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  • Is there a way to achieve covariance of generic types in C# 3.5?

    - by nullDev
    This has been introduced in C# 4.0, but is there a way to achieve this in c# 3.5? For e.g., consider the following code: class Base { } class Derived1 : Base { } class Derived2 : Base { } class User<T> where T : Base { } class User1 : User<Derived1> { } Now, I would like to have a list of User<T>, in which I can store User<Derived1> as well as User<Derived2>, but the following code fails to compile in C# 3.5: List<User<Base>> users = new List<User<Base>>(); users.Add(new User1()); Any ideas?

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  • Java. Best procedure to de-serialize a Java generic object?

    - by Jake
    What is the best procedure for storing and retrieving, using native Java serialization, generic objects like ArrayList<String>? Edit: To clarify. When I serialize an object of type ArrayList<String> I'd like to de-serialize to the same type of object. However, I know of no way to cast back to this generic object without causing warnings.

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  • .NET generic 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 Any/Attach/Add function for Entity Framework

    - by Matt Thrower
    Looking through my EF classes, they're littered with code that looks like this: if (_myContext.[EntityType].Any(d => d.RowId == dc.RowId)) { _myContext.[EntityType].Attach(dc); _myContext.Entry(dc).State = EntityState.Modified; } else { _myContext.[EntityType].Add(dc); } It's the same thing over and over, and is clearly itching to be handled by a generic function. However, I'm not sure how you'd go about handling the need for it to deal with a variety of unexpected entity types. A good example to get me started would be most appreciated.

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  • Traversing through an arbitrary dictionary tree structure in C#

    - by Rudism
    I am trying to write a recursive C# function that will operate on generic dictionaries of the form IDictionary<string, T> where T is either another IDictionary<string, T> or a string. My first failed attempt looked something like this: public string HandleDict(IDictionary<string, string> dict){ // handle the leaf-node here } public string HandleDict<T>(IDictionary<string, IDictionary<string, T>> dict){ // loop through children foreach(string key in dict.Keys){ HandleDict(dict[key]); } } I also tried variants of HandleDict<T>(IDictionary<string, T>) where T : IDictionary<string, T> but that also doesn't quite work. I know that what I want to do could be achieved through a custom class as the parameter instead of dictionaries, and that my attempts are conceptually flawed (there's no end to the recursion in the generic function). I would still like to know if there is actually a way to do what I want here using just generic IDictionaries.

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  • Generic InBetween Function.

    - by Luiscencio
    I am tired of writing x > min && x < max so i wawnt to write a simple function but I am not sure if I am doing it right... actually I am not cuz I get an error: bool inBetween<T>(T x, T min, T max) where T:IComparable { return (x > min && x < max); } errors: Operator '>' cannot be applied to operands of type 'T' and 'T' Operator '<' cannot be applied to operands of type 'T' and 'T' may I have a bad understanding of the where part in the function declaring note: for those who are going to tell me that I will be writing more code than before... think on readability =) any help will be appreciated EDIT deleted cuz it was resolved =) ANOTHER EDIT so after some headache I came out with this (ummm) thing following @Jay Idea of extreme readability: public static class test { public static comparision Between<T>(this T a,T b) where T : IComparable { var ttt = new comparision(); ttt.init(a); ttt.result = a.CompareTo(b) > 0; return ttt; } public static bool And<T>(this comparision state, T c) where T : IComparable { return state.a.CompareTo(c) < 0 && state.result; } public class comparision { public IComparable a; public bool result; public void init<T>(T ia) where T : IComparable { a = ia; } } } now you can compare anything with extreme readability =) what do you think.. I am no performance guru so any tweaks are welcome

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  • Why is Delphi unable to infer the type for a parameter TEnumerable<T>?

    - by deepc
    Consider the following declaration of a generic utility class in Delphi 2010: TEnumerableUtils = class public class function InferenceTest<T>(Param: T): T; class function Count<T>(Enumerable: TEnumerable<T>): Integer; overload; class function Count<T>(Enumerable: TEnumerable<T>; Filter: TPredicate<T>): Integer; overload; end; Somehow the compiler type inference seems to have problems here: var I: Integer; L: TList<Integer>; begin TEnumerableUtils.InferenceTest(I); // no problem here TEnumerableUtils.Count(L); // does not compile: E2250 There is no overloaded version of 'Count' that can be called with these arguments TEnumerableUtils.Count<Integer>(L); // compiles fine end; The first call works as expected and T is correctly inferred as Integer. The second call does not work, unless I also add <Integer -- then it works, as can be seen in the third call. Am I doing something wrong or is the type inference in Delphi just not supporting this (I don't think it is a problem in Java which is why expected it to work in Delphi, too).

