moogle 0.4.4

data structures for relational code
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

use std::cell::Cell;
use std::mem::MaybeUninit;
use std::collections::btree_map;

use crate::id::IdLike;

use super::MoogCell;

pub struct InteriorMapRange<'a, T, K: IdLike, V: 'a> {
    owner: &'a MoogCell<T>,
    state: Cell<u64>, 

    // note: this is safe because Range is not Drop
    value: MaybeUninit<btree_map::Range<'a, K, V>>, 
}

impl<'a, T, K: IdLike, V: 'static> Clone for InteriorMapRange<'a, T, K, V> {
    fn clone(&self) -> Self { 
        InteriorMapRange {
            owner: self.owner,
            state: self.state.clone(),
            value: 
                if self.state.get() == 0 {
                    MaybeUninit::uninit()
                } else {
                    MaybeUninit::new(unsafe {self.value.assume_init_ref()}.clone())
                }
        }
    }
}

impl<T> MoogCell<T> {
    pub fn create_interior_map_range<'a, K: IdLike, V: 'a>(&'a self) -> InteriorMapRange<'a, T, K, V> { 
        InteriorMapRange { 
            owner: self, 
            state: Cell::new(0), 
            value: MaybeUninit::uninit(),
        }
    }
}

impl<'a, T, K: IdLike, V: 'a> InteriorMapRange<'a, T, K, V> {
    pub(crate) fn get_or_compute<Out>(
        &mut self, 
        compute: impl for<'b> FnOnce(&'b T) -> btree_map::Range<'b, K, V>,
        body: impl for<'e> FnOnce(&mut btree_map::Range<'e, K, V>) -> Out
    ) -> Out {
        // panic if someone else borrowed our owner
        // (which would imply there is a &mut to it somewhere)
        let borrow = self.owner.borrow();

        // ok let's go!
        let og = self.owner.state.get();
        if self.state.get() != og {
            self.state.replace(og);

            let value: btree_map::Range<'_, K, V> = compute(&borrow);
            let longer_value: btree_map::Range<'a, K, V> = unsafe { std::mem::transmute(value) };
            self.value = MaybeUninit::new(longer_value);
        }

        let result = body(unsafe { self.value.assume_init_mut() });
        std::mem::drop(borrow);
        result
    }
}