https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96999
Bug ID: 96999
Summary: regression: std::variant requires default constructor
with gcc 8-9, gcc 7.x and 10.x works
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dushistov at mail dot ru
Target Milestone: ---
For code bellow, gcc 9.3 from Ubuntu reports error:
```
In file included from /usr/include/c++/9/variant:36,
from test.cpp:1:
...
/usr/include/c++/9/type_traits:931:47: error: ‘Foo::Foo()’ is private within
this context
931 | : public integral_constant<bool, noexcept(_Tp())>
| ^~~~~
test.cpp:10:3: note: declared private here
10 | Foo() noexcept {}
| ^~~
```
gcc 8.x also reports error. gcc 7.x and 10.x works just fine:
```
#include <variant>
#include <string>
struct Foo {
public:
explicit Foo(int) noexcept {}
Foo(Foo &&) noexcept = default;
Foo &operator=(Foo &&) = default;
private:
Foo() noexcept {}
};
struct Boo {
public:
explicit Boo(int) noexcept {}
Boo(Boo &&) noexcept = default;
Boo &operator=(Boo &&) = default;
private:
Boo() noexcept {}
};
template<bool X>
std::variant<Foo, Boo> g(int v, int x) {
return v == 0 ? std::variant<Foo, Boo>{Foo{x}} :
std::variant<Foo, Boo>{Boo{x}};
}
int main()
{
std::variant<std::variant<Foo, Boo>, std::string> err{std::string("aaa")};
}
```
