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• Scala method where type of second parameter equals part of generic type from first parameter

  - by ifischer

  I want to create a specific generic method in Scala. It takes two parameters. The first is of the type of a generic Java Interface (it's from the JPA criteria query). It currently looks like this: def genericFind(attribute:SingularAttribute[Person, _], value:Object) { ... } // The Java Interface which is the type of the first parameter in my find-method: public interface SingularAttribute<X, T> extends Attribute<X, T>, Bindable<T> Now i want to achieve the following: value is currently of type java.lang.Object. But I want to make it more specific. Value has to be the of the same type as the placeholder "_" from the first parameter (and so represents the "T" in the Java interface). Is that somehow possible, and how? BTW Sorry for the stupid question title (any suggestions?)

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• C# vs Java - Generic Lists

  - by Kevin

  What are the differences of the C# and Java implementations of the generic List class?

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• c# Generic List

  - by user177883

  I m populating data for different entities into set of lists using generic lists as follows : List<Foo> foos .. List<Bar> bars .. I need to write these lists to a file, i do have a util method to get the values of properties etc. using reflection. What i want to do is: using a single method to write these into files such as: void writeToFile(a generic list) { //Which i will write to file here. } How can i do this? I want to be able to call : writeToFile(bars); writeToFile(foos);

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• REG GENERIC METHOD

  - by googler1

  Hi buddies, I had a thought on using the generic method in c# as like we do in c++. Normally a method looks like this: public static (void/int/string) methodname((datatype) partameter) { return ...; } I had a thought whether can we implement the generics to this method like this: public static <T> methodname(<T> partameter) { return ...; } Using as a generic to define the datatype. Can anyone pls suggest whether the above declaration is correct and can be used in c#? Thanks in advance.

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• Middleware with generic communication media layer

  - by Tom

  Greetings all, I'm trying to implement middleware (driver) for an embedded device with generic communication media layer. Not sure what is the best way to do it so I'm seeking an advice from more experienced stackoverflow users:). Basically we've got devices around the country communicating with our servers (or a pda/laptop in used in field). Usual form of communication is over TCP/IP, but could be also using usb, RF dongle, IR, etc. The plan is to have object corresponding with each of these devices, handling the proprietary protocol on one side and requests/responses from other internal systems on the other. The thing is how create something generic in between the media and the handling objects. I had a play around with the TCP dispatcher using boost.asio but trying to create something generic seems like a nightmare :). Anybody tried to do something like that? What is the best way how to do it? Example: Device connects to our Linux server. New middleware instance is created (on the server) which announces itself to one of the running services (details are not important). The service is responsible for making sure that device's time is synchronized. So it asks the middleware what is the device's time, driver translates it to device language (protocol) and sends the message, device responses and driver again translates it for the service. This might seem as a bit overkill for such a simple request but imagine there are more complex requests which the driver must translate, also there are several versions of the device which use different protocol, etc. but would use the same time sync service. The goal is to abstract the devices through the drivers to be able to use the same service to communicate with them. Another example: we find out that the remote communications with the device are down. So we send somebody out with PDA, he connects to the device using USB cable. Starts up the application which has the same functionality as the timesync service. Again middleware instance is created (on the PDA) to translate communication between application and the device this time only using USB/serial media not TCP/IP as in previous example. I hope it makes more sense now :) Cheers, Tom

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• A generic error occurred in GDI+.

  - by Pinu

  A generic error occurred in GDI+ [ExternalException (0x80004005): A generic error occurred in GDI+.] System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderParameters encoderParams) +615257 I have a webpage in which a pdf is converted to png, and using the response.outputstream it is displayed. when i run this on my local machine is works fine. but when i run the same code on server is throws this exception. my question is , where i could look in for error. as there is no inner exception or any other information provided. only clue is that it's happening on Image.Save , but the same code works perfectly fine on my local machine , then y is it not working on production???

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• Edit the opposite side of a many to many relationship with django generic form

  - by Ed

  I have two models: class Actor(models.Model): name = models.CharField(max_length=30, unique = True) event = models.ManyToManyField(Event, blank=True, null=True) class Event(models.Model): name = models.CharField(max_length=30, unique = True) long_description = models.TextField(blank=True, null=True) In a previous question: http://stackoverflow.com/questions/2503243/django-form-linking-2-models-by-many-to-many-field, I created an EventForm with a save function: class EventForm(forms.ModelForm): class Meta: model = Event def save(self, commit=True): instance = forms.ModelForm.save(self) instance.actors_set.clear() for actor in self.cleaned_data['actors']: instance.actors_set.add(actors) return instance This allowed me to add m2m links from the other side of the defined m2m connection. Now I want to edit the entry. I've been using a generic function: def generic_edit(request, modelname, object_id): modelname = modelname.lower() form_class = form_dict[modelname] return update_object(request, form_class = form_class, object_id = object_id, template_name = 'createdit.html' ) but this pulls in all the info except the many-to-many selections saved to this object. I think I need to do something similar to this: http://stackoverflow.com/questions/1700202/editing-both-sides-of-m2m-in-admin-page, but I haven't figured it out. How do I use the generic update_object to edit the other side of many-to-many link?

