From 92318c808666695fb5c2f358083f1cb13158dca9 Mon Sep 17 00:00:00 2001
From: Peter Toth <peter.toth@gmail.com>
Date: Thu, 18 Apr 2024 15:27:32 +0200
Subject: [PATCH] Add default for `Expr` (#10127)

---
 datafusion/expr/src/expr.rs                           | 6 ++++++
 datafusion/optimizer/src/unwrap_cast_in_comparison.rs | 8 +++-----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/datafusion/expr/src/expr.rs b/datafusion/expr/src/expr.rs
index cffb58dadd8e..2a8fe4ca90a5 100644
--- a/datafusion/expr/src/expr.rs
+++ b/datafusion/expr/src/expr.rs
@@ -184,6 +184,12 @@ pub enum Expr {
     Unnest(Unnest),
 }
 
+impl Default for Expr {
+    fn default() -> Self {
+        Expr::Literal(ScalarValue::Null)
+    }
+}
+
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub struct Unnest {
     pub expr: Box<Expr>,
diff --git a/datafusion/optimizer/src/unwrap_cast_in_comparison.rs b/datafusion/optimizer/src/unwrap_cast_in_comparison.rs
index bd14584fd5c1..1d80e235e7e9 100644
--- a/datafusion/optimizer/src/unwrap_cast_in_comparison.rs
+++ b/datafusion/optimizer/src/unwrap_cast_in_comparison.rs
@@ -179,8 +179,7 @@ impl TreeNodeRewriter for UnwrapCastExprRewriter {
                         };
                         **left = lit(value);
                         // unwrap the cast/try_cast for the right expr
-                        **right =
-                            mem::replace(right_expr, Expr::Literal(ScalarValue::Null));
+                        **right = mem::take(right_expr);
                         Ok(Transformed::yes(expr))
                     }
                     (
@@ -203,8 +202,7 @@ impl TreeNodeRewriter for UnwrapCastExprRewriter {
                             return Ok(Transformed::no(expr));
                         };
                         // unwrap the cast/try_cast for the left expr
-                        **left =
-                            mem::replace(left_expr, Expr::Literal(ScalarValue::Null));
+                        **left = mem::take(left_expr);
                         **right = lit(value);
                         Ok(Transformed::yes(expr))
                     }
@@ -262,7 +260,7 @@ impl TreeNodeRewriter for UnwrapCastExprRewriter {
                     .collect::<Result<Vec<_>>>() else {
                     return Ok(Transformed::no(expr))
                 };
-                **left = mem::replace(left_expr, Expr::Literal(ScalarValue::Null));
+                **left = mem::take(left_expr);
                 *list = right_exprs;
                 Ok(Transformed::yes(expr))
             }