ENH: add (C++11) user-literal for degrees to radians conversion

- Programming convenience.
  Eg, cos(45_deg) vs cos(degToRad(45))

STYLE: conversions marked as constexpr and noexcept

applications/test/unitConversion/Make/files

@@ -0,0 +1,3 @@
+Test-unitConversion.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-unitConversion

applications/test/unitConversion/Test-unitConversion.C

@@ -0,0 +1,50 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2017 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Application
+    Test-unitConversion
+
+\*---------------------------------------------------------------------------*/
+
+#include "IOstreams.H"
+#include "unitConversion.H"
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+//  Main program:
+
+int main(int argc, char *argv[])
+{
+    Info<< "30_deg:   " << 30_deg << nl;
+    Info<< "30.0_deg: " << 30.0_deg << nl;
+    Info<< "3e+1_deg: " << 3e+1_deg << nl;
+    Info<< "degToRad(30): " << degToRad(30) << nl;
+
+    Info<< "cos(30_deg): " << ::cos(30_deg) << nl;
+
+    return 0;
+}
+
+
+// ************************************************************************* //

src/OpenFOAM/global/unitConversion/unitConversion.H

@@ -42,29 +42,43 @@ namespace Foam
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 //- Conversion from degrees to radians
-inline scalar degToRad(const scalar deg)
+inline constexpr scalar degToRad(const scalar deg) noexcept
 {
-    return (deg*constant::mathematical::pi/180.0);
+    return (deg*Foam::constant::mathematical::pi/180.0);
 }
 
 //- Conversion from radians to degrees
-inline scalar radToDeg(const scalar rad)
+inline constexpr scalar radToDeg(const scalar rad) noexcept
 {
-    return (rad*180.0/constant::mathematical::pi);
+    return (rad*180.0/Foam::constant::mathematical::pi);
 }
 
 //- Conversion from atm to Pa
-inline scalar atmToPa(const scalar atm)
+inline constexpr scalar atmToPa(const scalar atm) noexcept
 {
     return (atm*101325.0);
 }
 
 //- Conversion from atm to Pa
-inline scalar paToAtm(const scalar pa)
+inline constexpr scalar paToAtm(const scalar pa) noexcept
 {
     return (pa/101325.0);
 }
 
+
+//- User literal for degrees to radians conversion (integers)
+inline constexpr scalar operator "" _deg(unsigned long long int deg) noexcept
+{
+    return (deg*Foam::constant::mathematical::pi/180.0);
+}
+
+//- User literal for degrees to radians conversion (floats)
+inline constexpr scalar operator "" _deg(long double deg) noexcept
+{
+    return (deg*Foam::constant::mathematical::pi/180.0);
+}
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace Foam