lexe_std/
iter.rs

1#![allow(clippy::wrong_self_convention)]
2
3use std::cmp;
4
5/// [`Iterator`] extension trait
6pub trait IteratorExt: Iterator {
7    /// Returns `true` iff the iterator is a strict total order. This implies
8    /// the iterator is sorted and all elements are unique.
9    ///
10    /// ```ignore
11    /// [x_1, ..., x_n].is_strict_total_order()
12    ///     := x_1 < x_2 < ... < x_n
13    /// ```
14    ///
15    /// ### Examples
16    ///
17    /// ```rust
18    /// use std::iter;
19    /// use lexe_std::iter::IteratorExt;
20    ///
21    /// assert!(iter::empty::<u32>().is_strict_total_order());
22    /// assert!(&[1].iter().is_strict_total_order());
23    /// assert!(&[1, 2, 6].iter().is_strict_total_order());
24    ///
25    /// assert!(!&[2, 1].iter().is_strict_total_order());
26    /// assert!(!&[1, 2, 2, 3].iter().is_strict_total_order());
27    /// ```
28    fn is_strict_total_order(mut self) -> bool
29    where
30        Self: Sized,
31        Self::Item: PartialOrd,
32    {
33        let mut prev = match self.next() {
34            Some(first) => first,
35            // Trivially true
36            None => return true,
37        };
38
39        for next in self {
40            if let Some(cmp::Ordering::Greater)
41            | Some(cmp::Ordering::Equal)
42            | None = prev.partial_cmp(&next)
43            {
44                return false;
45            }
46            prev = next;
47        }
48
49        true
50    }
51
52    /// Returns `true` iff the iterator is a strict total order according to the
53    /// key extraction function `f`.
54    ///
55    /// ```ignore
56    /// [x_1, ..., x_n].is_strict_total_order_by_key(f)
57    ///     := f(x_1) < f(x_2) < ... < f(x_n)
58    /// ```
59    fn is_strict_total_order_by_key<F, K>(self, f: F) -> bool
60    where
61        Self: Sized,
62        F: FnMut(Self::Item) -> K,
63        K: PartialOrd,
64    {
65        self.map(f).is_strict_total_order()
66    }
67
68    /// Return the minimum and maximum elements of an [`Iterator`], in one pass.
69    #[inline]
70    fn min_max(mut self) -> Option<(Self::Item, Self::Item)>
71    where
72        Self: Sized,
73        Self::Item: Copy + Ord,
74    {
75        let first = self.next()?;
76        let init = (first, first);
77        Some(self.fold(init, |acc, elt| (acc.0.min(elt), acc.1.max(elt))))
78    }
79}
80impl<I: Iterator> IteratorExt for I {}
81
82#[cfg(test)]
83mod test {
84    use proptest::{prop_assert_eq, proptest};
85
86    use super::*;
87
88    #[test]
89    fn test_iter_min_max() {
90        proptest!(|(xs: Vec<u8>)| {
91            let actual = xs.iter().copied().min_max();
92            let expected_min = xs.iter().copied().min();
93            let expected_max = xs.iter().copied().max();
94            let expected = expected_min.zip(expected_max);
95            prop_assert_eq!(actual, expected);
96        });
97    }
98}
lexe_std/iter.rs

lexe_std/
iter.rs
