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  • Type-safe, generic, empty Collections with static generics

    - by Droo
    I return empty collections vs. null whenever possible. I switch between two methods for doing so using java.util.Collections: return Collections.EMPTY_LIST; return Collections.emptyList(); where emptyList() is supposed to be type-safe. But I recently discovered: return Collections.<ComplexObject> emptyList(); return Collections.<ComplexObject> singletonList(new ComplexObject()); etc. I see this method in Eclipse Package Explorer: <clinit> () : void but I don't see how this is done in the source code (1.5). How is this magic tomfoolerie happening!!

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  • Calling a method with an instance of derived class of derived generic type

    - by madsbirk
    Okay, so I have classes class B<T> : A<T> class L : K and a method void Method(A<K> a) {...} What I would like to do is this b = new B<L>(); Method(b); //error But it is not possible to b to the correct type. Indeed it is not possible to make this cast A<K> t = new A<L>(); //error I would really like to not have to change the internals of Method. I have no problems making changes to B and/or L. Do I have any options for making some sort of workaround? I guess it should be possible for Method to execute all of its method calls etc. on b, since B derives from A and L derives from K?

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  • Beginning Game Programming-ADVICES!

    - by udsha
    I like to continue my future career on way that I am looking to choose from few more ways I would like to do. Computer Game Programming / Networking(Security) ...etc Then It is good to know the risks having no those fields and how to begin it as a game programmer! I want those kind of advices and guidance . Can Anyone show me the path ?

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  • Cascading IEquatable(Of T)

    - by Shimmy
    Hello! I have several entities I need to make IEquatable(Of TEntity) respectively. I want them first to check equality between EntityId, then if both are zero, should check regarding to other properties, for example same contact names, same phone number etc. How is this done?

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  • Converting a list of an Structure into datatable

    - by strakastroukas
    I saw a lot of examples regarding conversion of a list to data-table. I would like to convert a list of structure into a data-table. How can i do that? My structure is like ... Structure MainStruct Dim Ans1 As String Dim Ans2 As String Dim Ans3 As String Dim Skipped As Boolean End Structure and... Dim St As New MainStruct Dim Build As New List(Of MainStruct) I would like to convert the Build to a datatable

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  • Convert a generic list to an array

    - by Freewind
    I have searched for this, but unfortunately, I don't get the correct answer. class Helper { public static <T> T[] toArray(List<T> list) { T[] array = (T[]) new Object[list.size()]; for (int i = 0; i < list.size(); i++) { array[i] = list.get(i); } return array; } } Test it: public static void main(String[] args) { List<String> list = new ArrayList<String>(); list.add("abc"); String[] array = toArray(list); System.out.println(array); } But there is an error thrown: Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String; at test.Helper.main(Helper.java:30) How to solve this?

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  • Compilers behave differently with a null parameter of a generic method

    - by Eyal Schneider
    The following code compiles perfectly with Eclipse, but fails to compile with javac: public class HowBizarre { public static <P extends Number, T extends P> void doIt(P value) { } public static void main(String[] args) { doIt(null); } } I simplified the code, so T is not used at all now. Still, I don't see a reason for the error. For some reason javac decides that T stands for Object, and then complains that Object does not conform to the bounds of T (which is true): HowBizarre.java:6: incompatible types; inferred type argument(s) java.lang.Number,java.lang.Object do not conform to bounds of type variable (s) P,T found : <P,T>void required: void doIt(null); ^ Note that if I replace the null parameter with a non-null value, it compiles fine. Which of the compilers behaves correctly and why? Is this a bug of one of them?

