diem_proptest_helpers/
growing_subset.rs

1// Copyright (c) The Diem Core Contributors
2// SPDX-License-Identifier: Apache-2.0
3
4// Copyright 2021 Conflux Foundation. All rights reserved.
5// Conflux is free software and distributed under GNU General Public License.
6// See http://www.gnu.org/licenses/
7
8use proptest::sample::Index;
9use std::iter::FromIterator;
10
11/// A set of elements, each with an associated key, that grows over time.
12///
13/// This is called `GrowingSubset` because the universal set the subset grows
14/// from is provided upfront. At any time, the items included form the *current
15/// subset*.
16///
17/// `GrowingSubset` integrates with `proptest` through the
18/// [`pick_item`][GrowingSubset::pick_item] and [`pick_value`][GrowingSubset::
19/// pick_value] methods.
20///
21/// # Examples
22///
23/// ```
24/// use diem_proptest_helpers::GrowingSubset;
25/// let items = vec![(1, "a"), (3, "c"), (2, "b"), (2, "d")];
26/// let mut subset: GrowingSubset<_, _> = items.into_iter().collect();
27///
28/// assert_eq!(subset.total_len(), 4);
29/// assert_eq!(subset.len(), 0);
30/// assert_eq!(subset.current(), &[]);
31///
32/// subset.advance_to(&2);
33/// assert_eq!(subset.len(), 1);
34/// assert_eq!(subset.current(), &[(1, "a")]);
35///
36/// subset.advance_to(&4);
37/// assert_eq!(subset.len(), 4);
38/// assert_eq!(subset.current(), &[(1, "a"), (2, "b"), (2, "d"), (3, "c")]);
39///
40/// subset.advance_to(&5);
41/// assert_eq!(subset.len(), 4);
42/// assert_eq!(subset.current(), &[(1, "a"), (2, "b"), (2, "d"), (3, "c")]);
43/// ```
44#[derive(Clone, Debug)]
45pub struct GrowingSubset<Ix, T> {
46    // `items` needs to be in ascending order by index -- constructors of
47    // `GrowingSubset` should sort the list of items.
48    items: Vec<(Ix, T)>,
49    current_pos: usize,
50}
51
52/// Constructs a `GrowingSubset` from an iterator of (index, value) pairs.
53///
54/// The input does not need to be pre-sorted.
55impl<Ix, T> FromIterator<(Ix, T)> for GrowingSubset<Ix, T>
56where Ix: Ord
57{
58    fn from_iter<I>(iter: I) -> Self
59    where I: IntoIterator<Item = (Ix, T)> {
60        let mut items: Vec<_> = iter.into_iter().collect();
61        // Sorting is required to construct a subset correctly.
62        items.sort_by(|x, y| x.0.cmp(&y.0));
63        Self {
64            items,
65            current_pos: 0,
66        }
67    }
68}
69
70impl<Ix, T> GrowingSubset<Ix, T>
71where Ix: Ord
72{
73    /// Returns the number of elements in the *current subset*.
74    ///
75    /// See [`total_len`](GrowingSubset::total_len) for the length of the
76    /// universal set.
77    pub fn len(&self) -> usize { self.current_pos }
78
79    /// Returns `true` if the *current subset* contains no elements.
80    pub fn is_empty(&self) -> bool { self.len() == 0 }
81
82    /// Returns the total number of elements in the universal set.
83    ///
84    /// This remains fixed once the `GrowingSubset` has been created.
85    pub fn total_len(&self) -> usize { self.items.len() }
86
87    /// Returns a slice containing the items in the *current subset*.
88    pub fn current(&self) -> &[(Ix, T)] { &self.items[0..self.current_pos] }
89
90    /// Chooses an (index, value) pair from the *current subset* using the
91    /// provided [`Index`](proptest::sample::Index) instance as the source
92    /// of randomness.
93    pub fn pick_item(&self, index: &Index) -> &(Ix, T) {
94        index.get(self.current())
95    }
96
97    /// Chooses a value from the *current subset* using the provided
98    /// [`Index`](proptest::sample::Index) instance as the source of randomness.
99    pub fn pick_value(&self, index: &Index) -> &T { &self.pick_item(index).1 }
100
101    /// Advances the valid subset to the provided index. After the end of this,
102    /// the *current subset* will contain all elements where the index is
103    /// *less than* `to_idx`.
104    ///
105    /// If duplicate indexes exist, `advance_to` will cause all of the
106    /// corresponding items to be included.
107    ///
108    /// It is expected that `advance_to` will be called with larger indexes over
109    /// time.
110    pub fn advance_to(&mut self, to_idx: &Ix) {
111        let len = self.items.len();
112        while self.current_pos < len {
113            let (idx, _) = &self.items[self.current_pos];
114            if idx >= to_idx {
115                break;
116            }
117            self.current_pos += 1;
118        }
119    }
120}
diem_proptest_helpers/growing_subset.rs

diem_proptest_helpers/
growing_subset.rs
