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  • Generic Factorial function in C#

    - by mqpasta
    I want to write a generic function to calculate factorial in C# ... like: static T Factorial<T>(T n) { if (n <= 1) return 1; return Factorial<T>(n - 1); } but obviously having restriction that we can't perform operations on type 'T'. any alternative?

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  • how to implement class with collection of string/object pairs so that an object can be returned with

    - by matti
    The values in a file are read as string and can be double, string or int or maybe even lists. An example file: DatabaseName=SomeBase Classes=11;12;13 IntValue=3 //this is required! DoubleValue=4.0 I was thinking something like this: public static T GetConfigValue(string cfgName) { // here we just return for example the value which could // be List[int] if parameter cfgName='Classes' // and LoadConfig was called with Dictionary containing // keyvaluepair 'Classes' / typeof(List[int]) } public static bool LoadConfig(Dictionary reqSettings, Dictionary optSettings) { foreach (KeyValuePair kvPair in reqSettings) { if (ReadCheckAndStore(kVPair, true)) return false; } foreach (KeyValuePair kvPair in reqSettings) { if (ReadCheckAndStore(kVPair, false)) return false; } return true; } private static bool ReadCheckAndStore(KeyValuePair kVPair, bool isRequired) { if (!ReadValue(kVPair.Key, out confValue) && isRequired) //req. IntValue !found return false; //here also have to test if read value is wanted type. //and if yes store to collection. } Thanks a lot & BR! -Matti PS. Additional issue is default values for optional settings. It's not elegant to pass them to LoadConfig in separate Dictionary, but that is an other issue...

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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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  • How to Pass Parameters to Activator.CreateInstance<T>()

    - by DaveDev
    Hi guys I want to create an instance of a type that I specify in a generic method that I have. This type has a number of overloaded constructors. I'd like to be able to pass arguments to the constructors, but Activator.CreateInstance<T>() doesn't see to have this as an option. Is there another way to do it? 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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  • .NET template class instance - passing a variable data type

    - by FerretallicA
    As the title suggests, I'm tyring to pass a variable data type to a template class. Something like this: frmExample = New LookupForm(Of Models.MyClass) 'Works fine Dim SelectedType As Type = InstanceOfMyClass.GetType() 'Works fine frmExample = New LookupForm(Of SelectedType) 'Ba-bow! frmExample = New LookupForm(Of InstanceOfMyClass.GetType()) 'Ba-bow! LookupForm<Models.MyClass> frmExample; Type SelectedType = InstanceOfMyClass.GetType(); frmExample = new LookupForm<SelectedType.GetType()>(); //Ba-bow frmExample = new LookupForm<(Type)SelectedType>(); //Ba-bow I'm assuming it's something to do with the template being processed at compile time but even if I'm off the mark there, it wouldn't solve my problem anyway. I can't find any relevant information on using Reflection to instance template classes either. (How) can I create an instance of a dynamically typed repository at runtime?

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  • Generic type in generic collection

    - by Brian Triplett
    I have generic type that looks like: public class GenericClass<T, U> where T : IComparable<T> { // Class definition here } I then have a collection of these instances. What is the cleanest way to pass through the type constraints? public class GenericCollection<V> where V : GenericClass<T, U> // This won't compile { private GenericClass<T, U>[] entries; public V this[index] { get{ return this.entries[index]; } } } Is there perhaps a better way to design this? I think that specifying GenericCollection<T, U, V> where V : GenericClass<T, U> seems awkward. Might be my only option though....

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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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  • adhoc struct/class in C#?

    - by acidzombie24
    Currently i am using reflection with sql. I find if i want to make a specialize query it is easiest to get the results by creating a new class inheriting from another and adding the 2 members/columns for my specialized query. Then due to reflections in the lib in my c# code i can write foreach(var v in list) { v.AnyMember and v.MyExtraMember) Now instead of having the class scattered around or modifying my main DB.cs file can i define a class inside a function? I know i can create an anonymous object by writing new {name=val, name2=...}; but i need a to pass this class in a generic function func(query, args);

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  • What would be the best .NET 2.0 type to represent .NET 3.5 HashSet<T>?

    - by Will Marcouiller
    I'm writing myself a class library to manage Active Directory. I have an interface: Public Interface ISourceAnnuaire(Of T as {IGroupe, ITop, IUniteOrganisation, IUtilisateur}) Readonly Property Changements As Dictionary(Of T, HashSet(Of String)) End Interface This Changements property is used to save in memory the changes that occur on a particular element that is part of the source. However, I am stuck with .NET Framework 2.0. What would be the closest .NET 2.0 for HashSet(Of String)?

