C# Invalid variance error when having an out method parameter

Asked Jan 24 '18 at 15:11

Active Jan 24 '18 at 15:11

Viewed 34 times

I have looked at similar questions, though my case seems to be different.

For this code:

public interface MyInterface<out T> {
  bool TrySomething(out T val);
}

I get this error on C# 7.2:

Invalid variance: The type parameter 'T' must be invariantly valid on 'MyInterface.TrySomething(out T)'. 'T' is covariant.

Is this a bug, or am I missing something? I am not supplying the T value here, I am getting it out (i.e. reading, hence the out method parameter modifier in TrySomething. So, why doesn't it compile?

asked Jan 24 '18 at 15:11

Fit Dev

3,413
3
30
54

2

No, a parameter goes _into_ the method, whether it's marked `out` or not. – CodeCaster Jan 24 '18 at 15:12
1

Thanks for pointing this out. I did not see the question you mentioned. – Fit Dev Jan 24 '18 at 15:16
No problem, hope it clears things up! – CodeCaster Jan 24 '18 at 15:18

C# Invalid variance error when having an out method parameter

0 Answers0