[libc++] Overhaul std::quoted; fix its relationship to character traits.

[• Quuxplusone]

Summary

https://en.cppreference.com/w/cpp/io/manip/quoted

Move __quoted_output_proxy into the one file that uses it. (This was the top of the rabbit hole... :))

A const char* has no associated traits class, so std::quoted("literal") should be printable into any basic_ostream regardless of traits.

Use hidden-friend operator<< and operator>>, since we're permitted to. (The exact signature is unspecified because the class itself is unspecified.)

We shouldn't support std::quoted("literal") in C++03 or C++11 mode. (We do need std::__quoted(s) and std::__quoted(cs) in C++11 mode, because they're used by std::__fs::filesystem::path.)

Use _LIBCPP_HIDDEN and _LIBCPP_HIDE_FROM_ABI consistently.

[• Quuxplusone]

Poke CI after adding the parent revision.

[philnik]

If you have multiple commits for this mess it would be nice to have multiple PRs.

libcxx/include/__filesystem/path.h

971

libcxx/include/iomanip

521

525

579

[• Quuxplusone]

If you have multiple commits for this mess it would be nice to have multiple PRs.

Sadly I don't. Most of the changes end up being interrelated anyway (e.g. operator<< can be a hidden friend, but also we change its signature at the same time; __quoted_output_proxy moves, but also goes under an #if at the same time...). I could probably disentangle the original "move __quoted_output_proxy to <iomanip>" change into its own commit, but that might be about all.

libcxx/include/__filesystem/path.h

971

Here I'm naturally inclined to match line 963, but I could go either way.

libcxx/include/iomanip

525

Yup, looks like (; is libc++ style. Will switch.

579

Here I'll stick with Standardese style (which is also, generally speaking, libc++ style): int *p, int& r.

596–597

I've added _LIBCPP_HIDE_FROM_ABI to this ctor. That's correct, right? @ldionne

[ldionne]

Is there any way you can land the style changes (whitespace and other consistency stuff) as a separate NFC commit, and re-upload this one so we can take a look?

libcxx/include/iomanip

596–597

Yes, that looks correct to me.

libcxx/test/std/input.output/iostream.format/quoted.manip/quoted_traits.compile.pass.cpp

10

We already have libcxx/test/std/input.output/iostream.format/quoted.manip/quoted.pass.cpp. Can you please add a comment explaining what this is actually testing, since it's obviously different from libcxx/test/std/input.output/iostream.format/quoted.manip/quoted.pass.cpp.

146

I think that's what you mean -- same above.

[• Quuxplusone]

Push a lot of the non-functional diffs (and the ADL-proofing) to main in small separate commits, and then rebase.

[• Quuxplusone]

Undo a few diffs I'm not married to.

[ldionne]

Can you add a release note for the removal of quoted("literal") before C++14?

libcxx/include/__filesystem/path.h

_LIBCPP_INLINE_VISIBILITY friend
     __os << _VSTD::__quoted(__p.string<_CharT, _Traits>());
     return __os;
   }
 
   template <class _CharT, class _Traits>
   _LIBCPP_INLINE_VISIBILITY friend basic_istream<_CharT, _Traits>&
   operator>>(basic_istream<_CharT, _Traits>& __is, path& __p) {
     basic_string<_CharT, _Traits> __tmp;
-    __is >> __quoted(__tmp);
+    __is >> _VSTD::__quoted(__tmp);
     __p = __tmp;
     return __is;
   }
 #endif // !_LIBCPP_HAS_NO_LOCALIZATION
 
   friend _LIBCPP_INLINE_VISIBILITY bool operator==(const path& __lhs, const path& __rhs) noexcept {
     return __lhs.__compare(__rhs.__pn_) == 0;
   }

libcxx/include/__string

 template<class _Ptr>
 inline _LIBCPP_INLINE_VISIBILITY
 size_t __do_string_hash(_Ptr __p, _Ptr __e)
 {
     typedef typename iterator_traits<_Ptr>::value_type value_type;
     return __murmur2_or_cityhash<size_t>()(__p, (__e-__p)*sizeof(value_type));
 }
 
