE. And my maven client seems can only find the old artifacts ... "central" is a proxy directory , it should be the same with the remote server. I tried to "Expire Cache" , "ReIndex" , "Incremental ReIndex" the whole "central" : After a long time with almost 100% java process load , the situation seems not better , just add some artifacts ... not reflecting the real "Maven Central" data... Second question , what's difference with "Expire Cache" , "ReIndex" , "Incremental ReIndex" ? Even I can "search" spring-core.3.0.2.RELEASE , my m2eclipse still cannot find it : I can also see the spring-core-3.0.2.RELEASE in the "index" , (but not available in "storage") : But why m2eclipse cannot make use of it ? it seems m2eclipse can only install artifacts in the storage , if this is how nexus works , how do I "force" download spring-core-3.0.2.RELEASE to nexus's storage ? How do I solve these strange incompatibilities ? Thanks a lot !

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• I don't like Python functions that take two or more iterables. Is it a good idea?

  - by Xavier Ho

  This question came from looking at this question on Stackoverflow. def fringe8((px, py), (x1, y1, x2, y2)): Personally, it's been one of my pet peeves to see a function that takes two arguments with fixed-number iterables (like a tuple) or two or more dictionaries (Like in the Shotgun API). It's just hard to use, because of all the verbosity and double-bracketed enclosures. Wouldn't this be better: >>> class Point(object): ... def __init__(self, x, y): ... self.x = x ... self.y = y ... >>> class Rect(object): ... def __init__(self, x1, y1, x2, y2): ... self.x1 = x1 ... self.y1 = y1 ... self.x2 = x2 ... self.y2 = y2 ... >>> def fringe8(point, rect): ... # ... ... >>> >>> point = Point(2, 2) >>> rect = Rect(1, 1, 3, 3) >>> >>> fringe8(point, rect) Is there a situation where taking two or more iterable arguments is justified? Obviously the standard itertools Python library needs that, but I can't see it being pretty in maintainable, flexible code design.

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• Inheritance and type parameters of Traversable

  - by Jesper

  I'm studying the source code of the Scala 2.8 collection classes. I have questions about the hierarchy of scala.collection.Traversable. Look at the following declarations: package scala.collection trait Traversable[+A] extends TraversableLike[A, Traversable[A]] with GenericTraversableTemplate[A, Traversable] trait TraversableLike[+A, +Repr] extends HasNewBuilder[A, Repr] with TraversableOnce[A] package scala.collection.generic trait HasNewBuilder[+A, +Repr] trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] Question: Why does Traversable extend GenericTraversableTemplate with type parameters [A, Traversable] - why not [A, Traversable[A]]? I tried some experimenting with a small program with the same structure and got a strange error message when I tried to change it to Traversable[A]: error: Traversable[A] takes no type parameters, expected: one I guess that the use of the @uncheckedVariance annotation in GenericTraversableTemplate also has to do with this? (That seems like a kind of potentially unsafe hack to force things to work...). Question: When you look at the hierarchy, you see that Traversable inherits HasNewBuilder twice (once via TraversableLike and once via GenericTraversableTemplate), but with slightly different type parameters. How does this work exactly? Why don't the different type parameters cause an error?

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• Make TBODY scrollable in Webkit browsers

  - by Andrew

  I'm aware of this question, but none of the answers work in Safari, Chrome, etc. The accepted strategy (as demonstrated here) is to set the tbody height and overflow properties like so: <table> <thead> <tr><th>This is the header and doesn't scroll</th></tr> </thead> <tbody style="height:100px; overflow:auto;"> <tr><td>content that scrolls</td></tr> <tr><td>content that scrolls</td></tr> <tr><td>content that scrolls</td></tr> <tr><td>content that scrolls</td></tr> <tr><td>content that scrolls</td></tr> <tr><td>content that scrolls</td></tr> <tr><td>content that scrolls</td></tr> </tbody> </table> Unfortunately, this does not work in any webkit browsers. There is a bug report about it that doesn't seem to be a high priority (reported June 05). So my question is: are there alternate strategies that do actually work? I've tried the two-table approach, but it's impossible to guarantee that the header will line up with the content. Do I just have to wait for Webkit to fix it?

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• How do I use an index in an array reference as a method reference in Perl?

  - by Robert P

  Similar to this question about iterating over subroutine references, and as a result of answering this question about a OO dispatch table, I was wondering how to call a method reference inside a reference, without removing it first, or if it was even possible. For example: package Class::Foo; use 5.012; #Yay autostrict! use warnings; # a basic constructor for illustration purposes.... sub new { my $class = shift; return bless {}, $class; } # some subroutines for flavor... sub sub1 { say 'in sub 1' } sub sub2 { say 'in sub 2' } sub sub3 { say 'in sub 3' } # and a way to dynamically load the tests we're running... sub sublist { my $self = shift; return [ $self->can('sub1'); $self->can('sub3'}; $self->can('sub2'); ]; } package main; my $instance = Class::Foo->new(a => 1, b => 2, c => 3); my $tests = $instance->sublist(); my $index = int(rand($#{$tests})); # <-- HERE So, at HERE, we could do: my $ref = $tests->{$index}; $instance->$ref(); but how would we do this, without removing the reference first?

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• What are major differences between C# and Java?

  - by enba

  I just want to clarify one thing. This is not a question on which one is better, that part I leave to someone else to discuss. I don't care about it. I've been asked this question on my job interview and I thought it might be useful to learn a bit more. These are the ones I could come up with: Java is "platform independent". Well nowadays you could say there is the Mono project so C# could be considered too but I believe it is a bit exaggerating. Why? Well, when a new release of Java is done it is simultaneously available on all platforms it supports, on the other hand how many features of C# 3.0 are still missing in the Mono implementation? Or is it really CLR vs. JRE that we should compare here? Java doesn't support events and delegates. As far as I know. In Java all methods are virtual Development tools: I believe there isn't such a tool yet as Visual Studio. Especially if you've worked with team editions you'll know what I mean. Please add others you think are relevant. Update: Just popped up my mind, Java doesn't have something like custom attributes on classes, methods etc. Or does it?

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