1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
//! A region that stores options.

#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};

use crate::{Containerized, IntoOwned, Push, Region, ReserveItems};

impl<T: Containerized> Containerized for Option<T> {
    type Region = OptionRegion<T::Region>;
}

/// A region to hold [`Option`]s.
///
/// # Examples
///
/// The region can hold options:
/// ```
/// # use flatcontainer::{Containerized, Push, OptionRegion, Region};
/// let mut r = <OptionRegion<<u8 as Containerized>::Region>>::default();
///
/// let some_index = r.push(Some(123));
/// // Type annotations required for `None`:
/// let none_index = r.push(Option::<u8>::None);
///
/// assert_eq!(Some(123), r.index(some_index));
/// assert_eq!(None, r.index(none_index));
/// ```
#[derive(Default, Debug, Clone)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct OptionRegion<R> {
    inner: R,
}

impl<R: Region> Region for OptionRegion<R> {
    type Owned = Option<R::Owned>;
    type ReadItem<'a> = Option<<R as Region>::ReadItem<'a>> where Self: 'a;
    type Index = Option<R::Index>;

    #[inline]
    fn merge_regions<'a>(regions: impl Iterator<Item = &'a Self> + Clone) -> Self
    where
        Self: 'a,
    {
        Self {
            inner: R::merge_regions(regions.map(|r| &r.inner)),
        }
    }

    #[inline]
    fn index(&self, index: Self::Index) -> Self::ReadItem<'_> {
        index.map(|t| self.inner.index(t))
    }

    #[inline]
    fn reserve_regions<'a, I>(&mut self, regions: I)
    where
        Self: 'a,
        I: Iterator<Item = &'a Self> + Clone,
    {
        self.inner.reserve_regions(regions.map(|r| &r.inner));
    }

    #[inline]
    fn clear(&mut self) {
        self.inner.clear();
    }

    #[inline]
    fn heap_size<F: FnMut(usize, usize)>(&self, callback: F) {
        self.inner.heap_size(callback);
    }

    #[inline]
    fn reborrow<'b, 'a: 'b>(item: Self::ReadItem<'a>) -> Self::ReadItem<'b>
    where
        Self: 'a,
    {
        item.map(R::reborrow)
    }
}

impl<'a, T> IntoOwned<'a> for Option<T>
where
    T: IntoOwned<'a>,
{
    type Owned = Option<T::Owned>;

    #[inline]
    fn into_owned(self) -> Self::Owned {
        self.map(IntoOwned::into_owned)
    }

    #[inline]
    fn clone_onto(self, other: &mut Self::Owned) {
        match (self, other) {
            (Some(item), Some(target)) => T::clone_onto(item, target),
            (Some(item), target) => *target = Some(T::into_owned(item)),
            (None, target) => *target = None,
        }
    }

    #[inline]
    fn borrow_as(owned: &'a Self::Owned) -> Self {
        owned.as_ref().map(T::borrow_as)
    }
}

impl<T, TR> Push<Option<T>> for OptionRegion<TR>
where
    TR: Region + Push<T>,
{
    #[inline]
    fn push(&mut self, item: Option<T>) -> <OptionRegion<TR> as Region>::Index {
        item.map(|t| self.inner.push(t))
    }
}

impl<'a, T: 'a, TR> Push<&'a Option<T>> for OptionRegion<TR>
where
    TR: Region + Push<&'a T>,
{
    #[inline]
    fn push(&mut self, item: &'a Option<T>) -> <OptionRegion<TR> as Region>::Index {
        item.as_ref().map(|t| self.inner.push(t))
    }
}

impl<'a, T: 'a, TR> ReserveItems<&'a Option<T>> for OptionRegion<TR>
where
    TR: Region + ReserveItems<&'a T>,
{
    #[inline]
    fn reserve_items<I>(&mut self, items: I)
    where
        I: Iterator<Item = &'a Option<T>> + Clone,
    {
        self.inner.reserve_items(items.filter_map(|r| r.as_ref()));
    }
}

#[cfg(test)]
mod tests {
    use crate::{MirrorRegion, OwnedRegion, Region, ReserveItems};

    use super::*;

    #[test]
    fn test_reserve() {
        let mut r = <OptionRegion<MirrorRegion<u8>>>::default();
        ReserveItems::reserve_items(&mut r, [Some(0), None].iter());
    }

    #[test]
    fn test_heap_size() {
        let mut r = <OptionRegion<OwnedRegion<u8>>>::default();
        ReserveItems::reserve_items(&mut r, [Some([1; 1]), None].iter());
        let mut cap = 0;
        r.heap_size(|_, ca| {
            cap += ca;
        });
        assert!(cap > 0);
    }
}