-template <class _CharT, class _Iter, class _Traits=char_traits<_CharT> >
-struct __quoted_output_proxy
-{
-    _Iter  __first;
-    _Iter  __last;
-    _CharT  __delim;
-    _CharT  __escape;
-
-    explicit __quoted_output_proxy(_Iter __f, _Iter __l, _CharT __d, _CharT __e)
-        : __first(__f), __last(__l), __delim(__d), __escape(__e) {}
-    //  This would be a nice place for a string_ref
-};
-
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP___STRING

libcxx/include/iomanip

 template <class _CharT>
 inline _LIBCPP_INLINE_VISIBILITY
 __iom_t10<_CharT>
 put_time(const tm* __tm, const _CharT* __fmt)
 {
     return __iom_t10<_CharT>(__tm, __fmt);
 }
 
-template <class _CharT, class _Traits, class _ForwardIterator>
-basic_ostream<_CharT, _Traits> &
-__quoted_output ( basic_ostream<_CharT, _Traits> &__os,
-        _ForwardIterator __first, _ForwardIterator __last, _CharT __delim, _CharT __escape )
+#if _LIBCPP_STD_VER >= 11
+
+template <class _CharT, class _Traits>
+_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
+__quoted_output(basic_ostream<_CharT, _Traits>& __os,
+                const _CharT *__first, const _CharT *__last, _CharT __delim, _CharT __escape)
 {
     basic_string<_CharT, _Traits> __str;
     __str.push_back(__delim);
-    for ( ; __first != __last; ++ __first )
+    for ( ; __first != __last; ++__first)
     {
-        if (_Traits::eq (*__first, __escape) || _Traits::eq (*__first, __delim))
+        if (_Traits::eq(*__first, __escape) || _Traits::eq(*__first, __delim))
             __str.push_back(__escape);
         __str.push_back(*__first);
     }
     __str.push_back(__delim);
-    return _VSTD::__put_character_sequence(__os, __str.data(), __str.size());
+    return std::__put_character_sequence(__os, __str.data(), __str.size());
 }
 
 template <class _CharT, class _Traits, class _String>
-basic_istream<_CharT, _Traits> &
-__quoted_input ( basic_istream<_CharT, _Traits> &__is, _String & __string, _CharT __delim, _CharT __escape )
+_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
+__quoted_input(basic_istream<_CharT, _Traits>& __is, _String& __string, _CharT __delim, _CharT __escape)
 {
-    __string.clear ();
+    __string.clear();
     _CharT __c;
     __is >> __c;
-    if ( __is.fail ())
+    if (__is.fail())
         return __is;
 
-    if (!_Traits::eq (__c, __delim))    // no delimiter, read the whole string
+    if (!_Traits::eq(__c, __delim))    // no delimiter, read the whole string
     {
-        __is.unget ();
+        __is.unget();
         __is >> __string;
         return __is;
     }
 
-    __save_flags<_CharT, _Traits> sf(__is);
-    noskipws (__is);
-    while (true)
-        {
+    __save_flags<_CharT, _Traits> __sf(__is);
+    std::noskipws(__is);
+    while (true) {
         __is >> __c;
-        if ( __is.fail ())
+        if (__is.fail())
             break;
-        if (_Traits::eq (__c, __escape))
-        {
+        if (_Traits::eq(__c, __delim))
+            break;
+        if (_Traits::eq(__c, __escape)) {
             __is >> __c;
-            if ( __is.fail ())
+            if (__is.fail())
                 break;
         }
-        else if (_Traits::eq (__c, __delim))
-            break;
-        __string.push_back ( __c );
-        }
+        __string.push_back(__c);
     return __is;
 }
 
