Support for Union type?

I have a project where we are simulating union types, by having a class where one, and only one, attribute can and must be set.

For instance (contrived example):

public record AgentUnion {
  public Monster? Monster {get; set;}
  public Player? Player {get; set;}
}
public record Monster {
  public int ArtificialIntelligenceLevel {get; set;}
}
public record Player {
  public List<string> BackpackContents {get; set;}
}

This allows a heterogenous list of either player or monster. It would have been great to have an annotation like [OneOf] or [Union] that requires the user to provide one, and only one, of those attributes.

And, yes, there is no good way of handling each one of these cases in C#, with a compiler check, and I’m not sure what that would look like.

I’m using:

if (agent.Monster != null){...
} else if (agent.Player != null){...
} else throw new Exception();

[jhf]

In the case of AnyOf then the type would be quite straightforward:

...
  public AnyOf<Monster,Player> Agent {get; set;}
...

I’m currently using ServiceStack.OrmLite so I would need that to understand the AnyOf as well.

The OneOf has the advantage that it checks for completeness at compile time.

[jhf]

@cezarypiatek I have been using OneOf, but I see that AnyOf has support for json as well!