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• Finding the specific type held in an ArrayList<Object> (ie. Object = String, etc.)

  - by Christopher Griffith

  Say I have an ArrayList that I have cast to an ArrayList of objects. I know that all the objects that were in the ArrayList I cast were of the same type, but not what the type was. Now, if the ArrayList is not empty, I could take one of the objects in it and use the instanceof operator to learn what the actual type is. But what of the case where the ArrayList is empty? How do I determine what type Object actually is then? Is it possible?

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• How to convet DataTable to List on runtype with out existin class property [closed]

  - by shamim

  Work on VS2010 C#,Have one DataTable ,want to convert this DataTable to List Suppose: Table dt; On run time want to create similar field from a datatable and fill fields in List.There is no existing class for list properties. ListName=TableName List property name=Table column name List Property type=Table column type List items=Table rows Note: Recently work on EF.To fullfill my project requirement, need to give flexibility to use to input and execute ESQL at runtime .I don’t want to put this execute result on datatable or List ,want to put this result on list. List has no existing class and property,don’t want to convert DataTable on list Type:DataRow If have any query please ask,Thanks in advanced.

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• Suggestions on Working with this Inherited Generic Method

  - by blu

  We have inherited a project that is a wrapper around a section of the core business model. There is one method that takes a generic, finds items matching that type from a member and then returns a list of that type. public List<T> GetFoos<T>() { List<IFoo> matches = Foos.FindAll( f => f.GetType() == typeof(T) ); List<T> resultList = new List<T>(); foreach (var match in matches) { resultList.Add((T)obj); } } Foos can hold the same object cast into various classes in inheritance hierarchy to aggregate totals differently for different UI presentations. There are 20+ different types of descendants that can be returned by GetFoos. The existing code basically has a big switch statement copied and pasted throughout the code. The code in each section calls GetFoos with its corresponding type. We are currently refactoring that into one consolidated area, but as we are doing that we are looking at other ways to work with this method. One thought was to use reflection to pass in the type, and that worked great until we realized the Invoke returned an object, and that it needed to be cast somehow to the List <T>. Another was to just use the switch statement until 4.0 and then use the dynamic language options. We welcome any alternate thoughts on how we can work with this method. I have left the code pretty brief, but if you'd like to know any additional details please just ask.

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• How to get all possible generic type in StructureMap?

  - by Soul_Master

  I just used StructureMap few days ago. I use StructureMap for collecting all validator class like the following code. public class BaseClassA {} public class ClassB : BaseClassA {} public class ClassC : BaseClassB {} public BaseClassAValidator : IValidator<BaseClassA>() {} In StructureMap, I only register IValidator interface for BaseClassAValidator class. But I want to get the same result when I call IValidator or IValidator that mean StructureMap should return IValidator where T is requested class or parent class of requested class. Is it possible? Or I need to manually call it.

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• (Action<T>).Name does not return expected values

  - by Tomas Lycken

  I have the following method (used to generate friendly error messages in unit tests): protected string MethodName<TTestedType>(Action<TTestedType> call) { return string.Format("{0}.{1}", typeof(TTestedType).FullName, call.Method.Name); } But when I call it as follows, I don't get the expected results: var nm = MethodName<MyController>(ctrl => ctrl.Create()); After running this code, nm contains "<Create_CreateShowsView>b__8", and not (as expected) "Create". How should I change the code to obtain the expected result?

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• Decrement all int values in Dictionary

  - by Jon

  I have a Dictionary<string,int> and I simply want to decrement the value in my dictionary by one. I have this but not sure if its best practice. foreach (KeyValuePair<string, int> i in EPCs) { EPCs[i.Key] = i.Value - 1; }

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• How to return a value based on the type of the generic T

  - by Blankman

  I have a method like: public T Get<T>(string key) { } Now say I want to return "hello" if the type is a string, and 110011 if it is type int. how can I do that? typeof(T) doesn't seem to work. I ideally want to do a switch statement, and return something based on the Type of the generic (string/int/long/etc). Is this possible?

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• How can I define a constructor in an open generic type?

  - by Cort

  I am trying to create on open generic type that has a constructor to be used by derived types, but I either don't know how to do it or it is not possible -- not sure which. public struct DataType<T> : IDataType { private T myValue; private TypeState myState; private DataType<T>(T initialValue, TypeState state) { myValue = initialValue; myState = state; } } Any help much appreciated! Cort

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• Generic collection class?

