Fix stores with vec index method and expose opaque writer types (#4684)

* Use a different indexing method for each data structure

* add a get method for slices

* Rename trait for clarity and simplicity

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/stores/src/impls/btreemap.rs

@@ -1,3 +1,5 @@
+//! Additional utilities for `BTreeMap` stores.
+
 use std::{borrow::Borrow, collections::BTreeMap, hash::Hash, iter::FusedIterator};
 
 use crate::{store::Store, ReadStore};

packages/stores/src/impls/hashmap.rs

@@ -1,3 +1,5 @@
+//! Additional utilities for `HashMap` stores.
+
 use std::{
     borrow::Borrow,
     collections::HashMap,

packages/stores/src/impls/index.rs

@@ -1,14 +1,54 @@
+//! Additional utilities for indexing into stores.
+
 use std::{
+    collections::{BTreeMap, HashMap},
     hash::Hash,
     ops::{self, Index, IndexMut},
 };
 
-use crate::{store::Store, ReadStore};
+use crate::{scope::SelectorScope, store::Store, ReadStore};
 use dioxus_signals::{
     AnyStorage, BorrowError, BorrowMutError, ReadSignal, Readable, UnsyncStorage, Writable,
     WriteLock, WriteSignal,
 };
 
+/// The way a data structure index into its children based on a key. The selector must use this indexing
+/// method consistently to ensure that the same key always maps to the same child.
+pub trait IndexSelector<Idx> {
+    /// Given a selector and an index, scope the selector to the child at the given index.
+    fn scope_selector<Lens>(selector: SelectorScope<Lens>, index: &Idx) -> SelectorScope<Lens>;
+}
+
+impl<T> IndexSelector<usize> for Vec<T> {
+    fn scope_selector<Lens>(selector: SelectorScope<Lens>, index: &usize) -> SelectorScope<Lens> {
+        selector.child_unmapped(*index as _)
+    }
+}
+
+impl<T> IndexSelector<usize> for [T] {
+    fn scope_selector<Lens>(selector: SelectorScope<Lens>, index: &usize) -> SelectorScope<Lens> {
+        selector.child_unmapped(*index as _)
+    }
+}
+
+impl<K, V, I> IndexSelector<I> for HashMap<K, V>
+where
+    I: Hash,
+{
+    fn scope_selector<Lens>(selector: SelectorScope<Lens>, index: &I) -> SelectorScope<Lens> {
+        selector.hash_child_unmapped(&index)
+    }
+}
+
+impl<K, V, I> IndexSelector<I> for BTreeMap<K, V>
+where
+    I: Hash,
+{
+    fn scope_selector<Lens>(selector: SelectorScope<Lens>, index: &I) -> SelectorScope<Lens> {
+        selector.hash_child_unmapped(&index)
+    }
+}
+
 impl<Lens, T> Store<T, Lens> {
     /// Index into the store, returning a store that allows access to the item at the given index. The
     /// new store will only update when the item at the index changes.
@@ -23,12 +63,10 @@ impl<Lens, T> Store<T, Lens> {
     /// ```
     pub fn index<Idx>(self, index: Idx) -> Store<T::Output, IndexWrite<Idx, Lens>>
     where
-        T: IndexMut<Idx> + 'static,
-        Idx: Hash + 'static,
+        T: IndexMut<Idx> + 'static + IndexSelector<Idx>,
         Lens: Readable<Target = T> + 'static,
     {
-        self.into_selector()
-            .hash_child_unmapped(&index)
+        T::scope_selector(self.into_selector(), &index)
             .map_writer(move |write| IndexWrite { index, write })
             .into()
     }

packages/stores/src/impls/mod.rs

@@ -1,7 +1,7 @@
-mod btreemap;
+pub mod btreemap;
 mod deref;
-mod hashmap;
-mod index;
+pub mod hashmap;
+pub mod index;
 mod option;
 mod result;
 mod slice;

packages/stores/src/impls/slice.rs

@@ -57,4 +57,27 @@ where
     {
         (0..self.len()).map(move |i| self.clone().index(i))
     }
+
+    /// Try to get an item from slice. This will only track the shallow state of the slice.
+    /// It will only cause a re-run if the length of the slice could change. The new store
+    /// will only update when the item at the index changes.
+    ///
+    /// # Example
+    /// ```rust, no_run
+    /// use dioxus_stores::*;
+    /// let store = use_store(|| vec![1, 2, 3]);
+    /// let indexed_store = store.get(1).unwrap();
+    /// // The indexed store can access the store methods of the indexed store.
+    /// assert_eq!(indexed_store(), 2);
+    /// ```
+    pub fn get(&self, index: usize) -> Option<Store<I, IndexWrite<usize, Lens>>>
+    where
+        Lens: Clone,
+    {
+        if index >= self.len() {
+            None
+        } else {
+            Some(self.clone().index(index))
+        }
+    }
 }

packages/stores/src/lib.rs

@@ -7,6 +7,7 @@
 mod impls;
 mod store;
 mod subscriptions;
+pub use impls::*;
 pub use store::*;
 pub mod scope;