[comex]

I misinterpreted your comment; I thought you meant ranges that were so large they couldn't fit in any integer type (presumably of floats).

But actually, it's weirder than I thought.

RangeInclusive doesn't have an inherent len() method, but one is provided by the ExactSizeIterator trait, which is implemented only when the underlying type is i8, u8, i16, or u16. len() always returns usize, regardless of the original type; thus I believe the reason for that particular list of types is that usize is only guaranteed to be at least 16 bits. But I'm not sure why it's not also implemented for RangeInclusive<usize> and RangeInclusive<isize>...

[eridius]

RangeInclusive is inclusive. This means `0..=0` has a length of 1. Therefore `0..=usize::MAX` has a length of usize::MAX + 1.

[ridiculous_fish]

Nice, thanks for the complete answer. It's a highly principled (and perhaps frustrating) design, in keeping with Rust's ethos.

By way of comparison, Swift overflows and returns a length of 0. Oh well.