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  • Cast Object to Generic List

    - by CrazyJoe
    I have 3 generict type list. List<Contact> = new List<Contact>(); List<Address> = new List<Address>(); List<Document> = new List<Document>(); And save it on a variable with type object. Now i nedd do Cast Back to List to perfom a foreach, some like this: List<Contact> = (List<Contact>)obj; But obj content change every time, and i have some like this: List<???> = (List<???>)obj; I have another variable holding current obj Type: Type t = typeof(obj); Can i do some thing like that??: List<t> = (List<t>)obj; Obs: I no the current type in the list but i need to cast , and i dont now another form instead: List<Contact> = new List<Contact>(); Help Plz!!!

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  • 'Lexical' scoping of type parameters in C#

    - by leppie
    I have 2 scenarios. This fails: class F<X> { public X X { get; set; } } error CS0102: The type 'F' already contains a definition for 'X' This works: class F<X> { class G { public X X { get; set; } } } The only logical explanation is that in the second snippet the type parameter X is out of scope, which is not true... Why should a type parameter affect my definitions in a type? IMO, for consistency, either both should work or neither should work. Any other ideas? PS: I call it 'lexical', but it probably is not not the correct term.

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  • Constraint Validation

    - by tanuja
    I am using javax.validation.Validator and relevant classes for annotation based validation. Configuration<?> configuration = Validation.byDefaultProvider().configure(); ValidatorFactory factory = configuration.buildValidatorFactory(); Validator validator = factory.getValidator(); Set<ConstraintViolation<ValidatableObject>> constraintViolations = validator.validate(o); for (ConstraintViolation<ValidatableObject> value : constraintViolations) { List< Class< ? extends ConstraintValidator< ? extends Annotation,?>>> list = value.getConstraintDescriptor().getConstraintValidatorClasses(); } I get a compilation error stating: Type mismatch: cannot convert from List< Class< ? extends ConstraintValidator< capture#4-of ?,? to List< Class< ? extends ConstraintValidator< ? extends Annotation,? What am I missing?

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  • How to create a generic C free function .

    - by nomemory
    I have some C structures related to a 'list' data structure. They look like this. struct nmlist_element_s { void *data; struct nmlist_element_s *next; }; typedef struct nmlist_element_s nmlist_element; struct nmlist_s { void (*destructor)(void *data); int (*cmp)(const void *e1, const void *e2); unsigned int size; nmlist_element *head; nmlist_element *tail; }; typedef struct nmlist_s nmlist; This way I can have different data types being hold in "nmlist_element-data" . The "constructor" (in terms of OOP) has the following signature: nmlist *nmlist_alloc(void (*destructor)(void *data)); Where "destructor" is specific function that de-allocated "data" (being hold by the nmlist_element). If I want to have a list containing integers as data, my "destructor" would like this: void int_destructor(void *data) { free((int*)data); } Still i find it rather "unfriendly" for me to write a destructor functions for every simple primitive data type. So is there a trick to write something like this ? (for primitives): void "x"_destructor(void *data, "x") { free(("x" *)data); } PS: I am not a macro fan myself, and in my short experience regarding C, i don't use them, unless necessary.

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  • Cannot call action method 'System.Web.Mvc.PartialViewResult Foo[T](T)' on controller 'Controller' be

    - by MedicineMan
    Cannot call action method 'System.Web.Mvc.PartialViewResult FooT' on controller 'Controller' because the action method is a generic method <% Html.RenderAction("Foo", model = Model}); %> Is there a workaround for this limitation on ASP MVC 2? I would really prefer to use a generic. The workaround that I have come up with is to change the model type to be an object. It works, but is not preferred: public PartialViewResult Foo<T>(T model) where T : class { // do stuff }

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  • Why calling ISet<dynamic>.Contains() compiles, but throws an exception at runtime?

    - by Andrey Breslav
    Please, help me to explain the following behavior: dynamic d = 1; ISet<dynamic> s = new HashSet<dynamic>(); s.Contains(d); The code compiles with no errors/warnings, but at the last line I get the following exception: Unhandled Exception: Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'System.Collections.Generic.ISet<object>' does not contain a definition for 'Contains' at CallSite.Target(Closure , CallSite , ISet`1 , Object ) at System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid2[T0,T1](CallSite site, T0 arg0, T1 arg1) at FormulaToSimulation.Program.Main(String[] args) in As far as I can tell, this is related to dynamic overload resolution, but the strange things are (1) If the type of s is HashSet<dynamic>, no exception occurs. (2) If I use a non-generic interface with a method accepting a dynamic argument, no exception occurs. Thus, it looks like this problem is related particularly with generic interfaces, but I could not find out what exactly causes the problem. Is it a bug in the compiler/typesystem, or legitimate behavior?

