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* [Bug c++/94922] New: Functional cast from base class to derived class incorrectly accepted with -std=c++2a
@ 2020-05-02 12:53 ppalka at gcc dot gnu.org
2020-05-02 12:57 ` [Bug c++/94922] " ppalka at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: ppalka at gcc dot gnu.org @ 2020-05-02 12:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94922
Bug ID: 94922
Summary: Functional cast from base class to derived class
incorrectly accepted with -std=c++2a
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ppalka at gcc dot gnu.org
Target Milestone: ---
$ cat testcase.C
struct base {};
struct derived : base {};
template <typename T, typename R, typename = decltype(T(R()))>
void foo();
void
bar()
{
foo<derived, base>();
}
$ g++-10 -std=c++2a testcase.C
$ g++-10 -std=c++17 testcase.C
testcase.C: In function ‘void bar()’:
testcase.C:10:22: error: no matching function for call to ‘foo<derived,
base>()’
13 | foo<derived, base>();
| ^
...
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/94922] Functional cast from base class to derived class incorrectly accepted with -std=c++2a
2020-05-02 12:53 [Bug c++/94922] New: Functional cast from base class to derived class incorrectly accepted with -std=c++2a ppalka at gcc dot gnu.org
@ 2020-05-02 12:57 ` ppalka at gcc dot gnu.org
2020-05-02 13:00 ` ppalka at gcc dot gnu.org
2020-05-03 4:31 ` ppalka at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: ppalka at gcc dot gnu.org @ 2020-05-02 12:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94922
--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
The above appears to be a 10/11 regression, but note that all versions of GCC
>= 4.7 also incorrectly accept the following testcase:
struct base {};
struct derived : base {};
template <typename = decltype(derived(base()))>
void foo();
void
bar()
{
foo();
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/94922] Functional cast from base class to derived class incorrectly accepted with -std=c++2a
2020-05-02 12:53 [Bug c++/94922] New: Functional cast from base class to derived class incorrectly accepted with -std=c++2a ppalka at gcc dot gnu.org
2020-05-02 12:57 ` [Bug c++/94922] " ppalka at gcc dot gnu.org
@ 2020-05-02 13:00 ` ppalka at gcc dot gnu.org
2020-05-03 4:31 ` ppalka at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: ppalka at gcc dot gnu.org @ 2020-05-02 13:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94922
--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Another testcase that exhibits the 10/11 regression:
struct base {};
struct derived : base {};
void
foo()
{
derived a = derived(base());
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/94922] Functional cast from base class to derived class incorrectly accepted with -std=c++2a
2020-05-02 12:53 [Bug c++/94922] New: Functional cast from base class to derived class incorrectly accepted with -std=c++2a ppalka at gcc dot gnu.org
2020-05-02 12:57 ` [Bug c++/94922] " ppalka at gcc dot gnu.org
2020-05-02 13:00 ` ppalka at gcc dot gnu.org
@ 2020-05-03 4:31 ` ppalka at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: ppalka at gcc dot gnu.org @ 2020-05-03 4:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94922
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Upon closer investigation I think we're correct to accept these testcases. As
I understand it the construction 'Derived(Base())' is valid in C++20 as a
direct consequence of C++17's aggregate init of classes with base classes
(P0017R1) in conjunction with C++20's parenthesized init of aggregates
(P0960R3).
Thus closing this bug as invalid, sorry for the noise.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-05-03 4:31 UTC | newest]
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2020-05-02 12:53 [Bug c++/94922] New: Functional cast from base class to derived class incorrectly accepted with -std=c++2a ppalka at gcc dot gnu.org
2020-05-02 12:57 ` [Bug c++/94922] " ppalka at gcc dot gnu.org
2020-05-02 13:00 ` ppalka at gcc dot gnu.org
2020-05-03 4:31 ` ppalka at gcc dot gnu.org
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