fix tuple return issues

modules/python/config/dnn_tracker.json

@@ -1 +1,7 @@
-{"ignored_headers": [], "ignored_classes": [], "user_defined_headers": [], "classes": {}, "enums": {}}
+{
+  "ignored_headers": [],
+  "ignored_classes": [],
+  "user_defined_headers": [],
+  "classes": {},
+  "enums": {}
+}

modules/python/config/gui.json

@@ -1 +1,7 @@
-{}
+{
+  "ignored_headers": [],
+  "ignored_classes": [],
+  "user_defined_headers": [],
+  "classes": {},
+  "enums": {}
+}

modules/python/config/imgproc.json

@@ -1,3 +1,7 @@
 {
-
-}
+  "ignored_headers": [],
+  "ignored_classes": [],
+  "user_defined_headers": [],
+  "classes": {},
+  "enums": {}
+}

modules/python/config/tt.json

@@ -1 +1,7 @@
-{"ignored_headers": [], "ignored_classes": [], "user_defined_headers": [], "classes": {}, "enums": {}}
+{
+  "ignored_headers": [],
+  "ignored_classes": [],
+  "user_defined_headers": [],
+  "classes": {},
+  "enums": {}
+}

modules/python/config/tt_mi.json

@@ -1 +1,11 @@
-{"ignored_headers": [], "ignored_classes": [], "user_defined_headers": [], "classes": {}, "enums": {}}
+{
+  "ignored_headers": [],
+  "ignored_classes": [],
+  "user_defined_headers": [],
+  "classes": {
+    "vpTemplateTrackerMI": {
+      "is_virtual": true
+    }
+  },
+  "enums": {}
+}

modules/python/docs/todos.rst

@@ -54,6 +54,18 @@ To be written:
 * In code documentation for the generator
 * Document config files
 
+* Failure cases
+
+  *  If you have this error:
+      error: invalid new-expression of abstract class type ‘vpTemplateTrackerMI’
+      return new Class{std::forward<Args>(args)...};
+      In file included from /home/sfelton/software/visp_build/modules/python/bindings/src/tt_mi.cpp:13:0:
+      /home/sfelton/software/visp-sfelton/modules/tracker/tt_mi/include/visp3/tt_mi/vpTemplateTrackerMI.h:46:19: note:   because the following virtual functions are pure within ‘vpTemplateTrackerMI’:
+      class VISP_EXPORT vpTemplateTrackerMI : public vpTemplateTracker
+    You should define the class (here vpTemplaterMI) as pure virtual in the config file (via the flag is_virtual)
+    This error occurs because some methods are defined as pure virtual in a parent class and are not defined in the class this class: Pure virtual class detection does not look in the class hierarchy but only at the present class
+
+
 
 Packaging
 ------------------

modules/python/generator/visp_python_bindgen/methods.py

@@ -256,12 +256,16 @@ def define_method(method: types.Method, method_config: Dict, is_class_method, sp
   else:
     self_param_with_name = None
     method_caller = bound_object.cpp_name + '::' if is_class_method else bound_object.cpp_name
+  output_param_symbols = []
   if return_type is None or return_type == 'void':
     maybe_get_return = ''
-    maybe_return_in_tuple = ''
+    output_param_symbols.append('')
   else:
     maybe_get_return = f'{return_type} res = '
-    maybe_return_in_tuple = 'res, '
+    if '&' in return_type:
+      output_param_symbols.append('&res')
+    else:
+      output_param_symbols.append('res')
 
   if len(output_param_names) == 0 and (return_type is None or return_type == 'void'):
     return_str = ''
@@ -270,7 +274,11 @@ def define_method(method: types.Method, method_config: Dict, is_class_method, sp
   elif len(output_param_names) == 1 and (return_type is None or return_type == 'void'):
     return_str = output_param_names[0]
   else:
-    return_str = f'std::make_tuple({maybe_return_in_tuple}{", ".join(output_param_names)})'
+    # When returning a tuple we need to explicitely convert references to pointer.
+    # This is required since std::tuple will upcast the ref to its base class and try to store a copy of the object
+    # If a class is pure virtual, this is not possible and will a compilation error!
+    output_param_symbols.extend(['&' + name for name in output_param_names if '&' in name])
+    return_str = f'std::make_tuple({", ".join(output_param_symbols)})'
 
   lambda_body = f'''
     {param_declarations}