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  • Help Modifying Generic REST Helper PHP Example Code to Support XML DOM

    - by Jennifer Baker
    Hi! I found this example PHP source code at HTTP POST from PHP, without cURL I need some help modifying the example PHP source to support XML DOM for manipulating a REST API. I thought that if I update the CASE statement for the XML section below from $r = simplexml_load_string($res); to $r = new DOMDocument(); $r->load($res); that it would work but it doesn't. :( Any help would be appreciated. function rest_helper($url, $params = null, $verb = 'GET', $format = 'xml') { $cparams = array( 'http' => array( 'method' => $verb, 'ignore_errors' => true ) ); if ($params !== null) { $params = http_build_query($params); if ($verb == 'POST') { $cparams['http']['content'] = $params; } else { $url .= '?' . $params; } } $context = stream_context_create($cparams); $fp = fopen($url, 'rb', false, $context); if (!$fp) { $res = false; } else { // If you're trying to troubleshoot problems, try uncommenting the // next two lines; it will show you the HTTP response headers across // all the redirects: // $meta = stream_get_meta_data($fp); // var_dump($meta['wrapper_data']); $res = stream_get_contents($fp); } if ($res === false) { throw new Exception("$verb $url failed: $php_errormsg"); } switch ($format) { case 'json': $r = json_decode($res); if ($r === null) { throw new Exception("failed to decode $res as json"); } return $r; case 'xml': $r = simplexml_load_string($res); if ($r === null) { throw new Exception("failed to decode $res as xml"); } return $r; } return $res; }

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  • What is a custom collection?

    - by Win Coder
    A Group of objects. However i am having confusion in the following case. A sample class Class A { public string; } Class A_list { public A[] list; public A_list(A[] _list) { list = new A[_list.length]; for (int i = 0; i < _list.Length; i++) { list[i] = _list[i]; } } } static void Main(String[] args) { A[] names = new A[3] { new A("some"), new A("another"), new A("one"), }; A_list just_an_object = new A_list(names); } Which of the above is a custom collection the array or the object that holds array as a field or are both custom collections.

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  • How to Create a Generic Method and Create Instance of The Type

    - by DaveDev
    Hi Guys I want to create a helper method that I can imagine has a signature similar to this: public static MyHtmlTag GenerateTag<T>(this HtmlHelper htmlHelper, object obj) { // how do I create an instance of MyAnchor? // this returns MyAnchor, which has a MyHtmlTag base } When I invoke the method, I want to specify a type of MyHtmlTag, such as MyAnchor, e.g.: <%= Html.GenerateTag<MyAnchor>(obj) %> or <%= Html.GenerateTag<MySpan>(obj) %> Can someone show me how to create this method? Also, what's involved in creating an instance of the type I specified? Activator.CreateInstance()? Thanks Dave

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  • Ambiguous Generic restriction T:class vs T:struct

    - by Maslow
    This code generates a compiler error that the member is already defined with the same parameter types. private T GetProperty<T>(Func<Settings, T> GetFunc) where T:class { try { return GetFunc(Properties.Settings.Default); } catch (Exception exception) { SettingReadException(this,exception); return null; } } private TNullable? GetProperty<TNullable>(Func<Settings, TNullable> GetFunc) where TNullable : struct { try { return GetFunc(Properties.Settings.Default); } catch (Exception ex) { SettingReadException(this, ex); return new Nullable<TNullable>(); } } Is there a clean work around?

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  • Is there a way to make ToEnum generic

    - by maxfridbe
    I would like to do this but it does not work. bool TryGetEnum<TEnum, TValue>(TValue value, out TEnum myEnum) { if (Enum.IsDefined(typeof(TEnum), value)) { myEnum = (TEnum)value; return true; } return false; } Example usage: MyEnum mye; bool success = this.TryGetEnum<MyEnum,char>('c',out mye);

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  • Generic test suite for ASP.NET Membership/Role/Profile/Session Providers

    - by SztupY
    Hi! I've just created custom ASP.NET Membership, Role, Profile and Session State providers, and I was wondering whether there exists a test suite or something similar to test the implementation of the providers. I've checked some of the open source providers I could find (like the NauckIt.PostgreSQL provider), but neither of them contained unit tests, and all of the forum topics I've found mentioned only a few test cases (like checking whether creating a user works), but this is clearly not a complete test suite for a Membership provider. (And I couldn't find anything for the other three providers) Are there more or less complete test suites for the above mentioned providers, or are there custom providers out there that have at least some testing avaialable?

