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Re: [C++ Patch/RFC] PR 56450


Hi again,

On 04/27/2013 02:56 AM, Jason Merrill wrote:
Why should id_expression_or_member_access_p be false? "declval<T>().dummy" is a class member access (5.2.5) regardless of what kind of member dummy is.
today I have been able to spend some more time on the issue, and I think the attached further reduced testcase summarizes rather well what I figured out.

Assuming as obvious that we don't want to crash on it, the interesting issue is whether we want the static_asserts to both fail or succeed: in practice, a rather recent ICC I have at hand fails both; a rather recent clang++ passes both (consistently with the expectation of Bug submitter). In fact, as I'm reading now 7.1.6.2/4, since we are dealing with a class member access in any case, it may well be possible that *ICC* is right. And then a tiny patch like the attached works for me to obtain the same behavior for GCC (passes testing etc; it's the first "stupid" thing I tried days ago ;)

FWIW, the attached testcase also explains pretty well why my earlier hack appeared to work, in the sense of recent clang++: we ended up calling cp_build_reference_type on the type.

Overall, I think the situation is rather clear by now. What do you think?

Thanks!
Paolo.

////////////////////////
template<typename T>
T&& declval();

template<typename, typename>
struct is_same
{ static constexpr bool value = false; };

template<typename T>
struct is_same<T, T>
{ static constexpr bool value = true; };

struct A
{
  static const int dummy = 0;
};

static_assert(!is_same<decltype(declval<A>().dummy), const int>::value, "");
static_assert(is_same<decltype(declval<A>().dummy), const int&>::value, "");

Attachment: p
Description: Text document


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