differential_dataflow/trace/cursor/mod.rs
1//! Traits and types for navigating order sequences of update tuples.
2//!
3//! The `Cursor` trait contains several methods for efficiently navigating ordered collections
4//! of tuples of the form `(key, val, time, diff)`. The cursor is different from an iterator
5//! both because it allows navigation on multiple levels (key and val), but also because it
6//! supports efficient seeking (via the `seek_key` and `seek_val` methods).
7
8pub mod cursor_list;
9
10pub use self::cursor_list::CursorList;
11
12use crate::trace::implementations::LayoutExt;
13
14/// A cursor for navigating ordered `(key, val, time, diff)` updates.
15pub trait Cursor : LayoutExt {
16
17 /// Storage required by the cursor.
18 type Storage;
19
20 /// Indicates if the current key is valid.
21 ///
22 /// A value of `false` indicates that the cursor has exhausted all keys.
23 fn key_valid(&self, storage: &Self::Storage) -> bool;
24 /// Indicates if the current value is valid.
25 ///
26 /// A value of `false` indicates that the cursor has exhausted all values for this key.
27 fn val_valid(&self, storage: &Self::Storage) -> bool;
28
29 /// A reference to the current key. Asserts if invalid.
30 fn key<'a>(&self, storage: &'a Self::Storage) -> Self::Key<'a>;
31 /// A reference to the current value. Asserts if invalid.
32 fn val<'a>(&self, storage: &'a Self::Storage) -> Self::Val<'a>;
33
34 /// Returns a reference to the current key, if valid.
35 fn get_key<'a>(&self, storage: &'a Self::Storage) -> Option<Self::Key<'a>>;
36 /// Returns a reference to the current value, if valid.
37 fn get_val<'a>(&self, storage: &'a Self::Storage) -> Option<Self::Val<'a>>;
38
39 /// Applies `logic` to each pair of time and difference. Intended for mutation of the
40 /// closure's scope.
41 fn map_times<L: FnMut(Self::TimeGat<'_>, Self::DiffGat<'_>)>(&mut self, storage: &Self::Storage, logic: L);
42
43 /// Advances the cursor to the next key.
44 fn step_key(&mut self, storage: &Self::Storage);
45 /// Advances the cursor to the specified key.
46 fn seek_key(&mut self, storage: &Self::Storage, key: Self::Key<'_>);
47
48 /// Advances the cursor to the next value.
49 fn step_val(&mut self, storage: &Self::Storage);
50 /// Advances the cursor to the specified value.
51 fn seek_val(&mut self, storage: &Self::Storage, val: Self::Val<'_>);
52
53 /// Rewinds the cursor to the first key.
54 fn rewind_keys(&mut self, storage: &Self::Storage);
55 /// Rewinds the cursor to the first value for current key.
56 fn rewind_vals(&mut self, storage: &Self::Storage);
57
58 /// Rewinds the cursor and outputs its contents to a Vec
59 fn to_vec<K, IK, V, IV>(&mut self, storage: &Self::Storage, into_key: IK, into_val: IV) -> Vec<((K, V), Vec<(Self::Time, Self::Diff)>)>
60 where
61 IK: for<'a> Fn(Self::Key<'a>) -> K,
62 IV: for<'a> Fn(Self::Val<'a>) -> V,
63 {
64 let mut out = Vec::new();
65 self.rewind_keys(storage);
66 while let Some(key) = self.get_key(storage) {
67 self.rewind_vals(storage);
68 while let Some(val) = self.get_val(storage) {
69 let mut kv_out = Vec::new();
70 self.map_times(storage, |ts, r| {
71 kv_out.push((Self::owned_time(ts), Self::owned_diff(r)));
72 });
73 out.push(((into_key(key), into_val(val)), kv_out));
74 self.step_val(storage);
75 }
76 self.step_key(storage);
77 }
78 out
79 }
80}