iter_cartesian

A chainable .cartesian() adapter that yields every (a, b) pair from two iterators, the iterator equivalent of a nested loop.

Usage

use iter_cartesian::CartesianExt;

// collect every (a, b) pair
let pairs: Vec<_> = (0..m).cartesian(0..n).collect();

// iterate in reverse
let rev_pairs: Vec<_> = (0..m).cartesian(0..n).rev().collect();

// O(1) overrides
let item = (0..m).cartesian(0..n).nth(k);
let last = (0..m).cartesian(0..n).last();
let total = (0..m).cartesian(0..n).count();

Features

Chainable .cartesian() method on any double-ended exact-size iterator
Full DoubleEndedIterator support, interleave next() and next_back() correctly
O(1) len, nth, and count via overridden iterator methods
TrustedLen and FusedIterator implementations

Benchmarks

All O(1) operations confirmed flat across input sizes. Collection is ~54% faster than flat_map, with significantly lower variance.

Benchmark	Time
`len`, 10 × 10	455 ps
`len`, 1000 × 1000	449 ps
`len`, 100000 × 100000	447 ps
`nth`, jump 10	16.6 ns
`nth`, jump 100,000	16.9 ns
`nth`, jump 1,000,000	16.6 ns
`collect`, 1000 × 1000	2.48 ms
`flat_map` equivalent	5.44 ms (±1.54 ms)

Alternatives

itertools::iproduct!, macro-based, no DoubleEndedIterator
flat_map, no rev(), no O(1) len, ~54% slower to collect

License