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* [Bug c++/110774] New: Ambiguous partial ordering with non-dependent function parameter type
@ 2023-07-22 1:03 bbi5291 at gmail dot com
2023-07-22 1:04 ` [Bug c++/110774] " pinskia at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: bbi5291 at gmail dot com @ 2023-07-22 1:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110774
Bug ID: 110774
Summary: Ambiguous partial ordering with non-dependent function
parameter type
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: bbi5291 at gmail dot com
Target Milestone: ---
With `g++ -std=c++2b`, the following is rejected:
---
template<typename T>
struct A { typedef char* type; };
template<typename T> char* f1(T, char*); // #1
template<typename T> long* f1(T*, typename A<T>::type*); // #2
long* p1 = f1(p1, 0); // #3
---
The error message is:
---
<source>:7:14: error: call of overloaded 'f1(long int*&, int)' is ambiguous
7 | long* p1 = f1(p1, 0); // #3
| ~~^~~~~~~
<source>:4:28: note: candidate: 'char* f1(T, char*) [with T = long int*]'
4 | template<typename T> char* f1(T, char*); // #1
| ^~
<source>:5:28: note: candidate: 'long int* f1(T*, typename A<T>::type*) [with T
= long int; typename A<T>::type = char*]'
5 | template<typename T> long* f1(T*, typename A<T>::type*); // #2
| ^~
---
This code is very similar to the code from Core issue 455, but one of the
function parameters has been changed from containing `T` in a non-deduced
context to not containing `T` at all. Since the code from core issue 455 is
supposed to be valid (#2 being chosen) I cannot see any reason why this example
would not also be valid. A non-dependent parameter type should be treated the
same as a parameter type containing the template parameter in a non-deduced
context: in either case, it cannot be used for deduction.
Clang and MSVC also reject this code, but I cannot find any reason why. Is it
possible that all 3 compilers have a bug?
Reflector thread: https://lists.isocpp.org/core/2023/07/14533.php
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type
2023-07-22 1:03 [Bug c++/110774] New: Ambiguous partial ordering with non-dependent function parameter type bbi5291 at gmail dot com
@ 2023-07-22 1:04 ` pinskia at gcc dot gnu.org
2023-07-22 1:07 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-07-22 1:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110774
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The literal 0 is the issue ...
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type
2023-07-22 1:03 [Bug c++/110774] New: Ambiguous partial ordering with non-dependent function parameter type bbi5291 at gmail dot com
2023-07-22 1:04 ` [Bug c++/110774] " pinskia at gcc dot gnu.org
@ 2023-07-22 1:07 ` pinskia at gcc dot gnu.org
2023-07-22 1:12 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-07-22 1:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110774
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually 0 vs nullptr is the same:
```
template<typename T>
struct A { typedef char* type; };
template<typename T> char* f1(T, char*); // #1
template<typename T> long* f1(T*, typename A<T>::type*); // #2
long* p1 = f1(p1, nullptr); // #3
```
That is the above also gets ambiguous.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type
2023-07-22 1:03 [Bug c++/110774] New: Ambiguous partial ordering with non-dependent function parameter type bbi5291 at gmail dot com
2023-07-22 1:04 ` [Bug c++/110774] " pinskia at gcc dot gnu.org
2023-07-22 1:07 ` pinskia at gcc dot gnu.org
@ 2023-07-22 1:12 ` pinskia at gcc dot gnu.org
2023-07-22 1:15 ` [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type and nullptr pinskia at gcc dot gnu.org
2023-07-22 1:17 ` bbi5291 at gmail dot com
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-07-22 1:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110774
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Take:
```
template<typename T>
struct A { typedef char* type; };
template<typename T> char* f1(T, char*); // #1
template<typename T> long* f1(T*, typename A<T>::type*); // #2
char *t;
char **t1;
long* p0;
long *p1 = f1(p0, t1); // choses #2
char* p2 = f1(p0, t); // choses #1
```
GCC, MSVC, and clang all compile the above.
So is it only an issue with nullptr where it could chose either?
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type and nullptr
2023-07-22 1:03 [Bug c++/110774] New: Ambiguous partial ordering with non-dependent function parameter type bbi5291 at gmail dot com
` (2 preceding siblings ...)
2023-07-22 1:12 ` pinskia at gcc dot gnu.org
@ 2023-07-22 1:15 ` pinskia at gcc dot gnu.org
2023-07-22 1:17 ` bbi5291 at gmail dot com
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-07-22 1:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110774
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
But these function declarations are not partial specializations as far as I
know.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type and nullptr
2023-07-22 1:03 [Bug c++/110774] New: Ambiguous partial ordering with non-dependent function parameter type bbi5291 at gmail dot com
` (3 preceding siblings ...)
2023-07-22 1:15 ` [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type and nullptr pinskia at gcc dot gnu.org
@ 2023-07-22 1:17 ` bbi5291 at gmail dot com
4 siblings, 0 replies; 6+ messages in thread
From: bbi5291 at gmail dot com @ 2023-07-22 1:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110774
--- Comment #5 from Brian Bi <bbi5291 at gmail dot com> ---
Partial ordering is different from partial specialization. Partial ordering
selects a best viable function in certain cases where two viable functions are
both instantiated from templates.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-07-22 1:17 UTC | newest]
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2023-07-22 1:03 [Bug c++/110774] New: Ambiguous partial ordering with non-dependent function parameter type bbi5291 at gmail dot com
2023-07-22 1:04 ` [Bug c++/110774] " pinskia at gcc dot gnu.org
2023-07-22 1:07 ` pinskia at gcc dot gnu.org
2023-07-22 1:12 ` pinskia at gcc dot gnu.org
2023-07-22 1:15 ` [Bug c++/110774] Ambiguous partial ordering with non-dependent function parameter type and nullptr pinskia at gcc dot gnu.org
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