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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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  • How to pass an IronPython instance method to a (C#) function parameter of type `Func<Foo>`

    - by Daren Thomas
    I am trying to assign an IronPython instance method to a C# Func<Foo> parameter. In C# I would have a method like: public class CSharpClass { public void DoSomething(Func<Foo> something) { var foo = something() } } And call it from IronPython like this: class IronPythonClass: def foobar(): return Foo() CSharpClass().DoSomething(foobar) But I'm getting the following error: TypeError: expected Func[Foo], got instancemethod

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  • Define Default constructor Structuremap in a Generic Repository

    - by Ricky
    Hello guys, I have a generic IRepository that has 2 constructors, one have none parameters, other has the datacontext as parameter. I want to define to structuremap to aways in this case use the parameterless constructor. I want a way to create a parameterless contructor, other solutions that I have seen, they create a new Datacontext and pass it to the constructor that has parameters.

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  • eclipse helios tomcat error

    - by itsraja
    Hi, I just created a struts application in eclipse Helios. when I run as server I get an alert like this. My browser is online only. This document cannot be displayed while offline. To go online, uncheck Work Offline from the File menu. and this is error displayed. Dec 23, 2010 7:20:37 PM org.apache.catalina.core.AprLifecycleListener init SEVERE: An incompatible version 1.1.15 of the APR based Apache Tomcat Native library is installed, while Tomcat requires version 1.1.17 Dec 23, 2010 7:20:37 PM org.apache.tomcat.util.digester.SetPropertiesRule begin WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:StrutsHelloWorld' did not find a matching property. Dec 23, 2010 7:20:37 PM org.apache.coyote.http11.Http11Protocol init INFO: Initializing Coyote HTTP/1.1 on http-8080 Dec 23, 2010 7:20:37 PM org.apache.catalina.startup.Catalina load INFO: Initialization processed in 1081 ms Dec 23, 2010 7:20:37 PM org.apache.catalina.core.StandardService start INFO: Starting service Catalina Dec 23, 2010 7:20:37 PM org.apache.catalina.core.StandardEngine start INFO: Starting Servlet Engine: Apache Tomcat/6.0.29 Dec 23, 2010 7:20:38 PM org.apache.catalina.core.StandardContext filterStart SEVERE: Exception starting filter struts2 java.lang.ClassNotFoundException: org.apache.struts2.dispatcher.FileDispatcher at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1645) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1491) at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:269) at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:422) at org.apache.catalina.core.ApplicationFilterConfig.(ApplicationFilterConfig.java:115) at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4001) at org.apache.catalina.core.StandardContext.start(StandardContext.java:4651) at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045) at org.apache.catalina.core.StandardHost.start(StandardHost.java:785) at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045) at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:445) at org.apache.catalina.core.StandardService.start(StandardService.java:519) at org.apache.catalina.core.StandardServer.start(StandardServer.java:710) at org.apache.catalina.startup.Catalina.start(Catalina.java:581) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289) at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414) Dec 23, 2010 7:20:38 PM org.apache.catalina.core.StandardContext start SEVERE: Error filterStart Dec 23, 2010 7:20:38 PM org.apache.catalina.core.StandardContext start SEVERE: Context [/StrutsHelloWorld] startup failed due to previous errors Thanks.

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  • Casting Between Data Types in C#

    - by Jimbo
    I have (for example) an object of type A that I want to be able to cast to type B (similar to how you can cast an int to a float) Data types A and B are my own. Is it possible to define the rules by which this casting occurs? Example int a = 1; float b = (float)a; int c = (int)b;

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  • To Reference A Generic Method With A Lambda Expression

    - by SDReyes
    It is possible to reference a generic method using a Lambda Expression Object? For example, having: TheObject: public abstract class LambdaExpression : Expression TheMethod (an extension method of LINQ): public static TSource Last<TSource>( this IEnumerable<TSource> source ) I'm trying to create an instance of TheObject, that references to TheMethod. How do you do such thing?

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  • Class hierarchy problem (with generic's variance!)

