Use inheritance rather than composition for QgsReferencedGeometries

See #4720 (comment)
for discussion of the rationale

Author: nyalldawson

python/core/geometry/qgsrectangle.sip

@@ -42,6 +42,8 @@ Construct a rectangle from a QRectF. The rectangle is normalized after construct
 Copy constructor
 %End
 
+    ~QgsRectangle();
+
     void set( const QgsPointXY &p1, const QgsPointXY &p2 );
 %Docstring
  Sets the rectangle from two QgsPoints. The rectangle is

python/core/geometry/qgsreferencedgeometry.sip

@@ -9,38 +9,27 @@
 
 
 
-template<T>
-class QgsReferencedGeometryPrimitive
+class QgsReferencedGeometryBase
 {
 %Docstring
- A template based class for storing geometry primitives with an associated reference system.
+ A base class for geometry primitives which are stored with an associated reference system.
 
- QgsReferencedGeometryPrimitive classes represent some form of geometry primitive
+ QgsReferencedGeometryBase classes represent some form of geometry primitive
  (such as rectangles) which have an optional coordinate reference system
  associated with them.
 
 .. versionadded:: 3.0
 .. seealso:: QgsReferencedRectangle
-.. note::
-
-   Not available in Python bindings (although SIP file is present for specific implementations).
 %End
 
 %TypeHeaderCode
 #include "qgsreferencedgeometry.h"
 %End
   public:
 
-    QgsReferencedGeometryPrimitive( T primitive, const QgsCoordinateReferenceSystem &crs = QgsCoordinateReferenceSystem() );
-%Docstring
- Constructor for QgsReferencedGeometryPrimitive, for the specified ``primitive`` and ``crs``.
-%End
-
-
-    T &primitive();
+    QgsReferencedGeometryBase( const QgsCoordinateReferenceSystem &crs = QgsCoordinateReferenceSystem() );
 %Docstring
- Returns the geometry primitive.
- :rtype: T
+ Constructor for QgsReferencedGeometryBase, with the specified ``crs``.
 %End
 
     QgsCoordinateReferenceSystem crs() const;
@@ -60,11 +49,7 @@ class QgsReferencedGeometryPrimitive
 
 };
 
-
-
-typedef QgsReferencedGeometryPrimitive<QgsRectangle> QgsReferencedGeometryPrimitiveQgsRectangleBase;
-
-class QgsReferencedRectangle : QgsReferencedGeometryPrimitiveQgsRectangleBase
+class QgsReferencedRectangle : QgsRectangle, QgsReferencedGeometryBase
 {
 %Docstring
  A QgsRectangle with associated coordinate reference system.
@@ -73,20 +58,33 @@ class QgsReferencedRectangle : QgsReferencedGeometryPrimitiveQgsRectangleBase
 
 %TypeHeaderCode
 #include "qgsreferencedgeometry.h"
-typedef QgsReferencedGeometryPrimitive<QgsRectangle> QgsReferencedGeometryPrimitiveQgsRectangleBase;
 %End
   public:
 
-    QgsReferencedRectangle( const QgsRectangle &rect );
+    QgsReferencedRectangle( const QgsRectangle &rectangle, const QgsCoordinateReferenceSystem &crs );
+%Docstring
+ Constructor for QgsReferencedRectangle, with the specified initial ``rectangle``
+ and ``crs``.
+%End
+
+};
+
+class QgsReferencedPointXY : QgsPointXY, QgsReferencedGeometryBase
+{
 %Docstring
- Construct a default optional expression.
- It will be disabled and with an empty expression.
+ A QgsPointXY with associated coordinate reference system.
+.. versionadded:: 3.0
 %End
 
-    QgsRectangle &rect();
+%TypeHeaderCode
+#include "qgsreferencedgeometry.h"
+%End
+  public:
+
+    QgsReferencedPointXY( const QgsPointXY &point, const QgsCoordinateReferenceSystem &crs );
 %Docstring
- Returns the rectangles
- :rtype: QgsRectangle
+ Constructor for QgsReferencedPointXY, with the specified initial ``point``
+ and ``crs``.
 %End
 
 };

src/core/CMakeLists.txt

@@ -447,6 +447,7 @@ SET(QGIS_CORE_SRCS
   geometry/qgspoint.cpp
   geometry/qgspolygon.cpp
   geometry/qgsrectangle.cpp
+  geometry/qgsreferencedgeometry.cpp
   geometry/qgsregularpolygon.cpp
   geometry/qgstriangle.cpp
   geometry/qgswkbptr.cpp

src/core/geometry/qgsrectangle.h

@@ -47,6 +47,11 @@ class CORE_EXPORT QgsRectangle
     //! Copy constructor
     QgsRectangle( const QgsRectangle &other );
 
+    // IMPORTANT - while QgsRectangle is inherited by QgsReferencedRectangle, we do NOT want a virtual destructor here
+    // because this class MUST be lightweight and we don't want the cost of the vtable here.
+    // see https://github.com/qgis/QGIS/pull/4720#issuecomment-308652392
+    ~QgsRectangle() = default;
+
     /**
      * Sets the rectangle from two QgsPoints. The rectangle is
      * normalised after construction.

