itertools/
diff.rs

1//! "Diff"ing iterators for caching elements to sequential collections without requiring the new
2//! elements' iterator to be `Clone`.
3//!
4//! [`Diff`] (produced by the [`diff_with`] function)
5//! describes the difference between two non-`Clone` iterators `I` and `J` after breaking ASAP from
6//! a lock-step comparison.
7
8use std::fmt;
9
10use crate::free::put_back;
11use crate::structs::PutBack;
12
13/// A type returned by the [`diff_with`] function.
14///
15/// `Diff` represents the way in which the elements yielded by the iterator `I` differ to some
16/// iterator `J`.
17pub enum Diff<I, J>
18where
19    I: Iterator,
20    J: Iterator,
21{
22    /// The index of the first non-matching element along with both iterator's remaining elements
23    /// starting with the first mis-match.
24    FirstMismatch(usize, PutBack<I>, PutBack<J>),
25    /// The total number of elements that were in `J` along with the remaining elements of `I`.
26    Shorter(usize, PutBack<I>),
27    /// The total number of elements that were in `I` along with the remaining elements of `J`.
28    Longer(usize, PutBack<J>),
29}
30
31impl<I, J> fmt::Debug for Diff<I, J>
32where
33    I: Iterator,
34    J: Iterator,
35    PutBack<I>: fmt::Debug,
36    PutBack<J>: fmt::Debug,
37{
38    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
39        match self {
40            Self::FirstMismatch(idx, i, j) => f
41                .debug_tuple("FirstMismatch")
42                .field(idx)
43                .field(i)
44                .field(j)
45                .finish(),
46            Self::Shorter(idx, i) => f.debug_tuple("Shorter").field(idx).field(i).finish(),
47            Self::Longer(idx, j) => f.debug_tuple("Longer").field(idx).field(j).finish(),
48        }
49    }
50}
51
52impl<I, J> Clone for Diff<I, J>
53where
54    I: Iterator,
55    J: Iterator,
56    PutBack<I>: Clone,
57    PutBack<J>: Clone,
58{
59    fn clone(&self) -> Self {
60        match self {
61            Self::FirstMismatch(idx, i, j) => Self::FirstMismatch(*idx, i.clone(), j.clone()),
62            Self::Shorter(idx, i) => Self::Shorter(*idx, i.clone()),
63            Self::Longer(idx, j) => Self::Longer(*idx, j.clone()),
64        }
65    }
66}
67
68/// Compares every element yielded by both `i` and `j` with the given function in lock-step and
69/// returns a [`Diff`] which describes how `j` differs from `i`.
70///
71/// If the number of elements yielded by `j` is less than the number of elements yielded by `i`,
72/// the number of `j` elements yielded will be returned along with `i`'s remaining elements as
73/// `Diff::Shorter`.
74///
75/// If the two elements of a step differ, the index of those elements along with the remaining
76/// elements of both `i` and `j` are returned as `Diff::FirstMismatch`.
77///
78/// If `i` becomes exhausted before `j` becomes exhausted, the number of elements in `i` along with
79/// the remaining `j` elements will be returned as `Diff::Longer`.
80pub fn diff_with<I, J, F>(i: I, j: J, mut is_equal: F) -> Option<Diff<I::IntoIter, J::IntoIter>>
81where
82    I: IntoIterator,
83    J: IntoIterator,
84    F: FnMut(&I::Item, &J::Item) -> bool,
85{
86    let mut i = i.into_iter();
87    let mut j = j.into_iter();
88    let mut idx = 0;
89    while let Some(i_elem) = i.next() {
90        match j.next() {
91            None => return Some(Diff::Shorter(idx, put_back(i).with_value(i_elem))),
92            Some(j_elem) => {
93                if !is_equal(&i_elem, &j_elem) {
94                    let remaining_i = put_back(i).with_value(i_elem);
95                    let remaining_j = put_back(j).with_value(j_elem);
96                    return Some(Diff::FirstMismatch(idx, remaining_i, remaining_j));
97                }
98            }
99        }
100        idx += 1;
101    }
102    j.next()
103        .map(|j_elem| Diff::Longer(idx, put_back(j).with_value(j_elem)))
104}
itertools/diff.rs

itertools/
diff.rs
