https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109464
Bug ID: 109464 Summary: gcc does not instantiate constructor for explicitly instantiated template Product: gcc Version: 12.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: lh_mouse at 126 dot com Target Milestone: --- Created attachment 54824 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54824&action=edit unreduced testcase Attached is a preprocessed file. I don't know how to reduce it for absence of a function. ``` template<typename charT> class basic_shallow_string { static_assert(!is_array<charT>::value, "invalid character type"); static_assert(is_trivial<charT>::value, "characters must be trivial"); template<typename, typename> friend class basic_cow_string; private: const charT* m_ptr; size_t m_len; public: explicit constexpr basic_shallow_string(const charT* ptr) noexcept : m_ptr(ptr), m_len(noadl::xstrlen(ptr)) { } public: constexpr const charT* c_str() const noexcept { return this->m_ptr; } constexpr size_t length() const noexcept { return this->m_len; } (... more member functions follow ...) }; extern template class basic_shallow_string<char>; ``` And in 'cow_string.cpp' I have ``` #include "cow_string.hpp" namespace rocket { template class basic_shallow_string<char>; (... more explicit instantiations follow ...) } // namespace rocket ``` This explicit instantiation instantiates all inline member functions above, but not the constructor. I have examined assembly output, and there is no constructor. Unless optimization is enabled, this causes undefined references: ``` /usr/bin/ld: asteria/repl/bin_asteria-commands.o: in function `rocket::basic_shallow_string<char> rocket::sref<char>(char const*)': /home/lh_mouse/GitHub/asteria/asteria/repl/../../rocket/cow_string.hpp:97: undefined reference to `rocket::basic_shallow_string<char>::basic_shallow_string(char const*)' collect2: error: ld returned 1 exit status ``` This happens only with the constructor.