cloud-fan commented on code in PR #36121:
URL: https://github.com/apache/spark/pull/36121#discussion_r847529275
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sql/catalyst/src/main/scala-2.12/org/apache/spark/sql/catalyst/expressions/ExpressionSet.scala:
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@@ -55,13 +55,22 @@ object ExpressionSet {
* For non-deterministic expressions, they are always considered as not
contained in the [[Set]].
* On adding a non-deterministic expression, simply append it to the original
expressions.
* This is consistent with how we define `semanticEquals` between two
expressions.
+ *
+ * The constructor of this class is protected so caller can only initialize an
Expression from
+ * empty, then build it using `add` and `remove` methods. So every instance of
this class holds the
+ * invariant that:
+ * 1. Every expr `e` in `baseSet` satisfies `e.deterministic &&
e.canonicalized == e`
+ * 2. Every deterministic expr `e` in `originals` satisfies that
`e.canonicalized` is already
+ * accessed.
*/
class ExpressionSet protected(
- private val baseSet: mutable.Set[Expression] = new mutable.HashSet,
- private val originals: mutable.Buffer[Expression] = new ArrayBuffer)
- extends Iterable[Expression] {
+ private val baseSet: mutable.Set[Expression] = new mutable.HashSet,
Review Comment:
nit: 4 spaces indentation here.
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