Or a flag is stored, whether the object a has been destructed.   -----Ursprüngliche Nachricht----- Von:Zhihao Yuan via Std-Proposals <std-proposals_at_[hidden]> Gesendet:Do 11.12.2025 23:59 Betreff:Re: [std-proposals] [PXXXXR0] Add a New Keyword `undecl` Anlage:signature.asc An:std-proposals_at_[hidden]; CC:Zhihao Yuan <zy_at_[hidden]>; On Tuesday, December 9th, 2025 at 5:35 PM, Breno Guimarães via Std-Proposals <std-proposals_at_[hidden]> wrote: The paper says that undecl can only be called in the same brace level as the declaration. So I guess this example isn't valid.  So at least the list of destructors to call during stack unwinding isn't dynamic :)  But question remains. Consider    vector a = f1();   vector b = f2();    foo(); // throw?   undecl a;   undecl b;  If foo() does not throw, presumably we destruct a then b; if it throws, we then destruct b then a? Besides, I'm not sure whether the first case is implementable in all unwinding ABIs. Please check with implementers.  -- Zhihao Yuan, ID lichray The best way to predict the future is to invent it. _______________________________________________ Em ter., 9 de dez. de 2025, 22:29, Sebastian Wittmeier via Std-Proposals <std-proposals_at_[hidden] <mailto:std-proposals_at_[hidden]> > escreveu: undeclaring a variable is the same as relocating from a variable to nothingness (or to somewhere else).   A variable, which was relocated from, may also not be used any longer afterwards.     One detail may be the difference between position in the program (source code line within the block) and program flow.   int a = -1; for (int i = 0; i < 10; i++) { if (i == 5) a++; // can a be used here? if (i == 4) undecl a; if (i == 5) a++; // and here? }   -----Ursprüngliche Nachricht----- Von:wjf via Std-Proposals <std-proposals_at_[hidden] <mailto:std-proposals_at_[hidden]> > Gesendet:Mi 10.12.2025 02:23 Betreff:[std-proposals] [PXXXXR0] Add a New Keyword `undecl` Anlage:Add_New_Keyword_undecl.pdf An:std-proposals <std-proposals_at_[hidden] <mailto:std-proposals_at_[hidden]> >; CC:wjf <wjf_at_[hidden] <mailto:wjf_at_[hidden]> >; see attachment   wjf wjf_at_[hidden]   -- Std-Proposals mailing list Std-Proposals_at_[hidden] <mailto:Std-Proposals_at_[hidden]> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals -- Std-Proposals mailing list Std-Proposals_at_[hidden] <mailto:Std-Proposals_at_[hidden]> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals -- Std-Proposals mailing list Std-Proposals_at_[hidden] https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals