From<bool> and Bounded's invariant for signed N = 1

Any thoughts?

Hi,

There seems to be an invariant violation in the generic From<bool> implementation for Bounded.

As I understand it, Bounded<i8, 1> can represent only -1 and 0, while i8::from(true) produces 1. However, this safe code is accepted:

let value: Bounded<i8, 1> = true.into();
let _raw: i8 = *value;

Bounded::<i8, 1>::try_new(1) rejects the same value, but From<bool> passes it directly to the unsafe __new() constructor. The resulting Bounded value violates the invariant relied upon by Deref, whose failure branch calls unreachable_unchecked().

Am I missing an intended constraint on this conversion? If not, it seems the signed N = 1 case needs to be excluded or handled differently.

Any thoughts?

Quoted 17 lines

Hi,

There seems to be an invariant violation in the generic From<bool> implementation for Bounded.

As I understand it, Bounded<i8, 1> can represent only -1 and 0, while i8::from(true) produces 1. However, this safe code is accepted:

let value: Bounded<i8, 1> = true.into();
let _raw: i8 = *value;

Bounded::<i8, 1>::try_new(1) rejects the same value, but From<bool> passes it directly to the unsafe __new() constructor. The resulting Bounded value violates the invariant relied upon by Deref, whose failure branch calls unreachable_unchecked().

Quoted 6 lines

Am I missing an intended constraint on this conversion? If not, it seems the signed N = 1 case needs to be excluded or handled differently.

Any thoughts?

I think you are correct. There is a Signedness associated type on the Integer trait, so it should be trivial to exclude signed integers - do you want to send a patch for that?

Thank you both for the feedback. Yes, I can send a patch.

Just to confirm the intended scope: excluding signed integers entirely would also remove valid conversions such as Bounded::<i8, 2>::from(true), since signed Bounded values with N >= 2 can represent both 0 and 1.

Would you prefer the simpler unsigned-only restriction, or should the patch preserve signed conversions for N >= 2?