Replace &Option<T> with Option<&T> (#5102)

* replace &Option<T> with Option<&T>

* replace Option<&usize> with Option<usize>

* fix clippy error

datafusion/core/src/physical_plan/metrics/mod.rs

@@ -161,8 +161,8 @@ impl Metric {
     }
 
     /// return a reference to the partition
-    pub fn partition(&self) -> &Option<usize> {
-        &self.partition
+    pub fn partition(&self) -> Option<usize> {
+        self.partition
     }
 }
 

datafusion/physical-expr/src/aggregate/stats.rs

@@ -15,7 +15,7 @@
 // specific language governing permissions and limitations
 // under the License.
 
-/// Enum used for differenciating population and sample for statistical functions
+/// Enum used for differentiating population and sample for statistical functions
 #[derive(Debug, Clone, Copy)]
 pub enum StatsType {
     /// Population

datafusion/physical-expr/src/expressions/case.rs

@@ -97,8 +97,8 @@ impl CaseExpr {
     }
 
     /// Optional base expression that can be compared to literal values in the "when" expressions
-    pub fn expr(&self) -> &Option<Arc<dyn PhysicalExpr>> {
-        &self.expr
+    pub fn expr(&self) -> Option<&Arc<dyn PhysicalExpr>> {
+        self.expr.as_ref()
     }
 
     /// One or more when/then expressions

datafusion/physical-expr/src/window/lead_lag.rs

@@ -224,7 +224,7 @@ impl PartitionEvaluator for WindowShiftEvaluator {
         let dtype = array.data_type();
         let idx = self.state.idx as i64 - self.shift_offset;
         if idx < 0 || idx as usize >= array.len() {
-            get_default_value(&self.default_value, dtype)
+            get_default_value(self.default_value.as_ref(), dtype)
         } else {
             ScalarValue::try_from_array(array, idx as usize)
         }
@@ -238,7 +238,7 @@ impl PartitionEvaluator for WindowShiftEvaluator {
 }
 
 fn get_default_value(
-    default_value: &Option<ScalarValue>,
+    default_value: Option<&ScalarValue>,
     dtype: &DataType,
 ) -> Result<ScalarValue> {
     if let Some(value) = default_value {

datafusion/proto/src/physical_plan/to_proto.rs

@@ -187,7 +187,6 @@ impl TryFrom<Arc<dyn PhysicalExpr>> for protobuf::PhysicalExprNode {
                             protobuf::PhysicalCaseNode {
                                 expr: expr
                                     .expr()
-                                    .as_ref()
                                     .map(|exp| exp.clone().try_into().map(Box::new))
                                     .transpose()?,
                                 when_then_expr: expr