Question

Imagine I have an interface that specifies some collection handler:

interface ICollectionHandler<T> where T : new() { ... }

I then have same other class that wants a collection handler, which it will use for various types, so I want to do something like:

class SomeClass<T> where T : ICollectionHandler<> ...

If I do this though, I get an error saying that the “Type argument is missing”.

So is there a way of specifying that T is a generic type, whose own type argument can be specified at runtime, or am I pushing C# beyond its (possibly sensible) boundaries here?

Answer 1

You can create a base interface for ICollectionHandler<T> and constrain against it.

interface ICollectionHandler { ... }
interface ICollectionHandler<T> : ICollectionHandler where T : new() { ... }
class SomeClass<T> where T : ICollectionHandler { ... }

Or add a parameter to SomeClass representing the Type that should be passed into the ICollectionHandler<T> constraint:

class SomeClass<T, U> where T : ICollectionHandler<U> { ... }