peter-toth commented on code in PR #7942:
URL: https://github.com/apache/arrow-datafusion/pull/7942#discussion_r1432393865
##########
datafusion/expr/src/expr.rs:
##########
@@ -81,8 +81,10 @@ use std::sync::Arc;
/// assert_eq!(binary_expr.op, Operator::Eq);
/// }
/// ```
-#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, PartialEq, Eq, Hash, Debug, Default)]
pub enum Expr {
+ #[default]
Review Comment:
The reason why I added `Expr::Nop` is to be able to refactor `unalias()` to
be self mutating one:
https://github.com/apache/arrow-datafusion/pull/7942/files#diff-204cfc4f999c3d12dc065f323cb952fb0ecb33c5570eed8dc1fb52b806e87004R960.
I needed a dummy `Expr` for `mem::take()`, but as you showed in
https://github.com/apache/arrow-datafusion/pull/7942/files#r1431799873
`unalias()` doens't need to be self mutating.
But, maybe having a default dummy value of `Expr` is still useful in some
cases, like in @sadboy's PR:
https://github.com/apache/arrow-datafusion/pull/8591/files#diff-6515fda3c67b9d487ab491fd21c27e32c411a8cbee24725d737290d19c10c199R388-R389,
https://github.com/apache/arrow-datafusion/pull/8591/files#diff-6515fda3c67b9d487ab491fd21c27e32c411a8cbee24725d737290d19c10c199R427-R428,
`Expr::Wildcard { qualifier: None }` is used for such purposes.
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