2016-11-15 Jonathan Wakely <jwakely@redhat.com>
+ * doc/xml/manual/intro.xml: Document LWG 2770 status. Remove entries
+ for 2742 and 2748.
+ * doc/html/*: Regenerate.
+ * include/std/utility (__tuple_size_cv_impl): New helper to safely
+ detect tuple_size<T>::value, as per LWG 2770.
+ (tuple_size<cv T>): Adjust partial specializations to derive from
+ __tuple_size_cv_impl.
+ * testsuite/20_util/tuple/cv_tuple_size.cc: Test SFINAE-friendliness.
+
* testsuite/libstdc++-prettyprinters/cxx17.cc: Adjust test for
variant<T&>.
<span class="emphasis"><em><code class="code">priority_queue</code> lacking comparator typedef
</em></span>
</span></dt><dd><p>Define the <code class="code">value_compare</code> typedef.
- </p></dd><dt><span class="term"><a class="link" href="../ext/lwg-defects.html#2742" target="_top">2742</a>:
- <span class="emphasis"><em>Inconsistent <code class="code">string</code> interface taking <code class="code">string_view</code>
+ </p></dd><dt><span class="term"><a class="link" href="../ext/lwg-defects.html#2770" target="_top">2770</a>:
+ <span class="emphasis"><em><code class="code">tuple_size<const T></code> specialization is not
+ SFINAE compatible and breaks decomposition declarations
</em></span>
- </span></dt><dd><p>Add the new constructor and additionally constrain it
- to avoid ambiguities with non-const <code class="code">charT*</code>.
- </p></dd><dt><span class="term"><a class="link" href="../ext/lwg-defects.html#2748" target="_top">2748</a>:
- <span class="emphasis"><em>swappable traits for optionals
- </em></span>
- </span></dt><dd><p>Disable the non-member <code class="code">swap</code> overload when
- the contained object is not swappable.
+ </span></dt><dd><p>Safely detect <code class="code">tuple_size<T>::value</code> and
+ only use it if valid.
</p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="license.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="status.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="setup.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">License </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 2. Setup</td></tr></table></div></body></html>
\ No newline at end of file
<listitem><para>Define the <code>value_compare</code> typedef.
</para></listitem></varlistentry>
- <varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2742">2742</link>:
- <emphasis>Inconsistent <code>string</code> interface taking <code>string_view</code>
+ <varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2770">2770</link>:
+ <emphasis><code>tuple_size<const T></code> specialization is not
+ SFINAE compatible and breaks decomposition declarations
</emphasis>
</term>
- <listitem><para>Add the new constructor and additionally constrain it
- to avoid ambiguities with non-const <code>charT*</code>.
- </para></listitem></varlistentry>
-
- <varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2748">2748</link>:
- <emphasis>swappable traits for optionals
- </emphasis>
- </term>
- <listitem><para>Disable the non-member <code>swap</code> overload when
- the contained object is not swappable.
+ <listitem><para>Safely detect <code>tuple_size<T>::value</code> and
+ only use it if valid.
</para></listitem></varlistentry>
</variablelist>
struct tuple_size;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
- // 2313. tuple_size should always derive from integral_constant<size_t, N>
+ // 2770. tuple_size<const T> specialization is not SFINAE compatible
+ template<typename _Tp, typename = void>
+ struct __tuple_size_cv_impl { };
+
template<typename _Tp>
- struct tuple_size<const _Tp>
+ struct __tuple_size_cv_impl<_Tp, __void_t<decltype(tuple_size<_Tp>::value)>>
: integral_constant<size_t, tuple_size<_Tp>::value> { };
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 2313. tuple_size should always derive from integral_constant<size_t, N>
+ template<typename _Tp>
+ struct tuple_size<const _Tp> : __tuple_size_cv_impl<_Tp> { };
+
template<typename _Tp>
- struct tuple_size<volatile _Tp>
- : integral_constant<size_t, tuple_size<_Tp>::value> { };
+ struct tuple_size<volatile _Tp> : __tuple_size_cv_impl<_Tp> { };
template<typename _Tp>
- struct tuple_size<const volatile _Tp>
- : integral_constant<size_t, tuple_size<_Tp>::value> { };
+ struct tuple_size<const volatile _Tp> : __tuple_size_cv_impl<_Tp> { };
/// Gives the type of the ith element of a given tuple type.
template<std::size_t __i, typename _Tp>
test01();
return 0;
}
+
+// LWG DR 2770. tuple_size<const T> specialization is not SFINAE compatible
+template<typename T, typename = void>
+struct has_value : std::false_type { };
+
+template<typename T>
+struct has_value<T, std::__void_t<decltype(T::value)>> : std::true_type { };
+
+static_assert( !has_value<std::tuple_size<int>>::value, "" );
+static_assert( !has_value<std::tuple_size<const int>>::value, "" );
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