  - by Mark

  Is there anyway I can do this? class TSOC<TCollection, TValue> : ICollection<TValue>, INotifyCollectionChanged where TCollection : ICollection { private TCollection<TValue> collection; } It doesn't like my definition of collection. I'd prefer the definition to look like TSOC<TCollection> where the user can pass in List<int> or something, but then I need to pull out the "int" to know what interface to implement.

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• Using overloaded operator== in a generic function

  - by Dimitri C.

  Consider the following code: class CustomClass { public CustomClass(string value) { m_value = value; } public static bool operator==(CustomClass a, CustomClass b) { return a.m_value == b.m_value; } public static bool operator!=(CustomClass a, CustomClass b) { return a.m_value != b.m_value; } public override bool Equals(object o) { return m_value == (o as CustomClass).m_value; } public override int GetHashCode() { return 0; /* not needed */ } string m_value; } class G { public static bool enericFunction1<T>(T a1, T a2) where T : class { return a1.Equals(a2); } public static bool enericFunction2<T>(T a1, T a2) where T : class { return a1==a2; } } Now when I call both generic functions, one succeeds and one fails: var a = new CustomClass("same value"); var b = new CustomClass("same value"); Debug.Assert(G.enericFunction1(a, b)); // Succeeds Debug.Assert(G.enericFunction2(a, b)); // Fails Apparently, G.enericFunction2 executes the default operator== implementation instead of my override. Can anybody explain why this happens?

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• Generic factory of generic containers

  - by Feuermurmel

  I have a generic abstract class Factory<T> with a method createBoxedInstance() which returns instances of T created by implementations of createInstance() wrapped in the generic container Box<T>. abstract class Factory<T> { abstract T createInstance(); public final Box<T> createBoxedInstance() { return new Box<T>(createInstance()); } public final class Box<T> { public final T content; public Box(T content) { this.content = content; } } } At some points I need a container of type Box<S> where S is an ancestor of T. Is it possible to make createBoxedInstance() itself generic so that it will return instances of Box<S> where S is chosen by the caller? Sadly, defining the function as follows does not work as a type parameter cannot be declared using the super keyword, only used. public final <S super T> Box<S> createBoxedInstance() { return new Box<S>(createInstance()); } The only alternative I see, is to make all places that need an instance of Box<S> accept Box<? extends S> which makes the container's content member assignable to S. Is there some way around this without re-boxing the instances of T into containers of type Box<S>? (I know I could just cast the Box<T> to a Box<S> but I would feel very, very guilty.)

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• Generic object comparison diff routine

  - by MicMit

  The question stems from database tables comparison. Let's say we put left row in the instance Left and the right one into instance Right of the same type. And we'got many tables and respective types. How to implement more or less generic routine resulting in a collection of diffs e.g. propertyName , leftValue , rightValue for each such a pair of instances of the same type.

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• How to cast a list of inheriting objects to a collection of objects in Java ?

  - by Kartoch

  I've a collection type: Collection<A> collecA And I've a list in my object: List<B> listB Where B is extending A class B extends A { ... } But I can't do the following: collecA = listB I can't understand why since Collection is implemented by List.

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• How can I define multiple types with the same name and different type parameters using Reflection Em

  - by wawa

  How can I generate types like these using the System.Reflection.Emit libraries: public class Test<T> {} public class Test<T1, T2> {} When I call ModuleBuilder.DefineType(string) with the second type declaration, I get an exception because there is already another type in the module with the same name (I've already defined the type parameter on the first type). Any ideas?

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• java syntax why is it that way?

  - by yoavstr

  Why does this one does not work: ArrayList<LinkedList<int>> where this one does: ArrayList<LinkedList<Integer>> ???

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• Why does my WCF service return and ARRAY instead of a List <T> ?

  - by user193189

  In the web servce I say public List<Customer> GetCustomers() { PR1Entities dc = new PR1Entities(); var q = (from x in dc.Customers select x).ToList(); return q; } (customer is a entity object) Then I generate the proxy when I add the service.. and in the reference.cd it say public wcf1.ServiceReference1.Customer[] GetCustomers() { return base.Channel.GetCustomers(); } WHY IS IT AN ARRAY? I asked for a List. help.

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• What CLR do when compare T with null, and T is a struct?

  - by Fujiy

  private static void SaveOrRemove<T>(string key, T value) { if (value == null) { Console.WriteLine("Remove: " +key); } .... } If I call passing 0 to value: SaveOrRemove("MyKey", 0), the condition (value == null) is false, then CLR dont make a (value == default(T)). What really happens?

