added change_observer

Author: dk949

.gitmodules

@@ -40,3 +40,6 @@
 [submodule "include/add_noexcept/include/ut/add_noexcept"]
 	path = include/add_noexcept/include/ut/add_noexcept
 	url = https://gist.github.com/dk949/d3e0628ee5768bc65c474ec370d77f55
+[submodule "include/change_observer/include/ut/change_observer"]
+	path = include/change_observer/include/ut/change_observer
+	url = https://gist.github.com/dk949/2508ff2b4b5ddf152e7b6c027e8f13c4

include/change_observer/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.21)
+project(libut LANGUAGES CXX)
+
+add_library(libut_target_change_observer INTERFACE)
+target_sources(libut_target_change_observer PUBLIC
+    FILE_SET HEADERS
+    BASE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/include
+    FILES
+        ${CMAKE_CURRENT_SOURCE_DIR}/include/ut/change_observer/change_observer.hpp
+)
+
+message(STATUS "libut: adding UT::change_observer")
+add_library(UT::change_observer ALIAS libut_target_change_observer)
+