[multibody] [addFrame] Change return type to FrameIndex

src/multibody/model.hpp

@@ -508,9 +508,8 @@ namespace pinocchio
     /// \param[in] frame The frame to add to the kinematic tree.
     ///
     /// \return Returns the index of the frame if it has been successfully added or if it already exists in the kinematic tree.
-    ///         The function returns -1 when the frame.type did not match with the existing frame in the kinematic having the same name.
     ///
-    int addFrame(const Frame & frame);
+    FrameIndex addFrame(const Frame & frame);
 
     ///
     /// \brief Check the validity of the attributes of Model with respect to the specification of some

src/multibody/model.hxx

@@ -248,19 +248,19 @@ namespace pinocchio
   }
 
   template<typename Scalar, int Options, template<typename,int> class JointCollectionTpl>
-  inline int ModelTpl<Scalar,Options,JointCollectionTpl>::
+  inline typename ModelTpl<Scalar,Options,JointCollectionTpl>::FrameIndex
+  ModelTpl<Scalar,Options,JointCollectionTpl>::
   addFrame(const Frame & frame)
   {
     // Check if the frame.name exists with the same type
     if(existFrame(frame.name,frame.type))
     {
-      FrameIndex frame_id = getFrameId(frame.name,frame.type);
-      return (int)frame_id;
+      return getFrameId(frame.name,frame.type);
     }
     // else: we must add a new frames to the current stack
     frames.push_back(frame);
     nframes++;
-    return nframes - 1;
+    return FrameIndex(nframes - 1);
   }
   
   template<typename Scalar, int Options, template<typename,int> class JointCollectionTpl>