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* [Bug c++/95269] New: Lambda is allowed to capture any constexpr variable without specifying any captures
@ 2020-05-22 8:30 dragondreamer at live dot com
2021-08-28 22:34 ` [Bug c++/95269] " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: dragondreamer at live dot com @ 2020-05-22 8:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95269
Bug ID: 95269
Summary: Lambda is allowed to capture any constexpr variable
without specifying any captures
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dragondreamer at live dot com
Target Milestone: ---
G++ (at least these versions: 8.2.1, 9.2.1, 10.1.0, trunk) successfully
compiles the following code:
// ===================================
template<typename Lambda>
constexpr void test(Lambda lambda)
{
constexpr auto result = lambda();
static_assert(result.value == 1);
}
struct teststruct
{
int value = 0;
};
constexpr auto get_value()
{
teststruct result{};
result.value = 1;
return result;
}
int main()
{
constexpr auto value = get_value();
//Here's a lambda without any captures
auto options_lambda = []() { return value; };
test(options_lambda);
}
// ===================================
This code instead should produce an error when trying to create a lambda which
uses "value" without capturing it. This is the exact behavior of Clang and
MSVC, which both produce an error message.
As far as I understand, the following rule must be applied here:
"If a lambda expression (or an instantiation of a generic lambda's function
call operator) ODR-uses this or any variable with automatic storage duration,
it must be captured by the lambda expression."
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/95269] Lambda is allowed to capture any constexpr variable without specifying any captures
2020-05-22 8:30 [Bug c++/95269] New: Lambda is allowed to capture any constexpr variable without specifying any captures dragondreamer at live dot com
@ 2021-08-28 22:34 ` pinskia at gcc dot gnu.org
2021-08-28 22:42 ` pinskia at gcc dot gnu.org
2022-02-03 5:00 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-28 22:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95269
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC and ICC accept this while clang and MSVC reject this.
Without constexpr for value, GCC and ICC do reject this.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/95269] Lambda is allowed to capture any constexpr variable without specifying any captures
2020-05-22 8:30 [Bug c++/95269] New: Lambda is allowed to capture any constexpr variable without specifying any captures dragondreamer at live dot com
2021-08-28 22:34 ` [Bug c++/95269] " pinskia at gcc dot gnu.org
@ 2021-08-28 22:42 ` pinskia at gcc dot gnu.org
2022-02-03 5:00 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-28 22:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95269
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=93842
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So I don't think this is an ODR use of the constexpr.
If I change the lambda be this, GCC rejects it correctly.
auto options_lambda = []() ->auto& { return value; };
So it all depends on what the return type of the original lambda should be
really.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/95269] Lambda is allowed to capture any constexpr variable without specifying any captures
2020-05-22 8:30 [Bug c++/95269] New: Lambda is allowed to capture any constexpr variable without specifying any captures dragondreamer at live dot com
2021-08-28 22:34 ` [Bug c++/95269] " pinskia at gcc dot gnu.org
2021-08-28 22:42 ` pinskia at gcc dot gnu.org
@ 2022-02-03 5:00 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-02-03 5:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95269
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |DUPLICATE
Status|UNCONFIRMED |RESOLVED
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 88164.
*** This bug has been marked as a duplicate of bug 88164 ***
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-02-03 5:00 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2020-05-22 8:30 [Bug c++/95269] New: Lambda is allowed to capture any constexpr variable without specifying any captures dragondreamer at live dot com
2021-08-28 22:34 ` [Bug c++/95269] " pinskia at gcc dot gnu.org
2021-08-28 22:42 ` pinskia at gcc dot gnu.org
2022-02-03 5:00 ` pinskia at gcc dot gnu.org
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