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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • How to set -Xbootclasspath for a JRE with a custom launcher?

    - by Tom
    I have a Java application which is using a certain Java Runtime Environment. The application uses it's own launcher to startup the java virtual machine. No use of the java.exe, javaw.exe, javaws.exe binaries is being made -- as the application seems to have it's own launcher which is a different executable. This custom launcher is using the rest of the JRE files, such as bin/client/jvm.dll and rt.jar package etc. Now, the problem is that I want to set a boot class path for this custom launcher. The custom launcher does not support the -Xbootclasspath command line parameter, like the default java.exe does. Is there any way for me to set the boot class path now for this java runtime environment? Thanks in advance. Some things to keep in mind: I do not have the source of this application This is meant for self and personal debugging use only, not for distribution

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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 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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  • Reusable non generic method for generic methods

    - by Jehof
    I have the following base interface public interface IHandler{ void Handle(IMessage message); } and an generic interface inheriting the base interface public interface IHandler<TMessage> : IHandler where TMessage : IMessage{ void Handle(TMessage message); } My classes can implement the interface IHandler<TMessage> mutiple times. IMessage is an base interface for messages and isn´t relevant here. Currently i´m implementing the interfaces as follows. public class ExampleHandler : IHandler<ExampleMessage>, IHandler<OtherExampleMessag>{ void IHandler.Handle(IMessage message){ ExampleMessage example = message as ExampleMessage; if (example != null) { Handle(example); } else { OtherExampleMessage otherExample = message as OtherExampleMessage; if (otherExample != null) { Handle(otherExample); } } public void Handle(ExampleMessage) { //handle message; } public void Handle(OtherExampleMessage) { //handle message; } } What bothers me is the way i have to implement the Handle(IMessage) method, cause in my opinion its many redundant code, and i have to extend the method each time when i implement a new IHandler<TMessage> interface on my class. What i´m looking for is a more generic way to implement the Handle(IMessage) method (maybe in a base class for Handlers), but i´m currently stuck how to do that.

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  • Type-safe generic data structures in plain-old C?

    - by Bradford Larsen
    I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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  • Unit test approach for generic classes/methods

    - by Greg
    Hi, What's the recommended way to cover off unit testing of generic classes/methods? For example (referring to my example code below). Would it be a case of have 2 or 3 times the tests to cover testing the methods with a few different types of TKey, TNode classes? Or is just one class enough? public class TopologyBase<TKey, TNode, TRelationship> where TNode : NodeBase<TKey>, new() where TRelationship : RelationshipBase<TKey>, new() { // Properties public Dictionary<TKey, NodeBase<TKey>> Nodes { get; private set; } public List<RelationshipBase<TKey>> Relationships { get; private set; } // Constructors protected TopologyBase() { Nodes = new Dictionary<TKey, NodeBase<TKey>>(); Relationships = new List<RelationshipBase<TKey>>(); } // Methods public TNode CreateNode(TKey key) { var node = new TNode {Key = key}; Nodes.Add(node.Key, node); return node; } public void CreateRelationship(NodeBase<TKey> parent, NodeBase<TKey> child) { . . .

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  • F# compilation error: Unexpected type application

    - by Jim Burger
    In F#, given the following class: type Foo() = member this.Bar<'t> (arg0:string) = ignore() Why does the following compile: let f = new Foo() f.Bar<Int32> "string" While the following won't compile: let f = new Foo() "string" |> f.Bar<Int32> //The compiler returns the error: "Unexpected type application"

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  • How to make TObjectDictionary.Values accessible as property?

    - by Holgerwa
    I have an object like this: TMyObj = class private FObjList: TObjectDictionary <integer, TMyObject>; public constructor Create; destructor Destroy; // How to access Values correctly? Something similar to this not working code property Values: TValueCollection read FObjList.Values write FObjList.Values; end; var MyObj: TMyObj; To access the values of FObjList, I'd like to write: for tmpObject in MyObj.Values do ... How do I need to declare the property "Values" so that MyObj.Values behaves exactly as if I would access MyObj.FObjList.Values?

