Yeah, though, one annoyance with Nullable<T> in C# is that T must be a value type. That gets obnoxious when you want to program generically against it, because, e.g., you can't do have a method like

  TValue? TryGetValue<TKey, TValue>(TKey key)

and have it work with any possible TKey. Unless they've fixed this in the past couple years, you get stuck writing your own option type to be able to also work with reference types, which is always fun to try and get past code review, or you fall back on the out parameters idiom, which is not composable.

> Yeah, though, one annoyance with Nullable<T> in C# is that T must be a value type.

Unnecessary because class types already allow null. I would not be surprised if a method e.g. public Customer TryFindCustomer(int id); returns null if it can't find the customer.

Of course, if you want to return either a customer or an error details, then you need another type or generic wrapper.

Not strictly necessary, no. But the example I wrote was getting at was meant to point out that this bifurcation can make it harder to compose generic types. It's not really an ideal design decision for modern C# so much as a hold-over from the language's early years, when idiomatic usage favored a much more imperative style of programming.