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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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  • How to specify generic method type parameters partly

    - by DNNX
    I have an extension method like below: public static T GetValueAs<T, R>(this IDictionary<string, R> dictionary, string fieldName) where T : R { R value; if (!dictionary.TryGetValue(fieldName, out value)) return default(T); return (T)value; } Currently, I can use it in the following way: var dictionary = new Dictionary<string, object(); //... var list = dictionary.GetValueAs<List<int, object("A"); // this may throw ClassCastException - this is expected behavior; It works pretty fine, but the second type parameter is really annoying. Is it possible in C# 4.0 rewrite GetValueAs is such a way that the method will still be applicable to different types of string-keyed dictionaries AND there will be no need to specify second type parameter in the calling code, i.e. use var list = dictionary.GetValueAs<List<int("A"); or at least something like var list = dictionary.GetValueAs<List<int, ?("A"); instead of var list = dictionary.GetValueAs<List<int, object("A");

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  • Exporting to CSV with dynamic field type handling

    - by serhio
    I have to do an export from DB to CSV. field; fileld; field... etc Have 3 types of fields: Alpha, Numeric and Bool respresented as "alphaValue",intValue and True/False. I try to encapsulate this in a fields collection, in order to export if alpha then set "", if Bool=True/False if numeric let as is. and try to build a CsvField class: Public Structure?Class CsvField(Of T As ???) End Structure Enum FieldType Alpha Bool Numeric End Enum any suggestions welcomed.

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  • How can I make this code more generic

    - by Greg
    Hi How could I make this code more generic in the sense that the Dictionary key could be a different type, depending on what the user of the library wanted to implement? For example someone might what to use the extension methods/interfaces in a case where there "unique key" so to speak for Node is actually an "int" not a "string" for example. public interface ITopology { Dictionary<string, INode> Nodes { get; set; } } public static class TopologyExtns { public static void AddNode(this ITopology topIf, INode node) { topIf.Nodes.Add(node.Name, node); } public static INode FindNode(this ITopology topIf, string searchStr) { return topIf.Nodes[searchStr]; } } public class TopologyImp : ITopology { public Dictionary<string, INode> Nodes { get; set; } public TopologyImp() { Nodes = new Dictionary<string, INode>(); } }

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  • [VB.Net] Typecasting generic parameters.

    - by CFP
    Hello world! Using the following code: Function GetSetting(Of T)(ByVal SettingName As String, ByRef DefaultVal As T) As T Return If(Configuration.ContainsKey(SettingName), CType(Configuration(SettingName), T), DefaultVal) End Function Yields the following error: Value of type 'String' cannot be converted to 'T'. Any way I could specify that in all cases, the conversion will indeed be possible (I'm basically getting integers, booleans, doubles and strings). Thanks!

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  • c# Why can't open generic types be passed as parameters?

    - by Rich Oliver
    Why can't open generic types be passed as parameters. I frequently have classes like: public class Example<T> where T: BaseClass { public int a {get; set;} public List<T> mylist {get; set;} } Lets say BaseClass is as follows; public BaseClass { public int num; } I then want a method of say: public int MyArbitarySumMethod(Example example)//This won't compile Example not closed { int sum = 0; foreach(BaseClass i in example.myList)//myList being infered as an IEnumerable sum += i.num; sum = sum * example.a; return sum; } I then have to write an interface just to pass this one class as a parameter as follows: public interface IExample { public int a {get; set;} public IEnumerable<BaseClass> myIEnum {get;} } The generic class then has to be modified to: public class Example<T>: IExample where T: BaseClass { public int a {get; set;} public List<T> mylist {get; set;} public IEnumerable<BaseClass> myIEnum {get {return myList;} } } That's a lot of ceremony for what I would have thought the compiler could infer. Even if something can't be changed I find it psychologically very helpful if I know the reasons / justifications for the absence of Syntax short cuts.

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  • Convert IDictionary to Dictionary

    - by croisharp
    I have to convert System.Collections.Generic.IDictionary<string, decimal> to System.Collections.Generic.Dictionary<string, decimal>, and i can't. I tried the ToDictionary method and can't specify right arguments. I've tried the following: // my dictionary is PlannedSurfaces (of type IDictionary<string, decimal>) blabla.ToDictionary<string, decimal>(localConstruction.PlannedSurfaces)

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  • Create instance of generic type in Java?

