How does the const { None } example type-inference work? The size of the option type can't be known without knowing the type of the Somevariant.

Edit: aha, it doesn't work as-is. It needs to infer the type of elements of foo from usage. https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=05a95c592626b6935ae812527aa6bbc6

I don't understand what the advantages of const expressions are.

Isn't const { None } the same as just None?