Consider the example: struct Base { constexpr virtual ~Base(){} }; struct Derived: Base {}; constexpr Derived d; Destructor for the `Derived` should be implicitly defined. However the above snippet produces error message on GCC-10 with -std=c++2a flag: `error: 'virtual constexpr Derived::~Derived()' used before its definition`.
Seems to be dup of https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92695#c12 I'm afraid I don't know how to resolve this.
I just ran into this today. The referenced "dup" seems to have been resolved last June, but this is still failing. Also probably the same as https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99495. Is there any chance someone could take a fresh look at this?
*** Bug 96614 has been marked as a duplicate of this bug. ***
*** Bug 99495 has been marked as a duplicate of this bug. ***
The problem is the default Destructor in the Derived for the other examples. So this can be reduced to just: struct Base { constexpr virtual ~Base() = default; }; constexpr Base b;
*** Bug 104653 has been marked as a duplicate of this bug. ***
*** Bug 106287 has been marked as a duplicate of this bug. ***
*** Bug 105846 has been marked as a duplicate of this bug. ***
*** Bug 107512 has been marked as a duplicate of this bug. ***
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>: https://gcc.gnu.org/g:c0b38e9fec71dc4cc5e99b1f0cb159c15a8da9ba commit r13-3638-gc0b38e9fec71dc4cc5e99b1f0cb159c15a8da9ba Author: Patrick Palka <ppalka@redhat.com> Date: Thu Nov 3 14:55:35 2022 -0400 c++: constexpr error with defaulted virtual dtor [PR93413] We're rejecting the below testcase with error: 'virtual constexpr Base::~Base()' used before its definition error: 'virtual constexpr Derived::~Derived()' used before its definition due to special handling in mark_used added by r181272 to defer synthesis of virtual destructors until EOF (where we can set their linkage), which in turn makes them effectively unusable during constexpr evaluation. Fortunately it seems this special handling is unnecessary ever since r208030 enabled us to tentatively set linkage of all defaulted virtual destructors, including templated ones. So this patch gets rid of this special handling. PR c++/93413 gcc/cp/ChangeLog: * decl2.cc (mark_used): Don't defer synthesis of virtual functions. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/constexpr-virtual21.C: New test.
Fixed for GCC 13. The fix is probably unsuitable for backporting, and there are workarounds anyway -- one workaround is to turn the problematic class into a class template with an explicitly defaulted dtor, e.g. for the original testcase do: struct Base { constexpr virtual ~Base(){} }; template<class=void> struct Derived: Base { ~Derived() = default; }; constexpr Derived<> d;