1 files changed, 96 insertions, 0 deletions

diff --git a/crates/ra_analysis/src/arena.rs b/crates/ra_analysis/src/arena.rs
new file mode 100644
index 000000000..98ed89274
--- /dev/null
+++ b/crates/ra_analysis/src/arena.rs
@@ -0,0 +1,96 @@
+//! A simple id-based arena, similar to https://github.com/fitzgen/id-arena.
+//! We use our own version for more compact id's and to allow inherent impls
+//! on Ids.
+
+use std::{
+    fmt,
+    ops::{Index, IndexMut},
+    hash::{Hash, Hasher},
+    marker::PhantomData,
+};
+
+pub(crate) struct Id<T> {
+    idx: u32,
+    _ty: PhantomData<fn() -> T>,
+}
+
+impl<T> fmt::Debug for Id<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("Id").field(&self.idx).finish()
+    }
+}
+impl<T> Copy for Id<T> {}
+impl<T> Clone for Id<T> {
+    fn clone(&self) -> Id<T> {
+        *self
+    }
+}
+
+impl<T> PartialEq for Id<T> {
+    fn eq(&self, other: &Id<T>) -> bool {
+        self.idx == other.idx
+    }
+}
+
+impl<T> Eq for Id<T> {}
+
+impl<T> Hash for Id<T> {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        self.idx.hash(h);
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub(crate) struct Arena<T> {
+    data: Vec<T>,
+}
+
+impl<T> Default for Arena<T> {
+    fn default() -> Arena<T> {
+        Arena { data: Vec::new() }
+    }
+}
+
+impl<T> Arena<T> {
+    pub(crate) fn push(&mut self, value: T) -> Id<T> {
+        let id = self.data.len() as u32;
+        self.data.push(value);
+        Id {
+            idx: id as u32,
+            _ty: PhantomData,
+        }
+    }
+
+    pub(crate) fn keys<'a>(&'a self) -> impl Iterator<Item = Id<T>> + 'a {
+        (0..(self.data.len() as u32)).into_iter().map(|idx| Id {
+            idx,
+            _ty: PhantomData,
+        })
+    }
+
+    pub(crate) fn items<'a>(&'a self) -> impl Iterator<Item = (Id<T>, &T)> + 'a {
+        self.data.iter().enumerate().map(|(idx, item)| {
+            let idx = idx as u32;
+            (
+                Id {
+                    idx,
+                    _ty: PhantomData,
+                },
+                item,
+            )
+        })
+    }
+}
+
+impl<T> Index<Id<T>> for Arena<T> {
+    type Output = T;
+    fn index(&self, id: Id<T>) -> &T {
+        &self.data[id.idx as usize]
+    }
+}
+
+impl<T> IndexMut<Id<T>> for Arena<T> {
+    fn index_mut(&mut self, id: Id<T>) -> &mut T {
+        &mut self.data[id.idx as usize]
+    }
+}