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: &usize, i: &PutBack, j: &PutBack) => f&mut DebugTuple<'_, '_>
41 .debug_tuple(name:"FirstMismatch")
42 .field(idx)
43 .field(i)
44 .field(j)
45 .finish(),
46 Self::Shorter(idx: &usize, i: &PutBack) => f.debug_tuple(name:"Shorter").field(idx).field(i).finish(),
47 Self::Longer(idx: &usize, j: &PutBack) => f.debug_tuple(name:"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: &usize, i: &PutBack, j: &PutBack) => Self::FirstMismatch(*idx, i.clone(), j.clone()),
62 Self::Shorter(idx: &usize, i: &PutBack) => Self::Shorter(*idx, i.clone()),
63 Self::Longer(idx: &usize, j: &PutBack) => 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, is_equal: F) -> Option<Diff<I::IntoIter, J::IntoIter>>
81where
82 I: IntoIterator,
83 J: IntoIterator,
84 F: Fn(&I::Item, &J::Item) -> bool,
85{
86 let mut i: I = i.into_iter();
87 let mut j: J = j.into_iter();
88 let mut idx: usize = 0;
89 while let Some(i_elem) = i.next() {
90 match j.next() {
91 None => return Some(Diff::Shorter(idx, put_back(iterable:i).with_value(i_elem))),
92 Some(j_elem) => {
93 if !is_equal(&i_elem, &j_elem) {
94 let remaining_i: PutBack = put_back(iterable:i).with_value(i_elem);
95 let remaining_j: PutBack = put_back(iterable:j).with_value(j_elem);
96 return Some(Diff::FirstMismatch(idx, remaining_i, remaining_j));
97 }
98 }
99 }
100 idx += 1;
101 }
102 jOption<{unknown}>.next()
103 .map(|j_elem| Diff::Longer(idx, put_back(iterable:j).with_value(j_elem)))
104}
105