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c#.netgenericscurrying

Does .Net support curried generics?

Suppose we have a nested generic class:

public class A<T> {
    public class B<U> { }
}

Here, typeof(A<int>.B<>) is in essence a generic class with two parameters where only the first is bound.

If I have a single class with two parameters

public class AB<T, U> { }

Is there a way to refer to "AB with T=int and U staying open"? If not, is this a C# limitation, or a CLR limitation?

Solution

  • Apparently it can't be done in C#, you have to specify either both type parameters, or none.

    And it doesn't seem to be supported by the CLR either, A<int>.B<> and A<string>.B<> refer to the same type:

    Type t1 = typeof(A<int>).GetNestedType("B`1");
Type t2 = typeof(A<string>).GetNestedType("B`1");
// t1.Equals(t2) is true

    The enclosing type of both types is A<> (open generic type)

    EDIT: further testing shows that typeof(A<int>.B<string>) is actually a generic type of arity 2, not a nested generic type of arity 1... typeof(A<int>.B<string>).GetGenericArguments() returns an array with typeof(int) and typeof(string). So typeof(A<int>.B<>) would actually be equivalent to (A.B)<int, >, which isn't supported (a generic type can't be partially closed)