Add constexpr check example

CMakeLists.txt

@@ -68,11 +68,13 @@ if(ENABLE_EXAMPLES)
   file(GLOB EXAMPLES_SRC "examples/src/*.cpp")
   foreach(EXAMPLE_SRC ${EXAMPLES_SRC})
       get_filename_component(EXAMPLE_NAME ${EXAMPLE_SRC} NAME_WE)
+      if(NOT ${EXAMPLE_NAME} STREQUAL "constexpr_check")
           add_executable(${EXAMPLE_NAME} ${EXAMPLE_SRC})
           target_link_libraries(${EXAMPLE_NAME} cserver)
           set_property(TARGET ${EXAMPLE_NAME} PROPERTY CXX_STANDARD 23)
           set_target_properties(${EXAMPLE_NAME} PROPERTIES
               RUNTIME_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/examples/output/")
-endforeach()
+      endif()
+  endforeach()
 endif()
 

examples/src/constexpr_check.cpp

@@ -0,0 +1,40 @@
+#include <cserver/components/loggable_component_base.hpp>
+
+
+struct SomeComponent {
+  static constexpr utempl::ConstexprString kName = "component";
+
+  constexpr SomeComponent(auto&) {};
+};
+
+
+struct SomeComponent2 {
+  static constexpr utempl::ConstexprString kName = "component2";
+
+  constexpr SomeComponent2(auto&) {};
+};
+
+struct OtherComponent {
+  static constexpr utempl::ConstexprString kName = "other";
+
+  auto Foo(auto& context) -> void {
+    context.template FindComponent<"component2">(); // UB on runtime with old check
+                                                    // Compile time error with new check(check via loopholes)
+  };
+
+  constexpr OtherComponent(auto& context) {
+    context.template FindComponent<"component">();
+    Foo(context);
+  };
+};
+
+
+auto main() -> int {
+  cserver::ServiceContextBuilder{}
+    .AppendConfigParam<"threads", 8>()
+    .Append<SomeComponent>()
+    .Append<SomeComponent2>()
+    .Append<OtherComponent>()
+    .Sort()
+  .Run();
+};