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• Can't Use Generic C# Class in Using Statement

  - by Eric J.

  I'm trying to use a generic class in a using statement but the compiler can't seem to treat it as implementing IDisposable. using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Data.Objects; namespace Sandbox { public sealed class UnitOfWorkScope<T> where T : ObjectContext, IDisposable, new() { public void Dispose() { } } public class MyObjectContext : ObjectContext, IDisposable { public MyObjectContext() : base("DummyConnectionString") { } #region IDisposable Members void IDisposable.Dispose() { throw new NotImplementedException(); } #endregion } public class Consumer { public void DoSomething() { using (new UnitOfWorkScope<MyObjectContext>()) { } } } } Compiler error is: Error 1 'Sandbox.UnitOfWorkScope<Sandbox.MyObjectContext>': type used in a using statement must be implicitly convertible to 'System.IDisposable' I implemented IDisposable on UnitOfWorkScope (and to see if that was the problem, also on MyObjectContext). What am I missing?

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• Uses for static generic classes?

  - by Hightechrider

  What are the key uses of a Static Generic Class in C#? When should they be used? What examples best illustrate their usage? e.g. public static class Example<T> { public static ... } Since you can't define extension methods in them they appear to be somewhat limited in their utility. Web references on the topic are scarce so clearly there aren't a lot of people using them. Here's a couple:- http://ayende.com/Blog/archive/2005/10/05/StaticGenericClass.aspx http://stackoverflow.com/questions/686630/static-generic-class-as-dictionary

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• ASP.NET MVC Generic Controllers and Spring.NET

  - by Jason

  Hello, I am creating an application using ASP.NET MVC (2) and Spring.NET. Since most of my Controller implementations just implement the similar CRUD operations, I would like to just create a single Generic controller, as explained here: http://stackoverflow.com/questions/848904/in-asp-net-mvc-is-it-possible-to-make-a-generic-controller However, the above example doesn't take DI frameworks into consideration. What I'm thinking is to create this (warning: this is an ugly mass of code I need help with): public SpringGenericControllerFactory : DefaultControllerFactory { public IController CreateController(RequestContext requestContext, string controllerName) { // Determine the controller type to return Type controllerType = Type.GetType("MyController").MakeGenericType(Type.GetType(controllerName)); // Return the controller return Activator.CreateInstance(controllerType) as IController; } } The entries in objects.xml would look something like this: <object id="controllerFactory" type="Application.Controllers.SpringGenericControllerFactory" /> <object id="DepartmentController" factory-method="CreateController" factory-object="controllerFactory" /> Can anyone pick through this and offer advice?

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• How to create a complete generic TreeView like data structure

  - by Nima Rikhtegar

  I want to create a completely generic treeview like structure. some thing like this: public class TreeView<T, K, L> { public T source; public K parent; public List<L> children; } as you can see in this class source, parent and also the children, all have a different generic data type. also i want my tree view to have unlimited number of levels (not just 3). this way when i want to work with my nodes in the code, all of them are going to be strongly typed. not just objects that i need to convert them to their original type. is it possible to create this kind of structure in c#, a treeview which all of its nodes are strongly typed? thanks

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• Doing a generic <sql:query> in Grails

  - by melling

  This is a generic way to select data from a table and show the results in an HTML table using JSP taglibs. What is the generic way to do this in Grails? That is, take a few lines of SQL and generate an HTML table from scratch in Grails, including the column names as headers. <sql:query var="results" dataSource="${dsource}" select * from foo </sql:query (# of rows: ${results.rowCount}) <table border="1" <!-- column headers -- <tr bgcolor=cyan <c:forEach var="columnName" items="${results.columnNames}" <th<c:out value="${columnName}"/</th </c:forEach </tr <!-- column data -- <c:forEach var="row" items="${results.rowsByIndex}" <tr <c:forEach var="column" items="${row}" <td<c:out value="${column}"/</td </c:forEach </tr </c:forEach </table The solution to this was answered in another StackOverFlow question. http://stackoverflow.com/questions/425294/sql-database-views-in-grails IF SOMEONE WRITES A GOOD ANSWER, I'LL ACCEPT IT. I would like a 100% acceptance on all of my questions.

