added run time polymorphism test file

Makefile

@@ -127,7 +127,7 @@ newtests: newtests_before
 
 .PHONY: pretest test test2 nobuild
 
-test: pretest test2 nobuild
+test: pretest test2 nobuild test_rtp
 	@echo "-done target $@"
 
 test2: test_SY test_SN test_single test_multiple
@@ -211,6 +211,14 @@ test_bg_1: BUILD/bg_test_1 buildf
 BUILD/bg_test_1: misc/test_files/bg_test_1.cpp homog2d.hpp Makefile buildf
 	$(CXX) $(CXXFLAGS) -O2 -o $@ $< $(LDFLAGS)
 
+test_rtp: BUILD/homog2d_test_rtp
+	@echo "-Running RTP test:"
+	@BUILD/homog2d_test_rtp
+
+
+BUILD/homog2d_test_rtp: misc/homog2d_test_rtp.cpp homog2d.hpp buildf
+	$(CXX) $(CXXFLAGS) -O2 -o $@ $< $(LDFLAGS) 2>BUILD/homog2d_test_rtp.stderr
+
 #=======================================================================
 # speed test
 speed_test: speed_test_b

docs/homog2d_manual.md

@@ -640,7 +640,7 @@ Check [this section](#frect_union) about union and intersection area of two rect
 <a id="p_circle"></a>
 
 These are modeled by their center point and radius.
-Creation is straightforward, whathever your needs:
+Creation is straightforward, whatever your needs:
 ```C++
 Circle c1;                          // at (0,0), radius = 1
 Circle c2( center_point );          // radius = 1

misc/homog2d_test_rtp.cpp

@@ -0,0 +1,52 @@
+/**************************************************************************
+
+    This file is part of the C++ library "homog2d", dedicated to
+    handle 2D lines and points, see https://github.com/skramm/homog2d
+
+    Author & Copyright 2019-2023 Sebastien Kramm
+
+    Contact: [email protected]
+
+    Licence: MPL v2
+
+	This Source Code Form is subject to the terms of the Mozilla Public
+	License, v. 2.0. If a copy of the MPL was not distributed with this
+	file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+**************************************************************************/
+
+/**
+\file homog2d_test_rtp.cpp
+\brief This program will test the RunTime Polymorphism capabilities
+*/
+
+
+#define CATCH_CONFIG_RUNNER   // alternative: main provided here
+#include "catch.hpp"
+
+#define HOMOG2D_TEST_MODE
+#define HOMOG2D_ENABLE_RTP
+#include "../homog2d.hpp"
+
+using namespace h2d;
+
+int main( int, char*)
+{
+	Segment seg;
+	CPolyline pol;
+	Circle cir;
+	FRect rect;
+	std::vector<std::shared_ptr<detail::Root>> vec;
+	vec.push_back( std::make_shared<Circle>(cir) );
+	vec.push_back( std::make_shared<CPolyline>(pol) );
+	vec.push_back( std::make_shared<Segment>(seg) );
+	vec.push_back( std::make_shared<FRect>(rect) );
+
+	for( auto& e: vec )
+	{
+		std::cout << getString(e->type()) << ": " << *e
+			<< "\n  -area = " << e->area()
+			<< "\n  -length = " << e->length()
+			<< '\n';
+	}
+}

misc/no_build/no_build_18.cxx

@@ -0,0 +1,4 @@
+// Polyline: cannot create an open polyline as a RCP
+
+	OPolyline op(4,5);
+

misc/no_build/no_build_19.cxx

@@ -0,0 +1,7 @@
+// make sure that translate() requires numeric values
+
+	Circle c1;
+	FRect r;
+	r.translate( c1, 3 );
+
+