https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64352
Bug ID: 64352
Summary: [5.0 regression] No SFINAE with deleted function
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: lucdanton at free dot fr
Created attachment 34300
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34300&action=edit
Minimal testcase
Using:
g++-trunk (GCC) 5.0.0 20141218 (experimental)
Testcase:
template<bool B> struct bool_type
{ static constexpr bool value = B; };
using true_type = bool_type<true>;
using false_type = bool_type<false>;
template<typename T> T&& declval();
template<typename...> struct void_ { using type = void; };
template<typename... I> using void_t = typename void_<I...>::type;
template<typename _Tp, typename = void>
struct _Has_addressof_free: false_type { };
template<typename _Tp>
struct _Has_addressof_free
<_Tp, void_t<decltype( operator&(declval<const _Tp&>()) )>>
: true_type { };
struct foo {};
void operator&(foo) = delete;
int main()
{
static_assert( !_Has_addressof_free<int>::value, "" );
// error: use of deleted function 'void operator&(foo)'
static_assert( _Has_addressof_free<foo>::value, "" );
}
This produces the following:
$ g++-trunk -std=c++11 main.cpp
main.cpp: In function 'int main()':
main.cpp:17:33: error: use of deleted function 'void operator&(foo)'
<_Tp, void_t<decltype( operator&(declval<const _Tp&>()) )>>
^
main.cpp:21:6: note: declared here
void operator&(foo) = delete;
^
main.cpp:27:5: error: static assertion failed:
static_assert( _Has_addressof_free<foo>::value, "" );
^
I'm not entirely sure this is a regression, e.g. libstdc++'s
testsuite/experimental/optional/observers/2.cc is very similar
but passes. I'm working on experimental/optional however and
I ended up tripping over this, and I didn't touch the
_Has_addressof_* stuff. It is copied (almost) verbatim here,
but not the declval/true_type/false_type/[__]void[_t] bits,
in case that's of any help.
Changing the deleted definition with e.g. a dummy definition
('{}') makes the program compiles as expected.
