Function ipnsort 

fn ipnsort<T, F>(v: &mut [T], is_less: &mut F)
where
    F: FnMut(&T, &T) -> bool,

🔬This is a nightly-only experimental API. (slice_internals)

Available on neither crate feature optimize_for_size.

See sort

Deliberately don’t inline the main sorting routine entrypoint to ensure the inlined insertion sort i-cache footprint remains minimal.