Von: Zhihao Yuan via Std-Proposals <std-proposals@lists.isocpp.org>
Gesendet: Do 11.12.2025 23:59
Betreff: Re: [std-proposals] [PXXXXR0] Add a New Keyword `undecl`
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An: std-proposals@lists.isocpp.org;
CC: Zhihao Yuan <zy@miator.net>;
On Tuesday, December 9th, 2025 at 5:35 PM, Breno Guimarães via Std-Proposals <std-proposals@lists.isocpp.org> 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 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.
_______________________________________________
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@lists.isocpp.org> 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?
}
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Von: wjf via Std-Proposals <std-proposals@lists.isocpp.org>
Gesendet: Mi 10.12.2025 02:23
Betreff: [std-proposals] [PXXXXR0] Add a New Keyword `undecl`
Anlage: Add_New_Keyword_undecl.pdf
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CC: wjf <wjf@zenkee.cn>;
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