Update the doc comments for drain to make it clear that the origina…

…l value is left empty.

crates/bevy_reflect/src/list.rs

@@ -94,7 +94,9 @@ pub trait List: PartialReflect {
     /// Returns an iterator over the list.
     fn iter(&self) -> ListIter;
 
-    /// Drain the elements of this list to get a vector of owned values.
+    /// Drain the elements of this list to get a vector of owned values. After calling this
+    /// function, `self` will be empty. The order of items in the returned
+    /// [`Vec`] will match the order of items in `self`.
     fn drain(&mut self) -> Vec<Box<dyn PartialReflect>>;
 
     /// Clones the list, producing a [`DynamicList`].

crates/bevy_reflect/src/map.rs

@@ -71,7 +71,8 @@ pub trait Map: PartialReflect {
     /// Returns an iterator over the key-value pairs of the map.
     fn iter(&self) -> MapIter;
 
-    /// Drain the key-value pairs of this map to get a vector of owned values.
+    /// Drain the key-value pairs of this map to get a vector of owned values. After calling this
+    /// function, `self` will be empty.
     fn drain(&mut self) -> Vec<(Box<dyn PartialReflect>, Box<dyn PartialReflect>)>;
 
     /// Clones the map, producing a [`DynamicMap`].

crates/bevy_reflect/src/set.rs

@@ -57,7 +57,8 @@ pub trait Set: PartialReflect {
     /// Returns an iterator over the values of the set.
     fn iter(&self) -> Box<dyn Iterator<Item = &dyn PartialReflect> + '_>;
 
-    /// Drain the values of this set to get a vector of owned values.
+    /// Drain the values of this set to get a vector of owned values. After calling this function,
+    /// `self` will be empty.
     fn drain(&mut self) -> Vec<Box<dyn PartialReflect>>;
 
     /// Clones the set, producing a [`DynamicSet`].