https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116739
Bug ID: 116739
Summary: template parameter confusion results in parameter
packs not expanded with '...'
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ted at lyncon dot se
Target Milestone: ---
The following results in `error: parameter packs not expanded with '...'` in
all versions of g++ that I could test @ godbolt.com.
Changing the member function template to use a different name than `type` for
the parameter pack makes the program compile.
```
#include <iostream>
#include <optional>
#include <tuple>
#include <type_traits>
template <class... types>
struct type_or_tuple {
using tup = std::tuple<types...>;
using type = std::conditional_t<sizeof...(types) == 1,
std::tuple_element_t<0, tup>, tup>;
};
template <class... types>
using type_or_tuple_t = typename type_or_tuple<types...>::type;
template <class... types>
class myclass {
using payload_type = type_or_tuple_t<types...>;
template <class... type>
// error: parameter packs not expanded with '...':
std::optional<payload_type> try_push(type&&... data) {
payload_type t;
std::optional<decltype(t)> o;
return o;
}
};
int main() { [[maybe_unused]] myclass<unsigned> c; }
```