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• implict type cast in generic method

  - by bitbonk

  why do I get a compiler error in the following code stating: Cannot implicty convert type SpecialNode to T even though T must derive from NodeBase as I defined in the where clause and even though SpecialNode actually derived from NodeBase? public static T GetNode<T>() where T : NodeBase { if (typeof(T) == typeof(SpecialNode)) { return ThisStaticClass.MySpecialNode; // <-- compiler error } if (typeof(T) == typeof(OtherSpecialNode)) { return ThisStaticClass.MyOtherSpecialNode; // <-- compiler error } ... return default(T); }

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• Call Generic method using runtime type and cast return object

  - by markpirvine

  I'm using reflection to call a generic method with a type determined at runtime. My code is as follows: Type tType = Type.GetType(pLoadOut.Type); MethodInfo method = typeof(ApiSerialiseHelper).GetMethod("Deserialise", new Type[] { typeof(string) }); MethodInfo generic = method.MakeGenericMethod(tType); generic.Invoke(obj, new object[] { pLoadOut.Data }); This works ok. However the generic.Invoke method returns an object, but what I would like is the type determined at runtime. Is this possible with this approach, or is there a better option? Mark

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• Is it possible in Scala to force the caller to specify a type parameter for a polymorphic method ?

  - by Alex Kravets

  //API class Node class Person extends Node object Finder { def find[T <: Node](name: String): T = doFind(name).asInstanceOf[T] } //Call site (correct) val person = find[Person]("joe") //Call site (dies with a ClassCast inside b/c inferred type is Nothing) val person = find("joe") In the code above the client site "forgot" to specify the type parameter, as the API writer I want that to mean "just return Node". Is there any way to define a generic method (not a class) to achieve this (or equivalent). Note: using a manifest inside the implementation to do the cast if (manifest != scala.reflect.Manifest.Nothing) won't compile ... I have a nagging feeling that some Scala Wizard knows how to use Predef.<:< for this :-) Ideas ?

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• Generic type parameter naming convention for Java (with multiple chars)?

  - by chaper29

  In some interfaces i wrote I'd like to name generic type parameter with more than one character to make the code more readable. Something like.... Map<Key,Value> Instead of this... Map<K,V> But when it comes to methods, the type-parameters look like java-classes which is also confusing. public void put(Key key, Value value) This seems like Key and Value are classes. I found or thought of some notations, but nothing like a convention from sun or a general best-practice. Alternatives i guesed of or found... Map<KEY,VALUE> Map<TKey,TValue>

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• private static <T> T cloneX(T x) - What does the <T> signify here?

  - by java_geek

  In the above declaration, what is the for?

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• What is the best way to clone/deep copy a .NET generic Dictionary<string, T>?

  - by mikeymo

  I've got a generic dictionary Dictionary that I would like to essentially make a Clone() of ..any suggestions.

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• Generic Event Generator and Handler from User Supplied Types?

  - by JaredBroad

  I'm trying to allow the user to supply custom data and manage the data with custom types. The user's algorithm will get time synchronized events pushed into the event handlers they define. I'm not sure if this is possible but here's the "proof of concept" code I'd like to build. It doesn't detect T in the for loop: "The type or namespace name 'T' could not be found" class Program { static void Main(string[] args) { Algorithm algo = new Algorithm(); Dictionary<Type, string[]> userDataSources = new Dictionary<Type, string[]>(); // "User" adding custom type and data source for algorithm to consume userDataSources.Add(typeof(Weather), new string[] { "temperature data1", "temperature data2" }); for (int i = 0; i < 2; i++) { foreach (Type T in userDataSources.Keys) { string line = userDataSources[typeof(T)][i]; //Iterate over CSV data.. var userObj = new T(line); algo.OnData < typeof(T) > (userObj); } } } //User's algorithm pattern. interface IAlgorithm<TData> where TData : class { void OnData<TData>(TData data); } //User's algorithm. class Algorithm : IAlgorithm<Weather> { //Handle Custom User Data public void OnData<Weather>(Weather data) { Console.WriteLine(data.date.ToString()); Console.ReadKey(); } } //Example "user" custom type. public class Weather { public DateTime date = new DateTime(); public double temperature = 0; public Weather(string line) { Console.WriteLine("Initializing weather object with: " + line); date = DateTime.Now; temperature = -1; } } }

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• What is the best way to write class template-like generic code in C?

  - by Ribtoks

  I need to write AVL-tree with generic type in C. The best way I know is to use [ void* ] and to write some functions for creating, copying, assignment and destruction. Please, tell me some better way.

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