computer: convert stores to vecs part 1

crates/brk_computer/src/stateful/range_map.rs

@@ -0,0 +1,35 @@
+use std::collections::BTreeMap;
+
+use brk_vec::{IndexedVec, StoredIndex, StoredType};
+
+#[derive(Debug)]
+pub struct RangeMap<I, T>(BTreeMap<I, T>);
+
+impl<I, T> RangeMap<I, T>
+where
+    I: StoredIndex,
+    T: StoredIndex,
+{
+    pub fn get(&self, key: I) -> Option<&T> {
+        self.0.range(..=key).next_back().map(|(&min, value)| {
+            if min > key {
+                unreachable!()
+            }
+            value
+        })
+    }
+}
+
+impl<I, T> From<&IndexedVec<I, T>> for RangeMap<T, I>
+where
+    I: StoredIndex,
+    T: StoredIndex + StoredType,
+{
+    fn from(vec: &IndexedVec<I, T>) -> Self {
+        Self(
+            vec.into_iter()
+                .map(|(i, v)| (v.into_owned(), i))
+                .collect::<BTreeMap<_, _>>(),
+        )
+    }
+}