Casting Action<string> to Action<object>

Question

I need to cast an Action<string> to Action<object>. While this is type-unsafe in general, in my case it will always be called with a string. I'm getting this error:

Unable to cast object of type 'System.Action1[System.String]' to type 'System.Action1[System.Object]'.

Any clues? Reflection is fair game. Wrapping the one delegate into another is not.

UPDATE: I created a new question at Creating an performant open delegate for an property setter or getter with a better explanation of my issue, and a solution using wrapping which I want to improve on

Answer 1

First, it's not safe. Something that can accept any string can't (necessarily) accept any object. Think of a example method:

void method(String s)
{
  s.Trim();
}

Obviously, this would fail if s were an object without Trim.

Technically, this means Action is contravariant on T. You could assign an Action<string> to a hypothetical Action<SubclassString> reference, but string can not be subclassed.

It's true that C# allows regular unsafe casts (e.g. object itself to string), at the risk of a InvalidCastException. However, they chose not to implement the infrastructure for unsafe delegate casts.

EDIT: I don't know of a way to do it without a wrapper.