src/core/geometry/qgsreferencedgeometry.cpp

@@ -0,0 +1,32 @@
+/***************************************************************************
+                             qgsreferencedgeometry.cpp
+                             ------------------------
+    begin                : June 2017
+    copyright            : (C) 2017 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program 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 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsreferencedgeometry.h"
+
+QgsReferencedGeometryBase::QgsReferencedGeometryBase( const QgsCoordinateReferenceSystem &crs )
+  : mCrs( crs )
+{}
+
+QgsReferencedRectangle::QgsReferencedRectangle( const QgsRectangle &rect, const QgsCoordinateReferenceSystem &crs )
+  : QgsRectangle( rect )
+  , QgsReferencedGeometryBase( crs )
+{}
+
+QgsReferencedPointXY::QgsReferencedPointXY( const QgsPointXY &point, const QgsCoordinateReferenceSystem &crs )
+  : QgsPointXY( point )
+  , QgsReferencedGeometryBase( crs )
+{}

src/core/geometry/qgsreferencedgeometry.h

@@ -25,40 +25,25 @@
 #include "qgsrectangle.h"
 
 /**
- * \class QgsReferencedGeometryPrimitive
+ * \class QgsReferencedGeometryBase
  * \ingroup core
- * A template based class for storing geometry primitives with an associated reference system.
+ * A base class for geometry primitives which are stored with an associated reference system.
  *
- * QgsReferencedGeometryPrimitive classes represent some form of geometry primitive
+ * QgsReferencedGeometryBase classes represent some form of geometry primitive
  * (such as rectangles) which have an optional coordinate reference system
  * associated with them.
  *
  * \since QGIS 3.0
  * \see QgsReferencedRectangle
- * \note Not available in Python bindings (although SIP file is present for specific implementations).
  */
-template<typename T>
-class CORE_EXPORT QgsReferencedGeometryPrimitive
+class CORE_EXPORT QgsReferencedGeometryBase
 {
   public:
 
     /**
-     * Constructor for QgsReferencedGeometryPrimitive, for the specified \a primitive and \a crs.
+     * Constructor for QgsReferencedGeometryBase, with the specified \a crs.
      */
-    QgsReferencedGeometryPrimitive( T primitive, const QgsCoordinateReferenceSystem &crs = QgsCoordinateReferenceSystem() )
-      : mPrimitive( primitive )
-      , mCrs( crs )
-    {}
-
-    /**
-     * Returns the geometry primitive.
-     */
-    T primitive() const { return mPrimitive; } SIP_SKIP
-
-    /**
-     * Returns the geometry primitive.
-     */
-    T &primitive() { return mPrimitive; }
+    QgsReferencedGeometryBase( const QgsCoordinateReferenceSystem &crs = QgsCoordinateReferenceSystem() );
 
     /**
      * Returns the associated coordinate reference system, or an invalid CRS if
@@ -76,32 +61,41 @@ class CORE_EXPORT QgsReferencedGeometryPrimitive
 
   private:
 
-    T mPrimitive;
     QgsCoordinateReferenceSystem mCrs;
 
 };
 
-//template class  QgsReferencedGeometryPrimitive< QgsRectangle > QgsReferencedRectangle;
-
 /**
  * \ingroup core
  * A QgsRectangle with associated coordinate reference system.
  * \since QGIS 3.0
  */
-class CORE_EXPORT QgsReferencedRectangle : public QgsReferencedGeometryPrimitive< QgsRectangle >
+class CORE_EXPORT QgsReferencedRectangle : public QgsRectangle, public QgsReferencedGeometryBase
 {
   public:
 
     /**
-     * Construct a default optional expression.
-     * It will be disabled and with an empty expression.
+     * Constructor for QgsReferencedRectangle, with the specified initial \a rectangle
+     * and \a crs.
      */
-    QgsReferencedRectangle( const QgsRectangle &rect ) : QgsReferencedGeometryPrimitive( rect ) {}
+    QgsReferencedRectangle( const QgsRectangle &rectangle, const QgsCoordinateReferenceSystem &crs );
+
+};
+
+/**
+ * \ingroup core
+ * A QgsPointXY with associated coordinate reference system.
+ * \since QGIS 3.0
+ */
+class CORE_EXPORT QgsReferencedPointXY : public QgsPointXY, public QgsReferencedGeometryBase
+{
+  public:
 
     /**
-     * Returns the rectangles
+     * Constructor for QgsReferencedPointXY, with the specified initial \a point
+     * and \a crs.
      */
-    QgsRectangle &rect() { return primitive(); }
+    QgsReferencedPointXY( const QgsPointXY &point, const QgsCoordinateReferenceSystem &crs );
 
 };
 

src/core/qgspointxy.h

@@ -91,8 +91,10 @@ class CORE_EXPORT QgsPointXY
      */
     QgsPointXY( const QgsPoint &point );
 
-    ~QgsPointXY()
-    {}
+    // IMPORTANT - while QgsPointXY is inherited by QgsReferencedPointXY, we do NOT want a virtual destructor here
+    // because this class MUST be lightweight and we don't want the cost of the vtable here.
+    // see https://github.com/qgis/QGIS/pull/4720#issuecomment-308652392
+    ~QgsPointXY() = default;
 
     /** Sets the x value of the point
      * \param x x coordinate