The extra edge beyond not needing boxing is from niches, if T doesn't occupy all possible bit representations Rust will squeeze None into one of the unused bit values. Several standard library types have such niches, but today there is no stable way to make your own yet.

Which in the Rust world probably just needs to be one byte, probably a bit in most cases, in a register for state.

I don't think Java will be that optimized with value types. Even if the heap allocation is gone, there's still probably going to be a sizable object header?

In the interest of full and strict accuracy: see the enum’s full definition at https://github.com/rust-lang/rust/blob/d610b0c514b9ccb0dad5d.... There are a few points of specialness about Option that you can’t use elsewhere:

• #[rustc_diagnostic_item = "Option"]: the compiler knows about Option for the purpose of improving its error messages. I’m not sure how this is used, and am not looking it up now.

• #[lang = "None"] and #[lang = "Some"]: lang items allow the compiler to hook things up, like knowing the + operator maps to the core::ops::Add trait. https://github.com/search?q=repo%3Arust-lang%2Frust+%28optio... suggests that these lang items are only being used by Clippy, to provide better diagnostics. So if you use your own Option type, you won’t get Clippy lints related to Option.

• I suppose there are also the #[stable] attributes, which can’t be used outside the standard library, and which cause visible changes in generated documentation. When talking about strict accuracy, I guess that counts!

Anyway: for practical purposes this is just minor diagnostics and documentation stuff, not actual functionality, about which there is nothing special.

Since you mentioned the try operator, might as well look at the trait implementations on Option too, https://doc.rust-lang.org/std/option/enum.Option.html#trait-.... There are a few things marked “This is a nightly-only experimental API.”, which you can implement yourself if you’re willing to take that stability risk; they’re all linked to try_trait_v2, which is what backs the try operator, `?`. Once it, or its successor, is stabilised, we’ll effectively be back to there being absolutely nothing special about Option, as you’ll be able to implement those traits for your own Option type as well.