diff --git a/src/OpenFOAM/primitives/ops/flipOp.C b/src/OpenFOAM/primitives/ops/flipOp.C
index 39316a03d1..a9ea570596 100644
--- a/src/OpenFOAM/primitives/ops/flipOp.C
+++ b/src/OpenFOAM/primitives/ops/flipOp.C
@@ -29,8 +29,7 @@ License
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-template<>
-Foam::scalar Foam::flipOp::operator()(const scalar& v) const
+template<> Foam::scalar Foam::flipOp::operator()(const scalar& v) const
 {
     return -v;
 }
@@ -42,7 +41,7 @@ template<> Foam::vector Foam::flipOp::operator()(const vector& v) const
 }
 
 
-template<>Foam::sphericalTensor Foam::flipOp::operator()
+template<> Foam::sphericalTensor Foam::flipOp::operator()
 (
     const sphericalTensor& v
 ) const
diff --git a/src/OpenFOAM/primitives/ops/flipOp.H b/src/OpenFOAM/primitives/ops/flipOp.H
index e1c9f1c247..b8500f6ed4 100644
--- a/src/OpenFOAM/primitives/ops/flipOp.H
+++ b/src/OpenFOAM/primitives/ops/flipOp.H
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2015-2016 OpenFOAM Foundation
+    Copyright (C) 2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -27,7 +28,7 @@ Class
     Foam::flipOp
 
 Description
-    Class containing functor to negate primitives. Dummy for all other types.
+    Functor to negate primitives. Dummy for most other types.
 
     Used in mesh transformations where face can flip.
 
@@ -50,34 +51,40 @@ namespace Foam
                            Class flipOp Declaration
 \*---------------------------------------------------------------------------*/
 
-class flipOp
+struct flipOp
 {
-public:
-
-    template<class Type>
-    Type operator()(const Type& val) const
+    template<class T>
+    T operator()(const T& val) const
     {
         return val;
     }
 };
 
 
-class noOp
+//- Pass through value. Should never be specialized.
+struct noOp
 {
-public:
-
-    template<class Type>
-    Type operator()(const Type& val) const
+    template<class T>
+    const T& operator()(const T& val) const noexcept
     {
         return val;
     }
 };
 
 
-class flipLabelOp
+//- Invert boolean value
+struct flipBoolOp
 {
-public:
+    bool operator()(const bool& val) const noexcept
+    {
+        return !val;
+    }
+};
 
+
+//- Negate integer values
+struct flipLabelOp
+{
     label operator()(const label& val) const
     {
         return -val;