sign-bound  

Signed integer types for Rust that are bounded to be either positive or negative. The API is analogous to the built-in NonZero types:

• PositiveI8, NegativeI8
• PositiveI16, NegativeI16
• PositiveI32, NegativeI32
• PositiveI64, NegativeI64
• PositiveIsize, NegativeIsize

The types are all memory-layout optimized, so for example Option<PositiveI32> and Option<NegativeI32> are both the same size as i32. Using additional variants in an enum can also have some space benefits.

enum MyEnum {
    A(PositiveI16),
    B,
    C,
    D,
}
assert_eq!(size_of::<MyEnum>(), size_of::<PositiveI16>());

Note that due to the implementation details of this crate, the space optimization for any type will not occur if there are more than 128 additional enum variants.

Option<PositiveIsize> is particularly useful as a space-efficient optional Vec index, since Rust's Vec structure is limited to isize::MAX entries.