erratic-pattern commented on code in PR #10473:
URL: https://github.com/apache/datafusion/pull/10473#discussion_r1604290031
##########
datafusion/optimizer/src/common_subexpr_eliminate.rs:
##########
@@ -48,7 +51,42 @@ use indexmap::IndexMap;
/// Since an identifier is likely to be copied many times, it is better that
an identifier
/// is small or "copy". otherwise some kinds of reference count is needed.
String
/// description here is not such a good choose.
-type Identifier = String;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+struct Identifier<'n> {
+ hash: u64,
+ expr: &'n Expr,
+}
+
+const SEED: RandomState = RandomState::with_seeds(0, 0, 0, 0);
+
+impl<'n> Identifier<'n> {
+ pub fn new(expr: &'n Expr) -> Self {
+ let mut hasher = SEED.build_hasher();
+ expr.hash_node(&mut hasher);
+ let hash = hasher.finish();
+ Self { hash, expr }
+ }
+
+ pub fn combine(mut self, other: Option<Self>) -> Self {
+ other.map_or(self, |other_id| {
+ self.hash = combine_hashes(self.hash, other_id.hash);
+ self
+ })
+ }
+}
+
+impl Hash for Identifier<'_> {
+ fn hash<H: Hasher>(&self, state: &mut H) {
+ state.write_u64(self.hash);
+ }
+}
+
+impl From<Identifier<'_>> for String {
+ fn from(id: Identifier<'_>) -> Self {
+ format!("common_{}", id.hash)
Review Comment:
maybe "cse" prefix is more specific than "common"?
```suggestion
format!("cse_{}", id.hash)
```
I also think this would be better as a method like `.into_column_name()`
rather than a `From` impl to indicate its purpose and to prevent it from being
accidentally misused.
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