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  • c# template member functions

    - by user3730583
    How can I define a template member function in C# For instance I will fill any collection which supports an Add(...) member function, please check out the sample code below public class CInternalCollection { public static void ExternalCollectionTryOne<T<int>>(ref T<int> ext_col, int para_selection = 0) { foreach (int int_value in m_int_col) { if (int_value > para_selection) ext_col.Add(int_value); } } public static void ExternalCollectionTryTwo<T>(ref T ext_col, int para_selection = 0) { foreach (int int_value in m_int_col) { if (int_value > para_selection) ext_col.Add(int_value); } } static int[] m_int_col = { 0, -1, -3, 5, 7, -8 }; } The ExternalCollectionTryOne<...(...) would be the preferred kind, because the int type can be explicit defined, but results in an error: Type parameter declaration must be an identifier not a type The type or namespace name 'T' could not be found (are you missing a using directive or an assembly reference?) The ExternalCollectionTryTwo<...(...) results in an error: 'T' does not contain a definition for 'Add' and no extension method 'Add' accepting a first argument of type 'T' could be found (are you missing a using directive or an assembly reference?)... I hope the problem is clear – any suggestions? ----------------------------- edit -------------------------- The answers with the interface ICollection<.. without a template member works fine and thanks all for this hint, but I still cannot define successfully a member template(generic) function So a more simpler example ... how can I define this public class CAddCollectionValues { public static void AddInt<T>(ref T number, int selection) { T new_T = new T(); //this line is just an easy demonstration to get a compile error with type T foreach (int i_value in m_int_col) { if (i_value > selection) number += i_value; //again the type T cannot be used } } static int[] m_int_col = { 0, -1, -3, 5, 7, -8 }; }

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  • Visual Studio 2008 having problems with namespaces when used as type in Generic coolection

    - by patrick
    I just upgraded last week from Visual Studio 2005 to 2008. I am having an issue with compiler resolving namespaces when I use a class as a type in a Generic collection. Intellisense recognizes the class and the compiler generates no errors when I use the class except when it is a type in a Generic collection declaration either as return type for a Property or as a parameter to a method. This is happening in my only project that is targeting the 3.5 framework, but changing the project containing the class to use the 3.5 framework doesn't fix the problem. Examples Compile fine MyClass myClass = new MyClass(); SortedList <DateTime,MyClass> listOfClasses = new SortedList<DateTime,MyClass> Compile error - Namespace could not be found public SortedList<DateTime,MyClass> ClassList { get; set; } private void DoSomethingToLists(SortedList<DateTime,MyClass> classList) Intellisense has no problem resolving the namespace, only the compiler. Is this a known bug or am I missing something obvious? Will SP1 fix it? I was able to create a new library containing just this class targeting 3.5 and am now able to successfully use this in both 3.5 and 2.0 projects. My guess is that even though I tried to change the target of my original library, since it was still referencing 2.0 projects there was some conflict.

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  • Why can I derived from a templated/generic class based on that type in C# / C++

    - by stusmith
    Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

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  • Wouldn't it be nice to have a type variable referring to the class's instance.

    - by user93197
    I often have a pattern like this: class VectorBase<SubClass, Element> where SubClass : VectorBase<SubClass, Element>, new() where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(); result.data = newData; return result; } } class VectorInt : VectorBase<VectorInt, Int32> { } class MyInt : Addable<MyInt> { int data; public MyInt(int data) { this.data = data; } public MyInt add(MyInt t) { return new MyInt(data + t.data); } } interface Addable<T> { T add(T t); } But I would rather just have: class VectorBase2<Element> where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(data); return result; } } class VectorInt2 : VectorBase2<Int32> { } Why not make the subclass type available to all classes? Is this technically impossible?

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