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* [Bug c++/114504] New: Non-structural type accepted as non-type template parameter type
@ 2024-03-27 23:06 ted at lyncon dot se
2024-03-27 23:14 ` [Bug c++/114504] " pinskia at gcc dot gnu.org
2024-03-27 23:23 ` [Bug c++/114504] Non-structural type accepted as non-type template parameter type for a template lambda function while in a concept pinskia at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: ted at lyncon dot se @ 2024-03-27 23:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114504
Bug ID: 114504
Summary: Non-structural type accepted as non-type template
parameter type
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ted at lyncon dot se
Target Milestone: ---
gcc accepts `NonStructuralType` as a non-type template parameter type below:
```
struct StructuralType1 {
constexpr StructuralType1(int A) : a(A) {}
int a;
};
struct NonStructuralType {
constexpr NonStructuralType(int A) : a(A) {}
private:
int a;
};
template <typename T>
concept is_structural = requires { []<T t> {}; };
static_assert(is_structural<StructuralType1>,
"BUG! StructuralType1 is not structural");
static_assert(!is_structural<NonStructuralType>,
"BUG! NontStructuralType is structural");
int main() {}
```
I was expecting `[]<T t>{}` to fail in the concept. The program compiles with
clang++, icx and MSVC.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/114504] Non-structural type accepted as non-type template parameter type
2024-03-27 23:06 [Bug c++/114504] New: Non-structural type accepted as non-type template parameter type ted at lyncon dot se
@ 2024-03-27 23:14 ` pinskia at gcc dot gnu.org
2024-03-27 23:23 ` [Bug c++/114504] Non-structural type accepted as non-type template parameter type for a template lambda function while in a concept pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-27 23:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114504
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2024-03-27
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So it looks like it is just an issue with the way requires is handled.
That is doing it outside of a requires rejects the code correctly:
```
...
template <typename T>
int f(void)
{
[]<T t> {};
return 0;
}
auto t = f<NonStructuralType>();
```
Is rejected correctly with:
```
<source>: In instantiation of 'int f() [with T = NonStructuralType]':
<source>:24:30: required from here
24 | auto t = f<NonStructuralType>();
| ~~~~~~~~~~~~~~~~~~~~^~
<source>:20:9: error: 'NonStructuralType' is not a valid type for a template
non-type parameter because it is not structural
20 | []<T t> {};
| ^~~~~~~~~~
<source>:10:9: note: 'NonStructuralType::a' is not public
10 | int a;
| ^
```
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/114504] Non-structural type accepted as non-type template parameter type for a template lambda function while in a concept
2024-03-27 23:06 [Bug c++/114504] New: Non-structural type accepted as non-type template parameter type ted at lyncon dot se
2024-03-27 23:14 ` [Bug c++/114504] " pinskia at gcc dot gnu.org
@ 2024-03-27 23:23 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-27 23:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114504
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |c++-lambda
Summary|Non-structural type |Non-structural type
|accepted as non-type |accepted as non-type
|template parameter type |template parameter type for
|while in concept |a template lambda function
| |while in a concept
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note GCC does the correct thing for:
```
...
template <typename T, T a> int f(void) { return 0; }
template <typename T>
concept is_structural = requires { f<T, T{1}>(); };
static_assert(!is_structural<NonStructuralType>);
```
So it is looking lambda related.
This also fails:
```
...
template <typename T>
void f(void)
{
[]<T t> {};
}
template <typename T>
concept is_structural = requires { f<T>(); };
static_assert(!is_structural<NonStructuralType>);
```
More proof that is lambda related.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-03-27 23:06 [Bug c++/114504] New: Non-structural type accepted as non-type template parameter type ted at lyncon dot se
2024-03-27 23:14 ` [Bug c++/114504] " pinskia at gcc dot gnu.org
2024-03-27 23:23 ` [Bug c++/114504] Non-structural type accepted as non-type template parameter type for a template lambda function while in a concept pinskia at gcc dot gnu.org
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