1 files changed, 108 insertions, 0 deletions

diff --git a/crates/ra_hir_def/src/dyn_map.rs b/crates/ra_hir_def/src/dyn_map.rs
new file mode 100644
index 000000000..6f269d7b0
--- /dev/null
+++ b/crates/ra_hir_def/src/dyn_map.rs
@@ -0,0 +1,108 @@
+//! This module defines a `DynMap` -- a container for heterogeneous maps.
+//!
+//! This means that `DynMap` stores a bunch of hash maps inside, and those maps
+//! can be of different types.
+//!
+//! It is used like this:
+//!
+//! ```
+//! // keys define submaps of a `DynMap`
+//! const STRING_TO_U32: Key<String, u32> = Key::new();
+//! const U32_TO_VEC: Key<u32, Vec<bool>> = Key::new();
+//!
+//! // Note: concrete type, no type params!
+//! let mut map = DynMap::new();
+//!
+//! // To access a specific map, index the `DynMap` by `Key`:
+//! map[STRING_TO_U32].insert("hello".to_string(), 92);
+//! let value = map[U32_TO_VEC].get(92);
+//! assert!(value.is_none());
+//! ```
+//!
+//! This is a work of fiction. Any similarities to Kotlin's `BindingContext` are
+//! a coincidence.
+use std::{
+    hash::Hash,
+    marker::PhantomData,
+    ops::{Index, IndexMut},
+};
+
+use anymap::Map;
+use rustc_hash::FxHashMap;
+
+pub struct Key<K, V, P = (K, V)> {
+    _phantom: PhantomData<(K, V, P)>,
+}
+
+impl<K, V, P> Key<K, V, P> {
+    pub(crate) const fn new() -> Key<K, V, P> {
+        Key { _phantom: PhantomData }
+    }
+}
+
+impl<K, V, P> Copy for Key<K, V, P> {}
+
+impl<K, V, P> Clone for Key<K, V, P> {
+    fn clone(&self) -> Key<K, V, P> {
+        *self
+    }
+}
+
+pub trait Policy {
+    type K;
+    type V;
+
+    fn insert(map: &mut DynMap, key: Self::K, value: Self::V);
+    fn get<'a>(map: &'a DynMap, key: &Self::K) -> Option<&'a Self::V>;
+}
+
+impl<K: Hash + Eq + 'static, V: 'static> Policy for (K, V) {
+    type K = K;
+    type V = V;
+    fn insert(map: &mut DynMap, key: K, value: V) {
+        map.map.entry::<FxHashMap<K, V>>().or_insert_with(Default::default).insert(key, value);
+    }
+    fn get<'a>(map: &'a DynMap, key: &K) -> Option<&'a V> {
+        map.map.get::<FxHashMap<K, V>>()?.get(key)
+    }
+}
+
+pub struct DynMap {
+    pub(crate) map: Map,
+}
+
+impl Default for DynMap {
+    fn default() -> Self {
+        DynMap { map: Map::new() }
+    }
+}
+
+#[repr(transparent)]
+pub struct KeyMap<KEY> {
+    map: DynMap,
+    _phantom: PhantomData<KEY>,
+}
+
+impl<P: Policy> KeyMap<Key<P::K, P::V, P>> {
+    pub fn insert(&mut self, key: P::K, value: P::V) {
+        P::insert(&mut self.map, key, value)
+    }
+    pub fn get(&self, key: &P::K) -> Option<&P::V> {
+        P::get(&self.map, key)
+    }
+}
+
+impl<P: Policy> Index<Key<P::K, P::V, P>> for DynMap {
+    type Output = KeyMap<Key<P::K, P::V, P>>;
+    fn index(&self, _key: Key<P::K, P::V, P>) -> &Self::Output {
+        // Safe due to `#[repr(transparent)]`.
+        unsafe { std::mem::transmute::<&DynMap, &KeyMap<Key<P::K, P::V, P>>>(self) }
+    }
+}
+
+impl<P: Policy> IndexMut<Key<P::K, P::V, P>> for DynMap {
+    fn index_mut(&mut self, _key: Key<P::K, P::V, P>) -> &mut Self::Output {
+        // Safe due to `#[repr(transparent)]`.
+        unsafe { std::mem::transmute::<&mut DynMap, &mut KeyMap<Key<P::K, P::V, P>>>(self) }
+    }
+}