https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113754
Bug ID: 113754 Summary: GCC complains when using a type that depends on lambda Product: gcc Version: 13.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: milasudril at gmail dot com Target Milestone: --- I tried to use template<typename T, auto DeleteFn> using unique_ptr_deleter = std::unique_ptr<T, decltype([](T* obj) { DeleteFn(obj); })>; As described by https://andreasfertig.blog/2022/08/cpp-insights-lambdas-in-unevaluated-contexts/ It works well as long as I do not try define it in a header file. If gcc detects a from a header file that uses unique_ptr_deleter, I get the warning lib/array_classes/./memory_block.hpp:12:8: error: 'memory_block' has a field 'unique_ptr_deleter<void, free> terraformer::memory_block::m_pointer' whose type has internal linkage [-Werror=subobject-linkage] Clang do generate any warnings. Stand-alone snippet to reproduce the issue: #include <memory> #include <cstdlib> # 7 "lib/array_classes/./memory_block.hpp" template<class T, auto DeleteFn> using unique_ptr_deleter = std::unique_ptr<T, decltype([](T* obj) { DeleteFn(obj); })>; class memory_block { public: private: unique_ptr_deleter<void, free> m_pointer; }; # 4 "lib/array_classes/memory_block.test.cpp"