https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95269
Bug ID: 95269
Summary: Lambda is allowed to capture any constexpr variable
without specifying any captures
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dragondreamer at live dot com
Target Milestone: ---
G++ (at least these versions: 8.2.1, 9.2.1, 10.1.0, trunk) successfully
compiles the following code:
// ===================================
template<typename Lambda>
constexpr void test(Lambda lambda)
{
constexpr auto result = lambda();
static_assert(result.value == 1);
}
struct teststruct
{
int value = 0;
};
constexpr auto get_value()
{
teststruct result{};
result.value = 1;
return result;
}
int main()
{
constexpr auto value = get_value();
//Here's a lambda without any captures
auto options_lambda = []() { return value; };
test(options_lambda);
}
// ===================================
This code instead should produce an error when trying to create a lambda which
uses "value" without capturing it. This is the exact behavior of Clang and
MSVC, which both produce an error message.
As far as I understand, the following rule must be applied here:
"If a lambda expression (or an instantiation of a generic lambda's function
call operator) ODR-uses this or any variable with automatic storage duration,
it must be captured by the lambda expression."
