reactivity base

src/util/id.rs

@@ -0,0 +1,43 @@
+/// intentionally does not implement copy or clone
+/// which should make it harder to misuse;
+/// the idea is to generally try to guarantee all IDs
+/// point to something valid, although duplicate
+/// gets around this if needed
+#[derive(Eq, Hash, PartialEq, Debug)]
+pub struct ID(usize);
+
+#[derive(Default)]
+pub struct IDTracker {
+    free: Vec<ID>,
+    cur: usize,
+}
+
+impl IDTracker {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    #[allow(clippy::should_implement_trait)]
+    pub fn next(&mut self) -> ID {
+        if let Some(id) = self.free.pop() {
+            return id;
+        }
+        let id = ID(self.cur);
+        self.cur += 1;
+        id
+    }
+
+    pub fn free(&mut self, id: ID) {
+        self.free.push(id);
+    }
+}
+
+impl ID {
+    /// this must be used carefully to make sure
+    /// all IDs are still valid references;
+    /// named weirdly to indicate this.
+    /// generally should not be used in "user" code
+    pub fn duplicate(&self) -> Self {
+        Self(self.0)
+    }
+}