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* [Bug libstdc++/56283] New: std::result_of does not gracefully SFINAE (not define ::type)
@ 2013-02-11 4:10 potswa at mac dot com
2013-02-11 4:58 ` [Bug libstdc++/56283] " potswa at mac dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: potswa at mac dot com @ 2013-02-11 4:10 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56283
Bug #: 56283
Summary: std::result_of does not gracefully SFINAE (not define
::type)
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: potswa@mac.com
>From the spec of std::result_of,
If the expression INVOKE(declval<Fn>(), declval<ArgTypes>()...) is well formed
when treated as an unevaluated operand (Clause 5), the member typedef type
shall name the type decltype(INVOKE(declval<Fn>(), declval<ArgTypes>()...));
otherwise, there shall be no member type.
If the given INVOKE expression is invalid, ::type should not exist. But an
attempt to use it this way to detect a valid call fails.
Below is a short demo program. A non-overloaded function name and a functor
type with an overloaded call operator are passed to result_of through a type
traits style SFINAE wrapper. None of the cases work. In 2 of the 3 cases the
failure fires the static assertion, but not for the multiple overload issue.
#include <type_traits>
template< typename fn, typename = void >
struct is_invokable : std::false_type {};
template< typename fn >
struct is_invokable< fn, typename std::conditional< true, void, typename
std::result_of< fn >::type >::type >
: std::true_type {};
void f( int );
static_assert( ! is_invokable< decltype( f ) &( char const * ) >(), "can
convert c-string to int" );
struct s {
void operator() ( int ) {}
void operator() ( float ) {}
};
static_assert( ! is_invokable< s( double ) >(), "resolved ambiguous conversion"
);
static_assert( ! is_invokable< s( char * ) >(), "converted pointer to number"
);
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/56283] std::result_of does not gracefully SFINAE (not define ::type) 2013-02-11 4:10 [Bug libstdc++/56283] New: std::result_of does not gracefully SFINAE (not define ::type) potswa at mac dot com @ 2013-02-11 4:58 ` potswa at mac dot com 2013-02-11 10:06 ` redi at gcc dot gnu.org 2013-02-11 10:07 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: potswa at mac dot com @ 2013-02-11 4:58 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56283 --- Comment #1 from David Krauss <potswa at mac dot com> 2013-02-11 04:57:46 UTC --- Note, defining the trait with the expression declval<Fn>()(declval<ArgTypes>()...) does work. Clang 3.1/libc++ behaves the same way. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/56283] std::result_of does not gracefully SFINAE (not define ::type) 2013-02-11 4:10 [Bug libstdc++/56283] New: std::result_of does not gracefully SFINAE (not define ::type) potswa at mac dot com 2013-02-11 4:58 ` [Bug libstdc++/56283] " potswa at mac dot com @ 2013-02-11 10:06 ` redi at gcc dot gnu.org 2013-02-11 10:07 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: redi at gcc dot gnu.org @ 2013-02-11 10:06 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56283 --- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-11 10:05:58 UTC --- You're looking at a post-C++11 draft, not at the standard. The change was made by http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3462.html and GCC 4.8 already implements the new behaviour, but 4.7 isn't going to. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/56283] std::result_of does not gracefully SFINAE (not define ::type) 2013-02-11 4:10 [Bug libstdc++/56283] New: std::result_of does not gracefully SFINAE (not define ::type) potswa at mac dot com 2013-02-11 4:58 ` [Bug libstdc++/56283] " potswa at mac dot com 2013-02-11 10:06 ` redi at gcc dot gnu.org @ 2013-02-11 10:07 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: redi at gcc dot gnu.org @ 2013-02-11 10:07 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56283 Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution| |WORKSFORME Target Milestone|--- |4.8.0 --- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-11 10:07:06 UTC --- . ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2013-02-11 10:07 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2013-02-11 4:10 [Bug libstdc++/56283] New: std::result_of does not gracefully SFINAE (not define ::type) potswa at mac dot com 2013-02-11 4:58 ` [Bug libstdc++/56283] " potswa at mac dot com 2013-02-11 10:06 ` redi at gcc dot gnu.org 2013-02-11 10:07 ` redi at gcc dot gnu.org
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