From 811fa7f8726dd9e9f013ae9a277a6e0533a7697b Mon Sep 17 00:00:00 2001
From: Maxim Pashchenkov <maxim.pashchenkov@intel.com>
Date: Wed, 6 May 2020 15:36:56 +0300
Subject: [PATCH] Problem with substitution

---
 modules/gapi/include/opencv2/gapi/gmat.hpp            |  2 +-
 modules/gapi/include/opencv2/gapi/opencv_includes.hpp |  2 +-
 modules/gapi/include/opencv2/gapi/own/cvdefs.hpp      | 11 +++++++++--
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/modules/gapi/include/opencv2/gapi/gmat.hpp b/modules/gapi/include/opencv2/gapi/gmat.hpp
index 91f6332a1060..438a663170df 100644
--- a/modules/gapi/include/opencv2/gapi/gmat.hpp
+++ b/modules/gapi/include/opencv2/gapi/gmat.hpp
@@ -209,7 +209,7 @@ static inline GMatDesc empty_gmat_desc() { return GMatDesc{-1,-1,{-1,-1}}; }
 GAPI_EXPORTS GMatDesc descr_of(const cv::UMat &mat);
 #endif // !defined(GAPI_STANDALONE)
 
-GAPI_EXPORTS GMatDesc descr_of(const cv::Mat &mat);
+GAPI_EXPORTS GMatDesc descr_of(const cv::Mat &mat); //another way: previous declaration
 /** @} */
 
 // FIXME: WHY??? WHY it is under different namespace?
diff --git a/modules/gapi/include/opencv2/gapi/opencv_includes.hpp b/modules/gapi/include/opencv2/gapi/opencv_includes.hpp
index 5acf28023d07..767346659f67 100644
--- a/modules/gapi/include/opencv2/gapi/opencv_includes.hpp
+++ b/modules/gapi/include/opencv2/gapi/opencv_includes.hpp
@@ -9,7 +9,7 @@
 #ifndef OPENCV_GAPI_OPENCV_INCLUDES_HPP
 #define OPENCV_GAPI_OPENCV_INCLUDES_HPP
 
-#if !defined(GAPI_STANDALONE)
+#if !defined(GAPI_STANDALONE) //
 #  include <opencv2/core/mat.hpp>
 #  include <opencv2/core/cvdef.h>
 #  include <opencv2/core/types.hpp>
diff --git a/modules/gapi/include/opencv2/gapi/own/cvdefs.hpp b/modules/gapi/include/opencv2/gapi/own/cvdefs.hpp
index 008cdd6f7af0..ecf67282275d 100644
--- a/modules/gapi/include/opencv2/gapi/own/cvdefs.hpp
+++ b/modules/gapi/include/opencv2/gapi/own/cvdefs.hpp
@@ -11,13 +11,12 @@
 #if defined(GAPI_STANDALONE)
 #include <opencv2/gapi/own/types.hpp> // cv::gapi::own::Rect/Size/Point
 #include <opencv2/gapi/own/scalar.hpp> // cv::gapi::own::Scalar
-
+#include <opencv2/gapi/gmat.hpp> // call opencv_includes.hpp, that call cvdefs.hpp, that call gmat.hpp, ... 
 // Simulate OpenCV definitions taken from various
 // OpenCV interface headers if G-API is built in a
 // standalone mode.
 
 // interface.h:
-
 typedef unsigned char uchar;
 typedef          char schar;
 
@@ -139,15 +138,23 @@ enum InterpolationFlags{
     INTER_LINEAR_EXACT   = 5,
     INTER_MAX            = 7,
 };
+
+// struct GMatDesc; // another way - without include gmat.hpp
+
 // replacement of cv's structures:
 namespace gapi { namespace own {
 class Mat;
+// GMatDesc descr_of(const Mat &mat); // another way: error-> conflicts with a previous declaration in gmat.hpp 
 }} // namespace gapi::own
+
+using gapi::own::descr_of; // with include gmat.hpp it has not been declared
+
 using Rect   = gapi::own::Rect;
 using Size   = gapi::own::Size;
 using Point  = gapi::own::Point;
 using Scalar = gapi::own::Scalar;
 using Mat    = gapi::own::Mat;
+
 } // namespace cv
 
 static inline int cvFloor( double value )