delegate Task<string> GetUserEmail(int userId);
This provides more guidance than taking in a: Func<int, Task<string>> getUserEmail
If you can annotate implementations of the delegate the tooling support becomes even nicer. Not all Funcs with the same shape have the same semantics, in my ideal C#-like language. delegate Task<string> GetEntityName(int id)
public async Task<string> MyEntityNameImpl(int id)
I'd love to be able to mark the method: public async Task<string> MyEntityNameImpl(int id) : GetEntityName
This could just be removed on compile but it would make the tooling experience much better in my view when you control the delegate implementations and definitions.