ENH: treat self-assignment as no-op instead of a Fatal (#1473)

- this can help if using std algorithms that return a const reference
  such as std::min() does.

src/OpenFOAM/containers/HashTables/HashTable/HashTable.C

@@ -656,6 +656,11 @@ void Foam::HashTable<T, Key, Hash>::clearStorage()
 template<class T, class Key, class Hash>
 void Foam::HashTable<T, Key, Hash>::swap(HashTable<T, Key, Hash>& rhs)
 {
+    if (this == &rhs)
+    {
+        return;  // Self-swap is a no-op
+    }
+
     Foam::Swap(size_, rhs.size_);
     Foam::Swap(capacity_, rhs.capacity_);
     Foam::Swap(table_, rhs.table_);
@@ -665,6 +670,11 @@ void Foam::HashTable<T, Key, Hash>::swap(HashTable<T, Key, Hash>& rhs)
 template<class T, class Key, class Hash>
 void Foam::HashTable<T, Key, Hash>::transfer(HashTable<T, Key, Hash>& rhs)
 {
+    if (this == &rhs)
+    {
+        return;  // Self-assignment is a no-op
+    }
+
     clear();
     swap(rhs);
 }
@@ -759,12 +769,9 @@ void Foam::HashTable<T, Key, Hash>::operator=
     const HashTable<T, Key, Hash>& rhs
 )
 {
-    // Check for assignment to self
     if (this == &rhs)
     {
-        FatalErrorInFunction
-            << "attempted assignment to self"
-            << abort(FatalError);
+        return;  // Self-assignment is a no-op
     }
 
     if (!capacity_)
@@ -813,12 +820,9 @@ void Foam::HashTable<T, Key, Hash>::operator=
     HashTable<T, Key, Hash>&& rhs
 )
 {
-    // Check for assignment to self
     if (this == &rhs)
     {
-        FatalErrorInFunction
-            << "attempted assignment to self"
-            << abort(FatalError);
+        return;  // Self-assignment is a no-op
     }
 
     transfer(rhs);