ENH: minor improvements for plane

- comparison operator, for sorting based on the position of the origin.

- allow modification of the origin.

- zero-initialise for null constructor: base components are vectors
  and cheap to initialise.

- 'unfriend' the output operator: it uses public access methods

src/OpenFOAM/meshes/primitiveShapes/line/line.H

@@ -97,7 +97,7 @@ public:
         );
 
         //- Construct from Istream
-        inline line(Istream&);
+        inline explicit line(Istream& is);
 
 
     // Member Functions
@@ -149,7 +149,7 @@ public:
         ) const;
 
 
-    // Ostream operator
+    // IOstream operators
 
         friend Istream& operator>> <Point, PointRef>
         (

src/OpenFOAM/meshes/primitiveShapes/plane/plane.C

@@ -444,7 +444,7 @@ void Foam::plane::writeDict(Ostream& os) const
 }
 
 
-// * * * * * * * * * * * * * * * Friend Functions  * * * * * * * * * * * * * //
+// * * * * * * * * * * * * * * * IOstream Operators  * * * * * * * * * * * * //
 
 Foam::Ostream& Foam::operator<<(Ostream& os, const plane& pln)
 {

src/OpenFOAM/meshes/primitiveShapes/plane/plane.H

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2004-2010, 2017-2018 OpenCFD Ltd.
+    \\  /    A nd           | Copyright (C) 2004-2010, 2017-2019 OpenCFD Ltd.
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
                             | Copyright (C) 2011-2016 OpenFOAM Foundation
@@ -82,11 +82,6 @@ SourceFiles
 namespace Foam
 {
 
-// Forward Declarations
-class plane;
-Ostream& operator<<(Ostream& os, const plane& pln);
-
-
 /*---------------------------------------------------------------------------*\
                             Class plane Declaration
 \*---------------------------------------------------------------------------*/
@@ -177,7 +172,7 @@ public:
 
     // Constructors
 
-        //- Construct null. Does not set normal and point.
+        //- Construct zero-initialised.
         inline plane();
 
         //- Construct from normal vector through the origin.
@@ -221,9 +216,12 @@ public:
         //- The plane unit normal
         inline const vector& normal() const;
 
-        //- The plane base point (same as refPoint)
+        //- The plane base point
         inline const point& origin() const;
 
+        //- The plane base point, for modification
+        inline point& origin();
+
         //- The plane base point (same as origin)
         inline const point& refPoint() const;
 
@@ -293,21 +291,26 @@ public:
 
         //- Write to dictionary
         void writeDict(Ostream& os) const;
-
-
-    // IOstream Operators
-
-        //- Write plane properties
-        friend Ostream& operator<<(Ostream& os, const plane& pln);
-
 };
 
 
+// IOstream Operators
+
+//- Write plane normal, origin
+Ostream& operator<<(Ostream& os, const plane& pln);
+
+
 // Global Operators
 
+//- Test for equality of origin and normal
 inline bool operator==(const plane& a, const plane& b);
+
+//- Test for inequality of origin or normal
 inline bool operator!=(const plane& a, const plane& b);
 
+//- Compare origin
+inline bool operator<(const plane& a, const plane& b);
+
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 

src/OpenFOAM/meshes/primitiveShapes/plane/planeI.H

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+    \\  /    A nd           | Copyright (C) 2018-2019 OpenCFD Ltd.
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -26,6 +26,9 @@ License
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 inline Foam::plane::plane()
+:
+    normal_(Zero),
+    origin_(Zero)
 {}
 
 
@@ -43,6 +46,12 @@ inline const Foam::point& Foam::plane::origin() const
 }
 
 
+inline Foam::point& Foam::plane::origin()
+{
+    return origin_;
+}
+
+
 inline const Foam::point& Foam::plane::refPoint() const
 {
     return origin_;
@@ -103,4 +112,10 @@ inline bool Foam::operator!=(const plane& a, const plane& b)
 }
 
 
+inline bool Foam::operator<(const plane& a, const plane& b)
+{
+    return (a.origin() < b.origin());
+}
+
+
 // ************************************************************************* //