Set reasonable defaults for caching behavior

src/ifcgeom/IfcGeom.h

@@ -46,7 +46,9 @@
 #include "../ifcgeom/IfcRepresentationShapeItem.h"
 #include "../ifcgeom/IfcGeomShapeType.h"
 
-#define NO_CACHE
+// Define this in case you want to conserve memory usage at all cost. This has been
+// benchmarked extensively: https://github.com/IfcOpenShell/IfcOpenShell/pull/47
+// #define NO_CACHE
 
 #ifdef NO_CACHE
 

src/ifcgeom/IfcGeomIterator.h

@@ -324,8 +324,12 @@ namespace IfcGeom {
 	private:
 		// Move to the next IfcRepresentation
 		void _nextShape() {
-			if (done % 100 == 99) {
-				// kernel.purge_cache();
+			// In order to conserve memory and reduce cache insertion times, the cache is
+			// cleared after an arbitary number of processed representations. This has been
+			// benchmarked extensively: https://github.com/IfcOpenShell/IfcOpenShell/pull/47
+			static const int clear_interval = 64;
+			if (done % clear_interval == clear_interval - 1) {
+				kernel.purge_cache();
 			}
 			ifcproducts.reset();
 			++ representation_iterator;