Update: Using C++26 with contracts enabled

cmake/CourseExercise.cmake

@@ -21,7 +21,7 @@ function(add_course_exercise)
     endif()
 
     if(NOT EXERCISE_STANDARD)
-        set(EXERCISE_STANDARD 23)
+        set(EXERCISE_STANDARD 26)
     endif()
 
     set(target_name "${EXERCISE_MODULE}_${EXERCISE_NAME}")
@@ -33,6 +33,11 @@ function(add_course_exercise)
             "${CMAKE_CURRENT_SOURCE_DIR}/include"
     )
     course_set_cxx_standard(${target_name} ${EXERCISE_STANDARD})
+
+    if(EXERCISE_STANDARD GREATER_EQUAL 26)
+        course_enable_contracts(${target_name})
+    endif()
+
     course_apply_warnings(${target_name})
 
     if(COURSE_BUILD_TESTS)

cmake/CourseOptions.cmake

@@ -23,3 +23,22 @@ endfunction()
 function(course_set_cxx_standard target_name standard)
     target_compile_features(${target_name} PRIVATE cxx_std_${standard})
 endfunction()
+
+function(course_enable_contracts target_name)
+    if(NOT COURSE_ENABLE_CONTRACTS)
+        return()
+    endif()
+
+    if(NOT (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 16))
+        return()
+    endif()
+
+    target_compile_options(
+        ${target_name}
+        PRIVATE
+            -fcontracts
+            -fcontract-evaluation-semantic=enforce
+    )
+    target_link_options(${target_name} PRIVATE -fcontracts)
+    target_link_libraries(${target_name} PRIVATE course_contract_support)
+endfunction()