fluent-iterable 1.0.1

Fluent extension trait for std Iterator, port of @codibre/fluent-iterable vocabulary: joins, grouping, distinctness, cardinality checks
Documentation 
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// Tests for the distinct family (spliced into `lib.rs`'s test module).

    #[test]
    fn distinct_by_is_lazy_and_short_circuits() {
        // take(k) must stop pulling the source at the k-th distinct key —
        // impossible for an eager implementation (the design bug this
        // replaced).
        let (source, counter) = counting([1, 1, 2, 2, 3, 3, 4, 4].into_iter());
        let out: Vec<i32> = source.distinct_by(|x| *x).take(2).collect();
        assert_eq!(out, vec![1, 2]);
        assert_eq!(counter.get(), 3); // pulled up to the second `2`, no further
    }


    #[test]
    fn distinct_is_lazy_and_short_circuits() {
        let (source, counter) = counting([1, 1, 2, 3, 3, 3, 4].into_iter());
        let out: Vec<i32> = source.distinct().take(2).collect();
        assert_eq!(out, vec![1, 2]);
        // stopped right after discovering 2 (never walked the tail)
        assert!(counter.get() <= 4, "consumed {}", counter.get());
    }


    #[test]
    fn distinct_keeps_first_per_key() {
        let items = ["bb", "a1", "b1", "a2", "c"];
        let out: Vec<_> = items
            .into_iter()
            .distinct_by(|s| s.chars().next().unwrap())
            .collect();
        assert_eq!(out, vec!["bb", "a1", "c"]);
    }


    #[test]
    fn is_distinct_by_short_circuits() {
        assert!([("a", 1), ("b", 2)].into_iter().is_distinct_by(|(k, _)| *k));
        let (source, counter) = counting([("a", 1), ("b", 2), ("a", 3), ("b", 4)].into_iter());
        assert!(!source.is_distinct_by(|(k, _)| *k));
        assert_eq!(counter.get(), 3);
    }


    #[test]
    fn is_distinct_checks_and_short_circuits() {
        assert!([1, 2, 3].into_iter().is_distinct());
        assert!(std::iter::empty::<i32>().is_distinct());
        let (source, counter) = counting([1, 2, 1, 2, 1].into_iter());
        assert!(!source.is_distinct());
        assert_eq!(counter.get(), 3);
    }