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• Generic List .First not working LINQ

  - by Hurricanepkt

  var stuff = ctx.spReport(); var StuffAssembled = new List<ReportCLS>(); var val = new List<ReportCLS>(); foreach (var item in stuff) { StuffAssembled.Add(new ReportCLS(item)); } val.Add(StuffAssembled.First()); Keeps throwing System.Collections.Generic.List' does not contain a definition for 'First' and no extension method 'First' accepting a first argument of type 'System.Collections.Generic.List' could be found (are you missing a using directive or an assembly reference?) what is going wrong ? moreover how do i fix it? Thanks

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• Initialize generic object from a System.Type

  - by CaptnCraig

  I need to create a generic type, but I do not know the type at compile time. I would like to do this: Type t = typeof(whatever); var list = new List<t> this won't compile, because t is not a valid type. But it does know all about a valid type. Is there a way to dynamically create the generic list from a System.Type like this? I may need reflection, and that's ok, I am just a bit lost here.

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• Accessing properties through Generic type parameter

  - by Veer

  I'm trying to create a generic repository for my models. Currently i've 3 different models which have no relationship between them. (Contacts, Notes, Reminders). class Repository<T> where T:class { public IQueryable<T> SearchExact(string keyword) { //Is there a way i can make the below line generic //return db.ContactModels.Where(i => i.Name == keyword) //I also tried db.GetTable<T>().Where(i => i.Name == keyword) //But the variable i doesn't have the Name property since it would know it only in the runtime //db also has a method ITable GetTable(Type modelType) but don't think if that would help me } } In MainViewModel, I call the Search method like this: Repository<ContactModel> _contactRepository = new Repository<ContactModel>(); public void Search(string keyword) { var filteredList = _contactRepository.SearchExact(keyword).ToList(); } I use Linq-To-Sql.

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• Retrieving the MethodInfo of of the correct overload of a generic method

  - by Anne

  I have this type that contains two overloads of a generic method. I like to retrieve one of the overloads (with the Func<T> parameter) using reflection. The problem however is that I can't find the correct parameter type to supply the Type.GetMethod(string, Type[]) method with. Here is my class definition: public class Foo { public void Bar<T>(Func<T> f) { } public void Bar<T>(Action<T> a) { } } And this is what I've come up with, unfortunately without succes: [TestMethod] public void Test1() { Type parameterType = typeof(Func<>); var method = typeof(Foo).GetMethod("Bar", new Type[] { parameterType }); Assert.IsNotNull(method); // Fails } How can I get the MethodInfo of a generic method of which I know the parameters?

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• Interface with generic parameters- can't get it to compile

  - by user997112

  I have an interface like so: public interface MyInterface<E extends Something1> { public void meth1(MyClass1<E> x); } and I have a subclass whose superclass implements the above interface: public class MyClass2<E extends Something1> extends Superclass{ public MyClass2(){ } public void meth1(MyClass1 x) { // TODO Auto-generated method stub } } superclass: public abstract class Superclass<E extends Something1> implements MyInterface{ MyClass1<E> x; protected E y; public Superclass(){ } } the problem is that the parameter for meth1() is supposed to be generic. If I do MyClass1 it doesn't like it and the only way I can get it to compile is by leaving out generic parameters- which feels wrong. What's going wrong?

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• using AutoCompleteTextField in wicket without String as the generic type

  - by Manuel

  Hi! This question follows this: handling to onchange event of AutoCompleteTextField in wicket I'm trying to use the AutoCompleteTextField with a custom class as the generic type, and to add an AjaxFormComponentUpdatingBehavior. What I mean is I want to have a AutoCompleteTextField<SomeClass> myAutoComplete = ...; and after that add a AjaxFormComponentUpdatingBehavior: myAutoComplete.add(new AjaxFormComponentUpdatingBehavior("onchange") { @Override protected void onUpdate(AjaxRequestTarget target) { System.out.println( "Value: "+getValue() ); } }); The problem is that for some reason, adding that behavior makes the form try to set the model object with a String (even though the AutoCompleteTextField has a generic type of SomeClass), causing a ClassCastException when the onchange event fires. Is there a way to use AutoCompleteTextField without it being AutoCompleteTextField<String>? I couldn't find any example. Thanks for your time! and thanks to the user biziclop for his help in this matter.

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• Java-syntax for explicitly specifiying generic arguments in method calls

  - by hstoerr

  What is the syntax for explicitly giving the type parameters for a generic Java method?