    - by David Citron
    Is it possible to create an instance of a generic type in Java? I'm thinking based on what I've seen that the answer is "no" (due to type erasure), but I'd be interested if anyone can see something I'm missing: class SomeContainer<E> { E createContents() { return what??? } } EDIT: It turns out that Super Type Tokens could be used to resolve my issue, but it requires a lot of reflection-based code, as some of the answers below have indicated. I'll leave this open for a little while to see if anyone comes up with anything dramatically different than Ian Robertson's Artima Article.

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  • Creating parameterized type object using annonymous class

    - by Andrei Fierbinteanu
    This might be a stupid question, but I just saw a question asking how to create a Type variable for a generic type. The consensus seemed to be that you should have a dummy method returning that type, and then use reflection to get it (in this case he wanted Map<String, String>). Something like this : public Map<String, String> dummy() { throw new Error(); } Type mapStringString = Class.forName("ThisClass").getMethod("dummy").getGenericReturnType(); My question is, not having used reflection that much, couldn't you just do something like: Type mapStringString = new ParameterizedType() { public Type getRawType() { return Map.class; } public Type getOwnerType() { return null; } public Type[] getActualTypeArguments() { return new Type[] { String.class, String.class }; } }; Would this work? If not, why not? And what are some of the dangers/problems if it does (besides being able to return some Type like Integer<String> which is obviously not possible.

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  • understanding syb boilerplate elimination

    - by Pradeep
    In the example given in http://web.archive.org/web/20080622204226/http://www.cs.vu.nl/boilerplate/ -- Increase salary by percentage increase :: Float -> Company -> Company increase k = everywhere (mkT (incS k)) -- "interesting" code for increase incS :: Float -> Salary -> Salary incS k (S s) = S (s * (1+k)) how come increase function compiles without binding anything for the first Company mentioned in its type signature. Is it something like assigning to a partial function? Why is it done like that?

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  • C# - Why can't I enforce derived classes to have parameterless constructors?

    - by FrisbeeBen
    I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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  • C# Generic List constructor gives me a MethodAccessException

    - by evilfred
    Hi, I make a list in my code like so: List<IConnection> connections = new List<IConnection>(); where IConnection is my own interface. This is in a .NET 2.0 executable. If I run the code on my machine (with lots of .Net versions installed) it works fine. If I run it on my test machine (which only has .NET 3.5 SP1 installed) then I get a MethodAccessException in the System.Collections.Generic.List constructor. Any ideas what could be going wrong?

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  • is there some lightweight tecnique for adding type safety to identifier properties?

    - by shoren
    After using C++ I got used to the concept of Identifier which can be used with a class for the type, provides type safety and has no runtime overhead (the actual size is the size of the primitive). I want to do something like that, so I will not make mistakes like: personDao.find(book.getId());//I want compilation to fail personDao.find(book.getOwnerId());//I want compilation to succeed Possible solutuions that I don't like: For every entity have an entity id class wrapping the id primitive. I don't like the code bloat. Create a generic Identifier class. Code like this will not compile: void foo(Identifier book); void foo(Identifier person); Does anyone know of a better way? Is there a library with a utility such as this? Is implementing this an overkill? And the best of all, can this be done in Java without the object overhead like in C++?

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  • Map inheritance from generic class in Linq To SQL

    - by Ksenia Mukhortova
    Hi everyone, I'm trying to map my inheritance hierarchy to DB using Linq to SQL: Inheritance is like this, classes are POCO, without any LINQ to SQL attributes: public interface IStage { ... } public abstract class SimpleStage<T> : IStage where T : Process { ... } public class ConcreteStage : SimpleStage<ConcreteProcess> { ... } Here is the mapping: <Database Name="NNN" xmlns="http://schemas.microsoft.com/linqtosql/mapping/2007"> <Table Name="dbo.Stage" Member="Stage"> <Type Name="BusinessLogic.Domain.IStage"> <Column Name="ID" Member="ID" DbType="Int NOT NULL IDENTITY" IsPrimaryKey="true" IsDbGenerated="true" AutoSync="OnInsert" /> <Column Name="StageType" Member="StageType" IsDiscriminator="true" /> <Type Name="BusinessLogic.Domain.SimpleStage" IsInheritanceDefault="true"> <Type Name="BusinessLogic.Domain.ConcreteStage" IsInheritanceDefault="true" InheritanceCode="1"/> </Type> </Type> </Table> </Database> In the runtime I get error: System.InvalidOperationException was unhandled Message="Mapping Problem: Cannot find runtime type for type mapping 'BusinessLogic.Domain.SimpleStage'." Neither specifying SimpleStage, nor SimpleStage<T> in mapping file helps - runtime keeps producing different types of errors. DC is created like this: StreamReader sr = new StreamReader(@"MappingFile.map"); XmlMappingSource mapping = XmlMappingSource.FromStream(sr.BaseStream); DataContext dc = new DataContext(@"connection string", mapping); If Linq to SQL doesn't support this, could you, please, advise some other ORM, which does. Thanks in advance, Regards! Ksenia

