Question

I have a C# generic:

public class Generic<TParameter> { ... }

It does not appear that I can use unbound types as type parameters. I get error CS1031: Type expected when I try the following:

var lGenericInstance = new Generic<List<>>();

How can I use an unbound type as a generic type parameter? Are there workarounds? My generic class is just using reflection so I can get a list of the provided type’s members as strings.

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Update: My question about the unbound type has been answered, so I have followed up with a separate question that addresses my specific problem.

Answer 1

Try this:

class Foo<T> { }
class Bar<T> { }

Type unboundBar = typeof(Bar<>);
Type unboundFoo = typeof(Foo<>);
Type boundFoo = unboundFoo.MakeGenericType(new[] { unboundBar });
Console.WriteLine(boundFoo.Name);
Conosle.WriteLine(boundFoo.GetGenericArguments().First().Name);

Note that you can’t write

Type boundFoo = typeof(Foo<Bar<>>)

because the specification explicitly states:

An unbound generic type can only be used within a typeof-expression (§7.6.11).

(Bar<> is not being used as a parameter to the typeof-expression here, rather, it’s a generic type parameter to the parameter to a typeof-expression.)

However, it’s perfectly legal within the CLR, as the above using reflection shows.

But what are you trying to do? You can’t have instances of unbound types, so I don’t get it.