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• Generic Dictionary - Getting Convertion Error

  - by pm_2

  The following code is giving me an error: // GetDirectoryList() returns Dictionary<string, DirectoryInfo> Dictionary<string, DirectoryInfo> myDirectoryList = GetDirectoryList(); // The following line gives a compile error foreach (Dictionary<string, DirectoryInfo> eachItem in myDirectoryList) The error it gives is as follows: Cannot convert type 'System.Collections.Generic.KeyValuePair<string,System.IO.DirectoryInfo>' to 'System.Collections.Generic.Dictionary<string,System.IO.DirectoryInfo>’ My question is: why is it trying to perform this conversion? Can I not use a foreach loop on this type of object?

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• MVC Display Template for Generic Type

  - by Kyle

  I am trying to use the model ListModel as a generic list model. I would like to enter on the page @Html.DisplayForModel() However the MVC is not correctly finding the templated file "ListModel.cshtml". It must work differently for generic models. What should I name the templated file in order for it to correctly be located? public class ListModel<T> { public IEnumerable<T> Models {get;set;} public string NextPage {get;set;} } I would expect it to look for "Shared/DisplayTemplates/ListModel.ascx" but it doesn't. Does anyone know?

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• A generic list of generics

  - by SnOrfus

  I'm trying to store a list of generic objects in a generic list, but I'm having difficulty declaring it. My object looks like: public class Field<T> { public string Name { get; set; } public string Description { get; set; } public T Value { get; set; } /* ... */ } I'd like to create a list of these. My problem is that each object in the list can have a separate type, so that the populated list could contain something like this: { Field<DateTime>, Field<int>, Field<double>, Field<DateTime> } So how do I declare that? List<Field<?>> (I'd like to stay as typesafe as possible, so I don't want to use an ArrayList).

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• Java generic Interface performance

  - by halfwarp

  Simple question, but tricky answer I guess. Does using Generic Interfaces hurts performance? Example: public interface Stuff<T> { void hello(T var); } vs public interface Stuff { void hello(Integer var); <---- Integer used just as an example } My first thought is that it doesn't. Generics are just part of the language and the compiler will optimize it as though there were no generics (at least in this particular case of generic interfaces). Is this correct?

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• Generic Dictionary - Getting Conversion Error

  - by pm_2

  The following code is giving me an error: // GetDirectoryList() returns Dictionary<string, DirectoryInfo> Dictionary<string, DirectoryInfo> myDirectoryList = GetDirectoryList(); // The following line gives a compile error foreach (Dictionary<string, DirectoryInfo> eachItem in myDirectoryList) The error it gives is as follows: Cannot convert type 'System.Collections.Generic.KeyValuePair<string,System.IO.DirectoryInfo>' to 'System.Collections.Generic.Dictionary<string,System.IO.DirectoryInfo>’ My question is: why is it trying to perform this conversion? Can I not use a foreach loop on this type of object?

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• Using Include() with inherited entities problem

  - by Peter Stegnar

  In EF eager loading related entities is easy. But I'm having difficulties including inherited entities when loading data using table-per-type model. This is my model: Entities: ArticleBase (base article entity) ArticleSpecial (inherited from ArticleBase) UserBase (base user entity) UserSpecial (inherited from UserBase) Image Relations are as shown on the image (omitting many columns): In reality my users are always of type UserSpecial, since UserBase is used in another application, thus we can share credentials. That's the only reason I have two separate tables. UserBase table can't be changed in any way shape or form, because the other app would break. Question How am I suppose to load ArticleSpecial with both CreatedBy and EditedBy set, so that both are of type UserSpecial (that defines Image relation)? I've tried (unsuccessfully though) these options: 1. Using lambda expressions: context.ArticleBases .OfType<ArticleSpecial>() .Include("UserCreated.Image") .Include("UserEdited.Image"); In this case the problem is that both CreatedBy and EditedBy are related to UserBase, that doesn't define Image navigation. So I should somehow cast these two to UserSpecial type like: context.ArticleBases .OfType<ArticleSpecial>() .Include("UserCreated<UserSpecial>.Image") .Include("UserEdited<UserSpecial>.Image"); But of course using generics in Include("UserCreated<UserSpecial>.Image") don't work. 2. I have tried using LINQ query var results = from articleSpecial in ctx.ArticleBase.OfType<ArticleSpecial>() join created in ctx.UserBase.OfType<UserSpecial>().Include("Image") on articleSpecial.UserCreated.Id equals created.Id join edited in ctx.UserBase.OfType<UserSpecial>().Include("Image") on articleSpecial.UserEdited.Id equals edited.Id select articleSpecial; In this case I'm only getting ArticleSpecial object instances without related properties being set. I know I should select those somehow, but I don't know how? Select part in my LINQ could be changed to something like select new { articleSpecial, articleSpecial.UserCreated, articleSpecial.UserEdited }; but images are still not loaded into my context. My joins in this case are barely used to filter out articleSpecial results, but they don't load entities into context (I suppose). Can anybody provide any help regarding this problem? I think it's not so uncommon.

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