[tialaramex]

This means C++ is riddled with types that have unrelated "I'm empty" state inside them rather than this being relegated to a separate wrapper type. It's Tony's Billion Dollar Mistake but smeared across an entire ecosystem.

The smart pointer std::unique_ptr<T> is an example of this, sometimes people will say it's basically a boxed T, so analogous to Rust's Box<T> but it isn't quite, it's actually equivalent to Option<Box<T>>. And if we don't want to allow None? Too bad, you can't express that in C++

But you're right that C++ people soldier on, there aren't many C++ types where this nonsense unavoidably gets in your face. std::variant's magic valueless_by_exception is such an example and it's not at all uncommon for C++ people to just pretend it can't happen rather than take it square on.

[spacechild1]

> This means C++ is riddled with types that have unrelated "I'm empty" state

Again, these cases are still rare. Most classes either don't require user-defined move operations, or they have some notion of emptiness or default state.

> And if we don't want to allow None? Too bad, you can't express that in C++

That's actually a good example! Nitpick: you can express it in C++, just not without additional logic and some overhead :)

[7jjjjjjj]

>you can express it in C++, just not without additional logic and some overhead :)

How?

[spacechild1]

E.g. with a boolean member or by setting a bit in the pointer value.

[steveklabnik]

(And that difference leads to an ABI difference that makes it not a zero overhead abstraction in the way that Box is…)

[spacechild1]

Great point! Chandler Carruth explained this in one of this cppcon talks: https://youtu.be/rHIkrotSwcc?t=1047