Update: Using C++26 with contracts enabled

.gitignore

@@ -1,5 +1,6 @@
 # Build directories
 build/
+build-gcc26/
 cmake-build-*/
 out/
 

CMakePresets.json

@@ -0,0 +1,58 @@
+{
+  "version": 6,
+  "cmakeMinimumRequired": {
+    "major": 3,
+    "minor": 20,
+    "patch": 0
+  },
+  "configurePresets": [
+    {
+      "name": "default",
+      "displayName": "Default (system compiler)",
+      "generator": "Unix Makefiles",
+      "binaryDir": "${sourceDir}/build",
+      "cacheVariables": {
+        "CMAKE_BUILD_TYPE": "Debug",
+        "COURSE_ENABLE_CONTRACTS": "ON"
+      }
+    },
+    {
+      "name": "gcc26-contracts",
+      "displayName": "GCC 16 + C++26 contracts (recommended)",
+      "generator": "Unix Makefiles",
+      "binaryDir": "${sourceDir}/build-gcc26",
+      "cacheVariables": {
+        "CMAKE_BUILD_TYPE": "Debug",
+        "CMAKE_C_COMPILER": "/opt/homebrew/bin/gcc-16",
+        "CMAKE_CXX_COMPILER": "/opt/homebrew/bin/g++-16",
+        "COURSE_ENABLE_CONTRACTS": "ON"
+      }
+    }
+  ],
+  "buildPresets": [
+    {
+      "name": "default",
+      "configurePreset": "default"
+    },
+    {
+      "name": "gcc26-contracts",
+      "configurePreset": "gcc26-contracts"
+    }
+  ],
+  "testPresets": [
+    {
+      "name": "default",
+      "configurePreset": "default",
+      "output": {
+        "outputOnFailure": true
+      }
+    },
+    {
+      "name": "gcc26-contracts",
+      "configurePreset": "gcc26-contracts",
+      "output": {
+        "outputOnFailure": true
+      }
+    }
+  ]
+}

cmake/toolchains/gcc-16.cmake

@@ -0,0 +1,3 @@
+# Use GCC 16 for C++26 contracts support on macOS (Homebrew).
+set(CMAKE_C_COMPILER "/opt/homebrew/bin/gcc-16" CACHE FILEPATH "C compiler")
+set(CMAKE_CXX_COMPILER "/opt/homebrew/bin/g++-16" CACHE FILEPATH "C++ compiler")

support/CMakeLists.txt

@@ -0,0 +1,8 @@
+add_library(course_contract_support STATIC contract_handler.cpp)
+target_compile_features(course_contract_support PUBLIC cxx_std_26)
+set_target_properties(course_contract_support PROPERTIES POSITION_INDEPENDENT_CODE ON)
+
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND COURSE_ENABLE_CONTRACTS)
+    target_compile_options(course_contract_support PRIVATE -fcontracts)
+    target_link_options(course_contract_support PRIVATE -fcontracts)
+endif()

support/contract_handler.cpp

@@ -0,0 +1,6 @@
+#include <contracts>
+#include <cstdlib>
+
+void handle_contract_violation(const std::contracts::contract_violation&) {
+    std::abort();
+}