Thanks André, you’re absolutely right, I’ll correct that. To be honest, that entire section is pending the final release of the C# 9 compiler. There’s a fair bit of discrepancy between what was proposed, and subsequently accepted for C# 9 in the language repository, and what was shipped with the release candidates.
Thanks for pointing out this error. I’ve been drafting this article since the first features were accepted for C# 9, and some stuff that didn’t make the cut after all may still be in the article here and there. When C# 9 is released in full, I’ll go over all of the examples in this article once more and fix any discrepancies.