defer head_ids creation

Author: mtshiba

src/cycle.rs

@@ -471,16 +471,23 @@ impl Iterator for CycleHeadIdsIterator<'_> {
 /// The context that the cycle recovery function receives when a query cycle occurs.
 #[derive(Clone)]
 pub struct Cycle<'a> {
-    /// An iterator that outputs the [`Id`]s of the current cycle heads.
-    /// This will always contain the [`Id`] of the query being processed by the current cycle recovery function,
-    /// but its position will depend on the query execution order.
-    pub head_ids: CycleHeadIdsIterator<'a>,
+    /// The cycle heads.
+    pub(crate) heads: &'a CycleHeads,
     /// The [`Id`] of the query that the current cycle recovery function is processing.
     pub id: Id,
     /// The counter of the current fixed point iteration.
     pub iteration: u32,
 }
 
+impl Cycle<'_> {
+    /// An iterator that outputs the [`Id`]s of the current cycle heads.
+    /// This will always contain the [`Id`] of the query being processed by the current cycle recovery function,
+    /// but its position will depend on the query execution order.
+    pub fn head_ids(&self) -> CycleHeadIdsIterator<'_> {
+        self.heads.ids()
+    }
+}
+
 #[derive(Debug)]
 pub enum ProvisionalStatus<'db> {
     Provisional {

src/function/execute.rs

@@ -371,7 +371,7 @@ where
             };
 
             let cycle = Cycle {
-                head_ids: cycle_heads.ids(),
+                heads: &cycle_heads,
                 id,
                 iteration: iteration_count.as_u32(),
             };