    - by devoured elysium
    The problem: class StatesChain : IState, IHasStateList { private TasksChain tasks = new TasksChain(); ... public IList<IState> States { get { return _taskChain.Tasks; } } IList<ITask> IHasTasksCollection.Tasks { get { return _taskChain.Tasks; } <-- ERROR! You can't do this in C#! I want to return an IList<ITask> from an IList<IStates>. } } Assuming the IList returned will be read-only, I know that what I'm trying to achieve is safe (or is it not?). Is there any way I can accomplish what I'm trying? I wouldn't want to try to implement myself the TasksChain algorithm (again!), as it would be error prone and would lead to code duplication. Maybe I could just define an abstract Chain and then implement both TasksChain and StatesChain from there? Or maybe implementing a Chain<T> class? How would you approach this situation? The Details: I have defined an ITask interface: public interface ITask { bool Run(); ITask FailureTask { get; } } and a IState interface that inherits from ITask: public interface IState : ITask { IState FailureState { get; } } I have also defined an IHasTasksList interface: interface IHasTasksList { List<Tasks> Tasks { get; } } and an IHasStatesList: interface IHasTasksList { List<Tasks> States { get; } } Now, I have defined a TasksChain, that is a class that has some code logic that will manipulate a chain of tasks (beware that TasksChain is itself a kind of ITask!): class TasksChain : ITask, IHasTasksList { IList<ITask> tasks = new List<ITask>(); ... public List<ITask> Tasks { get { return _tasks; } } ... } I am implementing a State the following way: public class State : IState { private readonly TaskChain _taskChain = new TaskChain(); public State(Precondition precondition, Execution execution) { _taskChain.Tasks.Add(precondition); _taskChain.Tasks.Add(execution); } public bool Run() { return _taskChain.Run(); } public IState FailureState { get { return (IState)_taskChain.Tasks[0].FailureTask; } } ITask ITask.FailureTask { get { return FailureState; } } } which, as you can see, makes use of explicit interface implementations to "hide" FailureTask and instead show FailureState property. The problem comes from the fact that I also want to define a StatesChain, that inherits both from IState and IHasStateList (and that also imples ITask and IHasTaskList, implemented as explicit interfaces) and I want it to also hide IHasTaskList's Tasks and only show IHasStateList's States. (What is contained in "The problem" section should really be after this, but I thought puting it first would be way more reader friendly). (pff..long text) Thanks!

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  • How do I assert that two arbitrary type objects are equivalent, without requiring them to be equal?

    - by Tomas Lycken
    To accomplish this (but failing to do so) I'm reflecting over properties of an expected and actual object and making sure their values are equal. This works as expected as long as their properties are single objects, i.e. not lists, arrays, IEnumerable... If the property is a list of some sort, the test fails (on the Assert.AreEqual(...) inside the for loop). public void WithCorrectModel<TModelType>(TModelType expected, string error = "") where TModelType : class { var actual = _result.ViewData.Model as TModelType; Assert.IsNotNull(actual, error); Assert.IsInstanceOfType(actual, typeof(TModelType), error); foreach (var prop in typeof(TModelType).GetProperties()) { Assert.AreEqual(prop.GetValue(expected, null), prop.GetValue(actual, null), error); } } If dealing with a list property, I would get the expected results if I instead used CollectionAssert.AreEquivalent(...) but that requires me to cast to ICollection, which in turn requries me to know the type listed, which I don't (want to). It also requires me to know which properties are list types, which I don't know how to. So, how should I assert that two objects of an arbitrary type are equivalent? Note: I specifically don't want to require them to be equal, since one comes from my tested object and one is built in my test class to have something to compare with.

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  • VS2010 Implement Generic Interface expansion doesn't use specified type

    - by TJB
    Using the release version of Visual Studio 2010 I think there's a difference in the "Implement Interface" expansion from VS2008 If I speicify an interface and implement it in a class as so: public interface IRepository<T> where T : IModel { T Get<T>(int id); void Update<T>(); int Add<T>(T item); } public class MockRepository : IRepository<MockUser> { // ... } Then use the "Implement Interface" expansion and get this: public class MockRepository : IRepository<MockUser> { public T Get<T>(int id) { throw new NotImplementedException(); } public void Update<T>() { throw new NotImplementedException(); } public int Add<T>(T item) { throw new NotImplementedException(); } } Instead of what I expected public class MockRepository : IRepository<MockUser> { public MockUser Get<MockUser>(int id) { throw new NotImplementedException(); } public void Update<MockUser>() { throw new NotImplementedException(); } public int Add<MockUser>(MockUser item) { throw new NotImplementedException(); } } The IDE uses the type variable name from the generic interface definition T instead of the specified concrete type MockUser. Is this a bug? Or is something new just for VS2010 / .Net 4.0?

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  • Implementing IComparer<T> For IComparer<DictionaryEntry>

    - by Phil Sandler
    I am using the ObservableSortedDictionary from Dr. WPF. The constructor looks like this: public ObservableSortedDictionary(IComparer<DictionaryEntry> comparer) I am really struggling to create an implementation that satisfies the constructor and works. My current code (that won't compile) is: public class TimeCreatedComparer<T> : IComparer<T> { public int Compare(T x, T y) { var myclass1 = (IMyClass)((DictionaryEntry)x).Value; var myclass2 = (IMyClass)((DictionaryEntry)y).Value; return myclass1.TimeCreated.CompareTo(myclass2.TimeCreated); } } It says I can't cast from T to DictionaryEntry. If I cast directly to IMyClass, it compiles, but I get a runtime error saying I can't cast from DictionaryEntry to IMyClass. At runtime, x and y are instances of DictionaryEntry, which each have the correct IMyClass as their Value.

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