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  • What would be different in Java if Enum declaration didn't have the recursive part

    - by atamur
    Please see http://stackoverflow.com/questions/211143/java-enum-definition and http://stackoverflow.com/questions/3061759/why-in-java-enum-is-declared-as-enume-extends-enume for general discussion. Here I would like to learn what exactly would be broken (not typesafe anymore, or requiring additional casts etc) if Enum class was defined as public class Enum<E extends Enum> I'm using this code for testing my ideas: interface MyComparable<T> { int myCompare(T o); } class MyEnum<E extends MyEnum> implements MyComparable<E> { public int myCompare(E o) { return -1; } } class FirstEnum extends MyEnum<FirstEnum> {} class SecondEnum extends MyEnum<SecondEnum> {} With it I wasn't able to find any benefits in this exact case. PS. the fact that I'm not allowed to do class ThirdEnum extends MyEnum<SecondEnum> {} when MyEnum is defined with recursion is a) not relevant, because with real enums you are not allowed to do that just because you can't extend enum yourself b) not true - pls try it in a compiler and see that it in fact is able to compile w/o any errors PPS. I'm more and more inclined to believe that the correct answer here would be "nothing would change if you remove the recursive part" - but I just can't believe that.

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  • How to Work Around Limitations in Generic Type Constraints in C#?

    - by Jose
    Okay I'm looking for some input, I'm pretty sure this is not currently supported in .NET 3.5 but here goes. I want to require a generic type passed into my class to have a constructor like this: new(IDictionary<string,object>) so the class would look like this public MyClass<T> where T : new(IDictionary<string,object>) { T CreateObject(IDictionary<string,object> values) { return new T(values); } } But the compiler doesn't support this, it doesn't really know what I'm asking. Some of you might ask, why do you want to do this? Well I'm working on a pet project of an ORM so I get values from the DB and then create the object and load the values. I thought it would be cleaner to allow the object just create itself with the values I give it. As far as I can tell I have two options: 1) Use reflection(which I'm trying to avoid) to grab the PropertyInfo[] array and then use that to load the values. 2) require T to support an interface like so: public interface ILoadValues { void LoadValues(IDictionary values); } and then do this public MyClass<T> where T:new(),ILoadValues { T CreateObject(IDictionary<string,object> values) { T obj = new T(); obj.LoadValues(values); return obj; } } The problem I have with the interface I guess is philosophical, I don't really want to expose a public method for people to load the values. Using the constructor the idea was that if I had an object like this namespace DataSource.Data { public class User { protected internal User(IDictionary<string,object> values) { //Initialize } } } As long as the MyClass<T> was in the same assembly the constructor would be available. I personally think that the Type constraint in my opinion should ask (Do I have access to this constructor? I do, great!) Anyways any input is welcome.

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  • Generic extension method returning IEnumerable<T> without using reflection

    - by roosteronacid
    Consider this snippet of code: public static class MatchCollectionExtensions { public static IEnumerable<T> AsEnumerable<T>(this MatchCollection mc) { return new T[mc.Count]; } } And this class: public class Ingredient { public String Name { get; set; } } Is there any way to magically transform a MatchCollection object to a collection of Ingredient? The use-case would look something like this: var matches = new Regex("([a-z])+,?").Matches("tomato,potato,carrot"); var ingredients = matches.AsEnumerable<Ingredient>();

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  • How to extend this design for a generic converter in java?

    - by Jay
    Here is a small currency converter piece of code: public enum CurrencyType { DOLLAR(1), POUND(1.2), RUPEE(.25); private CurrencyType(double factor) { this.factor = factor; } private double factor; public double getFactor() { return factor; } } public class Currency { public Currency(double value, CurrencyType type) { this.value = value; this.type = type; } private CurrencyType type; private double value; public CurrencyType getCurrencyType() { return type; } public double getCurrencyValue() { return value; } public void setCurrenctyValue(double value){ this.value = value; } } public class CurrencyConversion { public static Currency convert(Currency c1, Currency c2) throws Exception { if (c1 != null && c2 != null) { c2.setCurrenctyValue(c1.getCurrencyValue() * c1.getCurrencyType().getFactor() * c2.getCurrencyType().getFactor()); return c2; } else throw new Exception(); } } I would like to improve this code to make it work for different units of conversion, for example: kgs to pounds, miles to kms, etc etc. Something that looks like this: public class ConversionManager<T extends Convertible> { public T convert(T c1, T c2) { //return null; } } Appreciate your ideas and suggestions.

