https://bugs.llvm.org/show_bug.cgi?id=45158
Bug ID: 45158
Summary: __is_constructible intrinsic does not SFINAE on
default member initializers
Product: clang
Version: 9.0
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: alisda...@me.com
CC: blitzrak...@gmail.com, dgre...@apple.com,
erik.pilking...@gmail.com, llvm-bugs@lists.llvm.org,
richard-l...@metafoo.co.uk
The various standard type traits querying whether a type is constructible are
implemented (in both libc++ and libstdc++) as ultimately delegating to an
intrinsic such as __is_constructible. This trait fails to account for default
member initializers, which produce a hard error rather than returning a
true/false answer when evaluating the intrinsic, and hence the trait.
Example:
#include <type_traits>
template <class T>
struct Wrap {
Wrap() = default;
T data{}; // default member initializer
};
struct NoDefault {
NoDefault(NoDefault const&) {} // non-trivial, not an aggregate
};
int main() {
using namespace std;
static_assert(!is_default_constructible<Wrap<NoDefault>>::value, "bad");
}
Godbolt link for quick experimentation: https://godbolt.org/z/-D9mpA
This fails with both libc++ and libstdc++, for all dialects of C++11 and later,
for all online compilers up to and including trunk.
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