https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89881
Bug ID: 89881
Summary: Incorrect warning "-Wunneeded-internal-declaration"
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: lumosimann at gmail dot com
Target Milestone: ---
Suppose you have a concept implementation (pre-C++17). This might be something
like this:
#include <utility>
template <typename T, typename = void>
struct check_concept : std::false_type {};
template <typename T>
struct check_concept<T, std::enable_if_t<
std::is_same_v<decltype(f(std::declval<T>())), int>>> : std::true_type
{};
The type T fulfills the concept if there exists a function f that takes T and
returns int. There may be other functions required for the concept.
Now we are going to use the concept, maybe in a unittest.
namespace {
struct my_type {};
int f(my_type); // my_type implements the concept
static_assert(check_concept<my_type>::value, "");
}
This will warn about f being unneeded. Somehow it is, because it is not
actually emitted, but on the hand, f is needed because we want to ensure that f
fulfills the concept.
Is the warning correct or not?
See also https://godbolt.org/z/fROBm1
