C++20 -> C++23 and add Switch

CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.27)
 project(utempl
   VERSION 0.1)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
-set(CMAKE_CXX_STANDART 20)
+set(CMAKE_CXX_STANDART 23)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CXX_EXTENSIONS NO)
 set(BOOST_INCLUDE_LIBRARIES "pfr")
@@ -50,7 +50,7 @@ else()
   find_package(Boost 1.85.0 REQUIRED)
   target_link_libraries(utempl INTERFACE fmt::fmt-header-only ${Boost_LIBRARIES})
 endif()
-target_compile_features(utempl INTERFACE cxx_std_20)
+target_compile_features(utempl INTERFACE cxx_std_23)
 
 install(TARGETS utempl
   EXPORT utemplTargets
@@ -89,7 +89,7 @@ if(ENABLE_TESTS)
   file(GLOB SOURCES tests/* tests/*/* tests/*/*/*)
   add_executable(utempl_tests ${SOURCES})
   target_link_libraries(utempl_tests GTest::gtest_main utempl)
-  set_property(TARGET utempl_tests PROPERTY CXX_STANDARD 20)
+  set_property(TARGET utempl_tests PROPERTY CXX_STANDARD 23)
   include(GoogleTest)
   gtest_discover_tests(utempl_tests)
 endif()
@@ -99,7 +99,7 @@ if(ENABLE_EXAMPLES)
       get_filename_component(EXAMPLE_NAME ${EXAMPLE_SRC} NAME_WE)
       add_executable(${EXAMPLE_NAME} ${EXAMPLE_SRC})
       target_link_libraries(${EXAMPLE_NAME} utempl)
-      set_property(TARGET ${EXAMPLE_NAME} PROPERTY CXX_STANDARD 20)
+      set_property(TARGET ${EXAMPLE_NAME} PROPERTY CXX_STANDARD 23)
       set_target_properties(${EXAMPLE_NAME} PROPERTIES
           RUNTIME_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/examples/output")
 endforeach()

examples/src/switch.cpp

@@ -0,0 +1,23 @@
+#include <utempl/utils.hpp>
+
+auto main() -> int {
+  static_assert(utempl::Switch<int>(utempl::Tuple{2, 1, 0}, utempl::Tuple{0, 1, 2}, 0, [](int value) {
+                  return value + 1;
+                }) == 3);
+  static_assert(utempl::Switch<int>(utempl::Tuple{2, 1, 0}, utempl::Tuple{0, 1, 2}, 3, [](int value) {
+                  return value + 1;
+                }) == 0);
+  static_assert(utempl::Switch<std::optional<int>>(utempl::Tuple{2, 1, 0}, utempl::Tuple{0, 1, 2}, 3, [](int value) {
+                  return value + 1;
+                }) == std::nullopt);
+  static_assert(utempl::Switch<int>(
+                    utempl::Tuple{2, 1, 0},
+                    utempl::Tuple{0, 1, 2},
+                    3,
+                    [](int value) {
+                      return value + 1;
+                    },
+                    [] {
+                      return 42;
+                    }) == 42);
+};

include/utempl/utils.hpp

@@ -606,4 +606,30 @@ constexpr auto Enumerate(Tuple&& tuple) {
   });
 };
 
+template <typename T>
+constexpr auto kDefaultCreator = [] {
+  return T{};
+};
+
+template <typename R,
+          TupleLike KeysTuple,
+          TupleLike ValuesTuple,
+          typename Key,
+          typename F,
+          std::invocable Default = decltype(kDefaultCreator<R>)>
+constexpr auto Switch(KeysTuple&& keysTuple, ValuesTuple&& valuesTuple, Key&& key, F&& f, Default&& def = {}) {
+  return Unpack(std::forward<KeysTuple>(keysTuple), [&]<typename... Keys>(Keys&&... keys) {
+    return Unpack(std::forward<ValuesTuple>(valuesTuple), [&]<typename... Values>(Values&&... values) {
+      return *FirstOf(Tuple{[&] {
+                        return std::forward<Keys>(keys) == std::forward<Key>(key) ? std::forward<F>(f)(std::forward<Values>(values))
+                                                                                  : std::optional<R>{};
+                      }...},
+                      std::optional<R>{})
+                  .or_else([&] -> std::optional<R> {
+                    return std::forward<Default>(def)();
+                  });
+    });
+  });
+};
+
 }  // namespace utempl