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* [Bug c++/105465] New: С++14 behaviour of inherited constructors broken
@ 2022-05-03 10:18 fchelnokov at gmail dot com
2022-05-03 17:07 ` [Bug c++/105465] " redi at gcc dot gnu.org
2022-05-03 17:08 ` redi at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: fchelnokov at gmail dot com @ 2022-05-03 10:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105465
Bug ID: 105465
Summary: С++14 behaviour of inherited constructors broken
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: fchelnokov at gmail dot com
Target Milestone: ---
In the following program struct B inherits A(Foo) constructor, which is called
from main:
#include <iostream>
struct Foo {
Foo() {}
Foo(const Foo&) { std::cout << "Foo(const Foo&)\n"; }
};
struct A {
A(Foo) {}
};
struct B : A {
using A::A;
};
int main() {
Foo f;
B b(f);
}
According to C++14 standard
(https://timsong-cpp.github.io/cppwp/n4140/class.inhctor#8) the compiler shall
produce
B::B(Foo f) : A(f) { }
so the call `B(f)` leads to 2 copies of Foo and the program shall print:
Foo(const Foo&)
Foo(const Foo&)
And indeed GCC 6.4 prints so. But starting from GCC 7 only one copy is made.
Demo: https://gcc.godbolt.org/z/sTqKzdj5v
Related discussion: https://stackoverflow.com/a/56241478/7325599
Is it a regression?
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/105465] С++14 behaviour of inherited constructors broken
2022-05-03 10:18 [Bug c++/105465] New: С++14 behaviour of inherited constructors broken fchelnokov at gmail dot com
@ 2022-05-03 17:07 ` redi at gcc dot gnu.org
2022-05-03 17:08 ` redi at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: redi at gcc dot gnu.org @ 2022-05-03 17:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105465
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
No it's not a regression, and it's not broken, it's correct.
https://wg21.link/P0136R1 changed the rules for C++17, resolving CWG1573,
CWG1645, CWG1715, CWG1736, CWG1903, CWG1941, CWG1959, and CWG1991 in the
process.
The old rule was inferior, nobody *wants* two copies of Foo there, that just
makes the program slower for no reason.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/105465] С++14 behaviour of inherited constructors broken
2022-05-03 10:18 [Bug c++/105465] New: С++14 behaviour of inherited constructors broken fchelnokov at gmail dot com
2022-05-03 17:07 ` [Bug c++/105465] " redi at gcc dot gnu.org
@ 2022-05-03 17:08 ` redi at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: redi at gcc dot gnu.org @ 2022-05-03 17:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105465
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And this was already explained in the stackoverflow answer.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-05-03 10:18 [Bug c++/105465] New: С++14 behaviour of inherited constructors broken fchelnokov at gmail dot com
2022-05-03 17:07 ` [Bug c++/105465] " redi at gcc dot gnu.org
2022-05-03 17:08 ` redi at gcc dot gnu.org
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