self-referential iterator

aper/Cargo.toml

@@ -16,3 +16,4 @@ serde = { version = "1.0.204", features = ["derive"] }
 aper_derive = {path = "./aper-derive", version="0.5.0"}
 chrono = { version = "0.4.38", features = ["serde"] }
 tracing = "0.1.40"
+self_cell = "1.0.4"

aper/src/store/iter.rs

@@ -0,0 +1,40 @@
+use super::{core::StoreLayer, PrefixMap, PrefixMapValue};
+use crate::Bytes;
+use self_cell::self_cell;
+use std::{marker::PhantomData, sync::MutexGuard};
+
+struct StoreIteratorInner<'a> {
+    iters: Vec<std::collections::btree_map::Iter<'a, Bytes, PrefixMapValue>>,
+}
+
+self_cell! {
+    struct StoreIterator<'a> {
+        owner: MutexGuard<'a, Vec<StoreLayer>>,
+
+        #[covariant]
+        dependent: StoreIteratorInner,
+    }
+}
+
+impl<'a> StoreIterator<'a> {
+    fn from_guard(prefix: Vec<Bytes>, guard: MutexGuard<'a, Vec<StoreLayer>>) -> Self {
+        StoreIterator::new(guard, |guard| {
+            let mut iters = Vec::new();
+
+            for layer in guard.iter() {
+                match layer.layer.get(&prefix) {
+                    None => continue,
+                    Some(PrefixMap::DeletedPrefixMap) => {
+                        iters.clear();
+                        continue;
+                    }
+                    Some(PrefixMap::Children(map)) => {
+                        iters.push(map.iter());
+                    }
+                }
+            }
+
+            StoreIteratorInner { iters }
+        })
+    }
+}

aper/src/store/mod.rs

@@ -1,5 +1,6 @@
 mod core;
 mod handle;
+mod iter;
 mod prefix_map;
 
 pub use core::Store;