CODEWITHSUNDEEP
c#genericsinterfacedelegates
Murat
Murat

Reputation: 803

Creating Generic Delegates with Generic Interface Arguments

I want to create a generic delegate. It will delegate functions that have generic types as parameter.

For example : I have an interface : 

public interface IProblemState<T> : IComparable<IProblemState<T>>, IEquatable<IProblemState<T>>
        where T : IEquatable<T>
{}

And I have two different class

public class Class1 : IEquatable<Class1>
{ }

public class Class2 : **IProblemState<Class1>**
{ }

And after I have an delegate 

public delegate SortedSet<IProblemState<T>> ExpanderDelegate<T>(IProblemState<T> currentState) 
        where T : IEquatable<T>;

I can NOT create a delegate with a function that have derived class parameter (Instance of Class 2).

For Example : 

SortedSet<**Class2**> expander(**Class2** currentState)
{}

ExpanderDelegate<Class2> expanderDel = new ExpanderDelegate(**expander**);

When I want to create delegate, I get below error.

No overload for 'expander' matches delegate 'ExpanderDelegate'

I want to use this delegate with all function that have derived parameters.

Is it possible with C#?

Thanks.

Upvotes: 0

Views: 612

Answers (1)

Kris Vandermotten
Kris Vandermotten

Reputation: 10201

Of course you cannot. The delegate says: give me a function that can take any IProblemState<T> as a parmeter, and you give it a function that can only take Class2.

What if there were a Class3 that also implements IProblemState<T>? Surely, the delegate signature says I should be able to pass an instance of Class3 in as a parameter. But the function wouldn't allow it (it only allows Class2 instances). That's why that function cannot be assigned to a variable of that delegate type.

What you can do, is use this generic delegate:

public delegate SortedSet<T> ExpanderDelegate<T,U>(T currentState) 
    where T : IProblemState<U> where U: IEquatable<U>;

Upvotes: 1

Related Questions