1 files changed, 48 insertions, 0 deletions

diff --git a/crates/ra_vfs/src/arena.rs b/crates/ra_vfs/src/arena.rs
new file mode 100644
index 000000000..d6fad753b
--- /dev/null
+++ b/crates/ra_vfs/src/arena.rs
@@ -0,0 +1,48 @@
+use std::{
+    hash::{Hash, Hasher},
+    marker::PhantomData,
+    ops::{Index, IndexMut},
+};
+
+#[derive(Clone, Debug)]
+pub(crate) struct Arena<ID: ArenaId, T> {
+    data: Vec<T>,
+    _ty: PhantomData<ID>,
+}
+
+pub(crate) trait ArenaId {
+    fn from_u32(id: u32) -> Self;
+    fn to_u32(self) -> u32;
+}
+
+impl<ID: ArenaId, T> Arena<ID, T> {
+    pub fn alloc(&mut self, value: T) -> ID {
+        let id = self.data.len() as u32;
+        self.data.push(value);
+        ID::from_u32(id)
+    }
+}
+
+impl<ID: ArenaId, T> Default for Arena<ID, T> {
+    fn default() -> Arena<ID, T> {
+        Arena {
+            data: Vec::new(),
+            _ty: PhantomData,
+        }
+    }
+}
+
+impl<ID: ArenaId, T> Index<ID> for Arena<ID, T> {
+    type Output = T;
+    fn index(&self, idx: ID) -> &T {
+        let idx = idx.to_u32() as usize;
+        &self.data[idx]
+    }
+}
+
+impl<ID: ArenaId, T> IndexMut<ID> for Arena<ID, T> {
+    fn index_mut(&mut self, idx: ID) -> &mut T {
+        let idx = idx.to_u32() as usize;
+        &mut self.data[idx]
+    }
+}