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  • [C#] Problems with implementing generic IEnumerator and IComparable

    - by r0h
    Hi all! I'm working on an AVL Tree. The tree itself seems to be working but I need a iterator to walk through the values of the tree. Therefore I tried to implement the IEnumerator interace. Unfortunately I get a compile time error implementing IEnumerator and IComparable. First the code and below that the error. class AvlTreePreOrderEnumerator<T> : IEnumerator<T> where T :IComparable<T> { private AvlTreeNode<T> current = default(T); private AvlTreeNode<T> tree = null; private Queue<AvlTreeNode<T>> traverseQueue = null; public AvlTreePreOrderEnumerator(AvlTreeNode<T> tree) { this.tree = tree; //Build queue traverseQueue = new Queue<AvlTreeNode<T>>(); visitNode(this.tree.Root); } private void visitNode(AvlTreeNode<T> node) { if (node == null) return; else { traverseQueue.Enqueue(node); visitNode(node.LeftChild); visitNode(node.RightChild); } } public T Current { get { return current.Value; } } object IEnumerator.Current { get { return Current; } } public void Dispose() { current = null; tree = null; } public void Reset() { current = null; } public bool MoveNext() { if (traverseQueue.Count > 0) current = traverseQueue.Dequeue(); else current = null; return (current != null); } } The error given by VS2008: Error 1 The type 'T' cannot be used as type parameter 'T' in the generic type or method 'Opdr2_AvlTreeTest_Final.AvlTreeNode'. There is no boxing conversion or type parameter conversion from 'T' to 'System.IComparable'. For now I've not included the tree and node logic. I anybody thinks is necessary to resolve this probleem, just say so! Thx!

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  • How do I configure StructureMap to use a generic repository?

    - by simonjreid
    I have an interface IGenericRepository<TEntity> where TEntity : IEntity and an implementation GenericRepository<TEntity> where TEntity : Entity. I'm trying to inject a specific IGenericRepository<Section> into a class using StructureMap: ObjectFactory.Initialize(x => { x.For(typeof(IGenericRepository<>)).Use(typeof(GenericRepository<>)); }); But when I try to use ObjectFactory.GetInstance<IGenericRepository<Section>>(); I get: StructureMap Exception Code: 202 No Default Instance defined for PluginFamily System.Data.Common.DbConnection Any ideas why this is or what I'm doing wrong? Thanks in advance, Simon

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  • Generic Type constraint in .net

    - by Jose
    Okay I'm looking for some input, I'm pretty sure this is not currently supported in .NET 3.5 but here goes. I want to require a generic type passed into my class to have a constructor like this: new(IDictionary<string,object>) so the class would look like this public MyClass<T> where T : new(IDictionary<string,object>) { T CreateObject(IDictionary<string,object> values) { return new T(values); } } But the compiler doesn't support this, it doesn't really know what I'm asking. Some of you might ask, why do you want to do this? Well I'm working on a pet project of an ORM so I get values from the DB and then create the object and load the values. I thought it would be cleaner to allow the object just create itself with the values I give it. As far as I can tell I have two options: 1) Use reflection(which I'm trying to avoid) to grab the PropertyInfo[] array and then use that to load the values. 2) require T to support an interface like so: public interface ILoadValues { void LoadValues(IDictionary values); } and then do this public MyClass<T> where T:new(),ILoadValues { T CreateObject(IDictionary<string,object> values) { T obj = new T(); obj.LoadValues(values); return obj; } } The problem I have with the interface I guess is philosophical, I don't really want to expose a public method for people to load the values. Using the constructor the idea was that if I had an object like this namespace DataSource.Data { public class User { protected internal User(IDictionary<string,object> values) { //Initialize } } } As long as the MyClass<T> was in the same assembly the constructor would be available. I personally think that the Type constraint in my opinion should ask (Do I have access to this constructor? I do, great!) Anyways any input is welcome.

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  • Generic cast type to primitive.

    - by Nix
    Is there a way to do the below? Imagine a generic result wrapper class. Where you have a type and an associated error list. When there is no result to return to the user we will use boolean to indicate success failure. I want to create a constructor that takes in an error list, and if the list is null or count 0, AND the type is a bool/Boolean i want to set it to true.... Seemingly simple, but amazingly not possible. public class Result<T>{ private T valueObject { get;set;} private List<Error> errors{ get;set;} public Result(T valueObj, List<Error> errorList){ this.valueObject = valueObj; this.errors = errorList; } public Result(List<Error> errors) { this.valueObject = default(ReturnType); if (valueObject is Boolean) { //Wont work compile //(valueObject as Boolean) = ((errors == null) || errors.Count == 0); //Compiles but detaches reference //bool temp = ((bool)(valueObject as object)) ; //temp = ((errors == null) || errors.Count == 0); } this.errors = errors; } } } Am I missing something simple? And in general I would prefer to do it without reflection.

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