diff --git a/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H b/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H
index 804ae898cb..5dbde12568 100644
--- a/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H
+++ b/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H
@@ -181,7 +181,7 @@ public:
         //  not previously exist in the set.
         bool insert(const Key& key)
         {
-            return this->parent_type::insert(key, zero::null());
+            return this->parent_type::emplace(key);
         }
 
         //- Same as insert (no value to overwrite)
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
index f7eb66957c..7634a8f50f 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
@@ -120,8 +120,8 @@ class HashTable
         typedef typename std::conditional
         <
             std::is_same<zero::null, typename std::remove_cv<T>::type>::value,
-            Detail::HashTableSingle<T, Key>,
-            Detail::HashTablePair<T, Key>
+            Detail::HashTableSingle<Key>,
+            Detail::HashTablePair<Key, T>
         >::type node_type;
 
 
@@ -323,7 +323,7 @@ public:
         ) const;
 
 
-      // Counting
+    // Counting
 
         //- Count the number of keys that satisfy the unary predicate
         //  \param invert changes the logic to select when the predicate
@@ -835,7 +835,7 @@ public:
         };
 
 
-    //- Iterating over keys only
+    // Iterator (keys)
 
         //- An iterator wrapper for returning a reference to the key
         template<class Iter>
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H b/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
index 84d41e678d..ccf53888ff 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
@@ -56,17 +56,14 @@ namespace Detail
                           Class isPointer Declaration
 \*---------------------------------------------------------------------------*/
 
-//- Test for pointer-like behaviour
-template<class T>
-struct isPointer : public std::is_pointer<T> {};
+//- Pointer-like behaviour
+template<class T> struct isPointer : std::is_pointer<T> {};
 
-//- An autoPtr is pointer-like
-template<class T>
-struct isPointer<autoPtr<T>> : public std::true_type {};
+//- Pointer-like behaviour for autoPtr
+template<class T> struct isPointer<autoPtr<T>> : std::true_type {};
 
-//- A unique_ptr is pointer-like
-template<class T>
-struct isPointer<std::unique_ptr<T>> : public std::true_type {};
+//- Pointer-like behaviour for std::unique_ptr
+template<class T> struct isPointer<std::unique_ptr<T>> : std::true_type {};
 
 
 /*---------------------------------------------------------------------------*\
@@ -77,16 +74,16 @@ struct isPointer<std::unique_ptr<T>> : public std::true_type {};
 //  Structure with a (K,V) tuple and a linked-list for collisions
 //  Could store key/val as std::pair, but no particular advantage
 //  unless the iterator dereference type changes.
-template<class T, class Key>
+template<class K, class V>
 struct HashTablePair
 {
     // Types
 
         //- Type of key
-        typedef Key key_type;
+        typedef K key_type;
 
         //- Type of content
-        typedef T mapped_type;
+        typedef V mapped_type;
 
         //- This struct stores a value
         static constexpr bool stores_value()
@@ -150,7 +147,7 @@ struct HashTablePair
         }
 
         //- Write (key, val) pair - for pointer types
-        template<class TypeT = T>
+        template<class TypeT = V>
         typename std::enable_if<Detail::isPointer<TypeT>::value, void>::type
         print(Ostream& os) const
         {
@@ -163,7 +160,7 @@ struct HashTablePair
         }
 
         //- Write (key, val) pair - for non-pointer types
-        template<class TypeT = T>
+        template<class TypeT = V>
         typename std::enable_if<!Detail::isPointer<TypeT>::value, void>::type
         print(Ostream& os) const
         {
@@ -178,13 +175,13 @@ struct HashTablePair
 
 //- Internal storage type for HashSet entries
 //  Structure with a single (K) value and a linked-list for collisions
-template<class T, class Key>
+template<class K>
 struct HashTableSingle
 {
     // Types
 
         //- Type of key
-        typedef Key key_type;
+        typedef K key_type;
 
         //- Type of content
         typedef Foam::zero::null mapped_type;
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTableI.H b/src/OpenFOAM/containers/HashTables/HashTable/HashTableI.H
index 9342a71424..d2b70816d2 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTableI.H
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTableI.H
@@ -64,7 +64,7 @@ inline bool Foam::HashTable<T, Key, Hash>::empty() const
 template<class T, class Key, class Hash>
 inline T& Foam::HashTable<T, Key, Hash>::at(const Key& key)
 {
-    const iterator iter(this->find(key));
+    iterator iter(this->find(key));
 
     if (!iter.good())
     {
@@ -166,10 +166,10 @@ template<class T, class Key, class Hash>
 inline bool Foam::HashTable<T, Key, Hash>::insert
 (
     const Key& key,
-    const T& val
+    const T& obj
 )
 {
-    return this->setEntry(false, key, val);
+    return this->setEntry(false, key, obj);
 }
 
 
@@ -177,10 +177,10 @@ template<class T, class Key, class Hash>
 inline bool Foam::HashTable<T, Key, Hash>::insert
 (
     const Key& key,
-    T&& val
+    T&& obj
 )
 {
-    return this->setEntry(false, key, std::forward<T>(val));
+    return this->setEntry(false, key, std::forward<T>(obj));
 }
 
 
@@ -188,10 +188,10 @@ template<class T, class Key, class Hash>
 inline bool Foam::HashTable<T, Key, Hash>::set
 (
     const Key& key,
-    const T& val
+    const T& obj
 )
 {
-    return this->setEntry(true, key, val);   // Overwrite
+    return this->setEntry(true, key, obj);   // Overwrite
 }
 
 
@@ -199,10 +199,10 @@ template<class T, class Key, class Hash>
 inline bool Foam::HashTable<T, Key, Hash>::set
 (
     const Key& key,
-    T&& val
+    T&& obj
 )
 {
-    return this->setEntry(true, key, std::forward<T>(val));  // Overwrite
+    return this->setEntry(true, key, std::forward<T>(obj));  // Overwrite
 }
 
 
@@ -223,48 +223,28 @@ inline const T& Foam::HashTable<T, Key, Hash>::lookup
 template<class T, class Key, class Hash>
 inline T& Foam::HashTable<T, Key, Hash>::operator[](const Key& key)
 {
-    const iterator iter(this->find(key));
-
-    if (!iter.good())
-    {
-        FatalErrorInFunction
-            << key << " not found in table.  Valid entries: "
-            << toc()
-            << exit(FatalError);
-    }
-
-    return iter.val();
+    return this->at(key);
 }
 
 
 template<class T, class Key, class Hash>
 inline const T& Foam::HashTable<T, Key, Hash>::operator[](const Key& key) const
 {
-    const const_iterator iter(this->cfind(key));
-
-    if (!iter.good())
-    {
-        FatalErrorInFunction
-            << key << " not found in table.  Valid entries: "
-            << toc()
-            << exit(FatalError);
-    }
-
-    return iter.val();
+    return this->at(key);
 }
 
 
 template<class T, class Key, class Hash>
 inline T& Foam::HashTable<T, Key, Hash>::operator()(const Key& key)
 {
-    const iterator iter(this->find(key));
+    iterator iter(this->find(key));
 
     if (iter.good())
     {
         return iter.val();
     }
 
-    this->insert(key, mapped_type());
+    this->emplace(key);
     return find(key).val();
 }
 
@@ -276,7 +256,7 @@ inline T& Foam::HashTable<T, Key, Hash>::operator()
     const T& deflt
 )
 {
-    const iterator iter(this->find(key));
+    iterator iter(this->find(key));
 
     if (iter.good())
     {