Cannot convert type 'System.Action' to 'System.Action

Question

I am wondering how I achieve something like this?

Action<int>  test = (val) => Console.WriteLine("I am " + val);
Action<object> test2 = (Action<object>) test;

code : https://dotnetfiddle.net/rZYvLZ

I need to do this because I am creating a class that will need to support many (thousands) of Actions delegate argument types

What would you expect to happen if you called `test2.Invoke(new object())`? Would you expect an `InvalidCastException`? Delegates are generally intended to be type-safe. If you provide more context, we may be able to help you more - at the moment this is an XY problem. — Jon Skeet, Apr 04 '18 at 07:03
Did you look for variance and covariance in C#? E.g. this post may help, although not specifically for `Action`: https://stackoverflow.com/questions/3528821/generics-and-casting-cannot-cast-inherited-class-to-base-class — MakePeaceGreatAgain, Apr 04 '18 at 07:05
Keep in mind (ignoring limited co- and contra- variance support) - just because two types `A` and `B` have a particular inheritance relationship, that *does not* means that a generic type closed over those types (`G` and `G`) exhibits the *same* inheritance relationship. In general (again, ignoring the limited variance support) there is *no* inheritance relationship between them. — Damien_The_Unbeliever, Apr 04 '18 at 07:09
Not very clear on what you want to achieve. Looks like you want to do function currying. `Action — Umang, Apr 04 '18 at 07:09
https://stackoverflow.com/questions/3444246/convert-actiont-to-actionobject — M Bakardzhiev, Apr 04 '18 at 07:10

score 4 · Accepted Answer · answered Apr 04 '18 at 07:03

Well, you could wrap the first action:

Action<object> test2 = (object o) => test((int)o);

But I think it doesn't need much explanation this is a very unsafe thing to do. So instead of breaking type safety, maybe you can come up with a better design that does respect type safety.

1 Answers1