http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51222
Bug #: 51222
Summary: [C++11][SFINAE] Unevaluated combined delete new
expression completely broken
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: daniel.krueg...@googlemail.com
CC: ja...@gcc.gnu.org
The following problem became obvious to me when I recently tried to provide a
both simpler and more general library emulation of is_constructible.
gcc 4.7 20111112 (experimental) in C++11 mode rejects the following code:
//---
template<class T>
struct add_rref {
typedef T&& type;
};
template<>
struct add_rref<void> {
typedef void type;
};
template<class T>
typename add_rref<T>::type declval();
template<class T, class U, class =
decltype(::delete ::new T(declval<U>()))
>
auto f(int) -> char;
template<class, class>
auto f(...) -> char(&)[2];
template<class T, class =
decltype(::delete ::new T())
>
auto g(int) -> char;
template<class>
auto g(...) -> char(&)[2];
struct C { };
struct A {
virtual ~A() = 0;
};
struct D1 {
D1() = delete;
};
struct D2 {
~D2() = delete;
};
static_assert(sizeof(g<void>(0)) == 2, "Ouch");
static_assert(sizeof(g<void()>(0)) == 2, "Ouch");
static_assert(sizeof(g<void() const>(0)) == 2, "Ouch");
static_assert(sizeof(g<A>(0)) == 2, "Ouch");
static_assert(sizeof(g<D1>(0)) == 2, "Ouch");
static_assert(sizeof(g<D2>(0)) == 2, "Ouch");
static_assert(sizeof(g<int&>(0)) == 2, "Ouch");
static_assert(sizeof(g<int&&>(0)) == 2, "Ouch");
static_assert(sizeof(g<void(&)()>(0)) == 2, "Ouch");
static_assert(sizeof(g<void(&&)()>(0)) == 2, "Ouch");
static_assert(sizeof(f<void, void>(0)) == 2, "Ouch");
static_assert(sizeof(f<void(), void()>(0)) == 2, "Ouch");
static_assert(sizeof(f<void() const, void() const>(0)) == 2, "Ouch");
static_assert(sizeof(f<int, void>(0)) == 2, "Ouch");
static_assert(sizeof(f<void, int>(0)) == 2, "Ouch");
static_assert(sizeof(f<C, void>(0)) == 2, "Ouch");
static_assert(sizeof(f<C, int>(0)) == 2, "Ouch");
static_assert(sizeof(f<int&, int&>(0)) == 2, "Ouch");
static_assert(sizeof(f<int&&, int&&>(0)) == 2, "Ouch");
static_assert(sizeof(f<void(&)(), void(&)()>(0)) == 2, "Ouch");
static_assert(sizeof(f<void(&&)(), void(&&)()>(0)) == 2, "Ouch");
//---
All static assertions fail, but they shouldn't. This is very unfortunate,
because above test expressions are extremely useful for emulating an effective
variable definition including destruction semantics.
The test code should be accepted.