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  • Modeling a Generic Relationship (expressed in C#) in a Database

    - by StevenH
    This is most likely one for all you sexy DBAs out there: How would I effieciently model a relational database whereby I have a field in an "Event" table which defines a "SportType"? This "SportsType" field can hold a link to different sports tables E.g. "FootballEvent", "RubgyEvent", "CricketEvent" and "F1 Event". Each of these Sports tables have different fields specific to that sport. My goal is to be able to genericly add sports types in the future as required, yet hold sport specific event data (fields) as part of my Event Entity. Is it possible to use an ORM such as NHibernate / Entity framework / DataObjects.NET which would reflect such a relationship? I have thrown together a quick C# example to express my intent at a higher level: public class Event<T> where T : new() { public T Fields { get; set; } public Event() { EventType = new T(); } } public class FootballEvent { public Team CompetitorA { get; set; } public Team CompetitorB { get; set; } } public class TennisEvent { public Player CompetitorA { get; set; } public Player CompetitorB { get; set; } } public class F1RacingEvent { public List<Player> Drivers { get; set; } public List<Team> Teams { get; set; } } public class Team { public IEnumerable<Player> Squad { get; set; } } public class Player { public string Name { get; set; } public DateTime DOB { get; set;} }

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  • C programming getting back into it - the red pill

    - by JavaRocky
    Can someone provide recommended reading, website resources or best practices to follow when programming with C. I am a proficient software developer with strong skills in Java and PHP. Is there standard libraries these days which people use? Like what spring is to java? And standard design patterns for managing memory or even standard libraries for that fact? I want to write solid, maintainable C programs. GO THE RED PILL! :P

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  • How to call notifyDataSetChanged() from a generic Adapter

    - by Matty F
    An OnItemClickListener for a ListView has the following method: @Override public void onItemClick(AdapterView<?> parent, View v, int position, long id) I'd like to have the adapter behind the ListView refresh, and I believe this is done through the use of: BaseAdapter.notifyDataSetChanged() How do I use the parent parameter in the onItemClick method to do this? So far I've tried: parent.getAdapter().notifyDataSetChanged(); This throws an error because the object returned is of class HeaderViewListAdapter, which for reasons unknown isn't a subclass of BaseAdapter.

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  • Common programming mistakes in .Net when handling exceptions?

    - by Jared Coleson
    What are some of the most common mistakes you've seen made when handling exceptions? It seems like exception handling can be one of the hardest things to learn how to do "right" in .Net. Especially considering the currently #1 ranked answer to Common programming mistakes for .NET developers to avoid? is related to exception handling. Hopefully by listing some of the most common mistakes we can all learn to handle exceptions better.

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  • distributed system programming with php

    - by ranganaMIT
    Hi guys, I'm doing a system for a hospital in my country as the final year project of my degree, my supervisor specially asked me to use php and mysql for this. i don't have any experience with distributed systems and php programming, can any one help me out to build my base and improove my knowledge stating some sites, books to refer to overcome this matter. regards, rangana.

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  • Great programming quotes

    - by epatel
    There are a lot of great programming quotes out there. Which do you like? Today (Sept 12, 2008) I heard a new one from a friend, Lars-Gunnar, he said "Gud finns i Emacs" (in Swedish). This basically means "God is in Emacs". Still laughing about it here :) What he meant was that a function "gud is grand-unified-debugger" is in Emacs. A great one I think all programmers should know is The Three Great Virtues of a Programmer.

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  • Have you ever tried programming in Malbolge?

    - by eleven81
    Have you ever tried programming in Malbolge? I have read some of the top links returned by google, here, here, here, and here. I am very intrigued by this prospect, and would like to start playing around. For those of you who have dabbled in Malbolge before, what experiences did you have? Did you have any success? How did you get started, and where did you end up? Thanks!

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