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  • Compile time error: cannot convert from specific type to a generic type

    - by Water Cooler v2
    I get a compile time error with the following relevant code snippet at the line that calls NotifyObservers in the if construct. public class ExternalSystem<TEmployee, TEventArgs> : ISubject<TEventArgs> where TEmployee : Employee where TEventArgs : EmployeeEventArgs { protected List<IObserver<TEventArgs>> _observers = null; protected List<TEmployee> _employees = null; public virtual void AddNewEmployee(TEmployee employee) { if (_employees.Contains(employee) == false) { _employees.Add(employee); string message = FormatMessage("New {0} hired.", employee); if (employee is Executive) NotifyObservers(new ExecutiveEventArgs { e = employee, msg = message }); else if (employee is BuildingSecurity) NotifyObservers(new BuildingSecurityEventArgs { e = employee, msg = message }); } } public void NotifyObservers(TEventArgs args) { foreach (IObserver<TEventArgs> observer in _observers) observer.EmployeeEventHandler(this, args); } } The error I receive is: The best overloaded method match for 'ExternalSystem.NotifyObservers(TEventArgs)' has some invalid arguments. Cannot convert from 'ExecutiveEventArgs' to 'TEventArgs'. I am compiling this in C# 3.0 using Visual Studio 2008 Express Edition.

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  • Can i use a generic implicit or explicit operator? C#

    - by acidzombie24
    How do i change the following statement so it accepts any type instead of long? Now here is the catch, if there is no constructor i dont want it compiling. So if theres a constructor for string, long and double but no bool how do i have this one line work for all of these support types? ATM i just copied pasted it but i wouldnt like doing that if i had 20types (as trivial as the task may be) public static explicit operator MyClass(long v) { return new MyClass(v); }

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  • How to convert value of Generic Type Argument to a concrete type?

    - by Aleksey Bieneman
    I am trying to convert the value of the generic type parameter T value into integer after making sure that T is in fact integer: public class Test { void DoSomething<T>(T value) { var type = typeof(T); if (type == typeof(int)) { int x = (int)value; // Error 167 Cannot convert type 'T' to 'int' int y = (int)(object)value; // works though boxing and unboxing } } } Although it works through boxing and unboxing, this is an additional performance overhead and i was wandering if there's a way to do it directly. Thank you!

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  • removing items from a generic List<t>

    - by frosty
    I have the following method, I wish to remove items from my collection that match the product Id. Seems fairly straight forward, but i get an exception. Basically my collection is getting out of sync. So what is the best way to remove an item from a collection. public void RemoveOrderItem(Model.Order currentOrder, int productId) { foreach (var orderItem in currentOrder.OrderItems) { if (orderItem.Product.Id == productId) { currentOrder.OrderItems.Remove(orderItem); } } } Exception Details: System.InvalidOperationException: Collection was modified; enumeration operation may not execute

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  • Convert Text with newlines to a List<String>

    - by Vaccano
    I need a way to take a list of numbers in string form to a List object. Here is an example: string ids = "10\r\n11\r\n12\r\n13\r\n14\r\n15\r\n16\r\n17\r\n18\r\n19"; List<String> idList = new List<String>(); idList.SomeCoolMethodToParseTheText(ids); <------+ | foreach (string id in idList) | { | // Do stuff with each id. | } | | // This is the Method that I need ----------------+ Is there something in the .net library so that I don't have to write the SomeCoolMethodToParseTheText myself?

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  • How to find the class object of Java generic type?

    - by Samuel Yung
    Assume I have a generic type P which is an Enum, that is <P extends Enum<P>>, and I want to get the Enum value from a string, for example: String foo = "foo"; P fooEnum = Enum.valueOf(P.class, foo); This will get a compile error because P.class is invalid. So what can I do in order to make the above code work?

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  • How do I make lambda functions generic in Scala?

    - by Electric Coffee
    As most of you probably know you can define functions in 2 ways in scala, there's the 'def' method and the lambda method... making the 'def' kind generic is fairly straight forward def someFunc[T](a: T) { // insert body here what I'm having trouble with here is how to make the following generic: val someFunc = (a: Int) => // insert body here of course right now a is an integer, but what would I need to do to make it generic? val someFunc[T] = (a: T) => doesn't work, neither does val someFunc = [T](a: T) => Is it even possible to make them generic, or should I just stick to the 'def' variant?

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