indexmap 1.1.0

A hash table with consistent order and fast iteration. The indexmap is a hash table where the iteration order of the key-value pairs is independent of the hash values of the keys. It has the usual hash table functionality, it preserves insertion order except after removals, and it allows lookup of its elements by either hash table key or numerical index. A corresponding hash set type is also provided. This crate was initially published under the name ordermap, but it was renamed to indexmap.
Documentation 
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use std::iter::Enumerate;
use std::mem::size_of;

pub fn third<A, B, C>(t: (A, B, C)) -> C { t.2 }

pub fn enumerate<I>(iterable: I) -> Enumerate<I::IntoIter>
    where I: IntoIterator
{
    iterable.into_iter().enumerate()
}

/// return the number of steps from a to b
pub fn ptrdistance<T>(a: *const T, b: *const T) -> usize {
    debug_assert!(a as usize <= b as usize);
    (b as usize - a as usize) / size_of::<T>()
}