-
-template <class _CharT, class _Traits, class _Iter>
-basic_ostream<_CharT, _Traits>& operator<<(
-         basic_ostream<_CharT, _Traits>& __os,
-         const __quoted_output_proxy<_CharT, _Iter, _Traits> & __proxy)
+template <class _CharT, class _Traits>
+struct _LIBCPP_HIDDEN __quoted_output_proxy
 {
-    return __quoted_output(__os, __proxy.__first, __proxy.__last, __proxy.__delim, __proxy.__escape);
+    const _CharT *__first_;
+    const _CharT *__last_;
+    _CharT __delim_;
+    _CharT __escape_;
+
+    _LIBCPP_HIDE_FROM_ABI
+    explicit __quoted_output_proxy(const _CharT *__f, const _CharT *__l, _CharT __d, _CharT __e)
+        : __first_(__f), __last_(__l), __delim_(__d), __escape_(__e) {}
+
+    template<class _T2, __enable_if_t<_IsSame<_Traits, void>::value || _IsSame<_Traits, _T2>::value>* = nullptr>
+    friend _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _T2>&
+    operator<<(basic_ostream<_CharT, _T2>& __os, const __quoted_output_proxy& __p) {
+        return std::__quoted_output(__os, __p.__first_, __p.__last_, __p.__delim_, __p.__escape_);
     }
+};
 
 template <class _CharT, class _Traits, class _Allocator>
-struct __quoted_proxy
+struct _LIBCPP_HIDDEN __quoted_proxy
 {
-    basic_string<_CharT, _Traits, _Allocator> &__string;
-    _CharT  __delim;
-    _CharT  __escape;
+    basic_string<_CharT, _Traits, _Allocator>& __string_;
+    _CharT __delim_;
+    _CharT __escape_;
 
-    explicit __quoted_proxy(basic_string<_CharT, _Traits, _Allocator> &__s, _CharT __d, _CharT __e)
-        : __string(__s), __delim(__d), __escape(__e) {}
-};
-
-template <class _CharT, class _Traits, class _Allocator>
-_LIBCPP_INLINE_VISIBILITY
-basic_ostream<_CharT, _Traits>& operator<<(
-        basic_ostream<_CharT, _Traits>& __os,
-        const __quoted_proxy<_CharT, _Traits, _Allocator> & __proxy)
-{
-    return __quoted_output (__os, __proxy.__string.cbegin (), __proxy.__string.cend (), __proxy.__delim, __proxy.__escape);
-}
+    _LIBCPP_HIDE_FROM_ABI
+    explicit __quoted_proxy(basic_string<_CharT, _Traits, _Allocator>& __s, _CharT __d, _CharT __e)
+        : __string_(__s), __delim_(__d), __escape_(__e) {}
 
-//  extractor for non-const basic_string& proxies
-template <class _CharT, class _Traits, class _Allocator>
-_LIBCPP_INLINE_VISIBILITY
-basic_istream<_CharT, _Traits>& operator>>(
-        basic_istream<_CharT, _Traits>& __is,
-        const __quoted_proxy<_CharT, _Traits, _Allocator> & __proxy)
-{
-    return __quoted_input ( __is, __proxy.__string, __proxy.__delim, __proxy.__escape );
+    friend _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
+    operator<<(basic_ostream<_CharT, _Traits>& __os, const __quoted_proxy& __p) {
+        return std::__quoted_output(__os, __p.__string_.data(), __p.__string_.data() + __p.__string_.size(), __p.__delim_, __p.__escape_);
     }
 
-
-template <class _CharT>
-_LIBCPP_INLINE_VISIBILITY
-__quoted_output_proxy<_CharT, const _CharT *>
-quoted ( const _CharT *__s, _CharT __delim = _CharT('"'), _CharT __escape =_CharT('\\'))
-{
-    const _CharT *__end = __s;
-    while ( *__end ) ++__end;
-    return __quoted_output_proxy<_CharT, const _CharT *> ( __s, __end, __delim, __escape );
+    friend _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
+    operator>>(basic_istream<_CharT, _Traits>& __is, const __quoted_proxy& __p) {
+        return std::__quoted_input(__is, __p.__string_, __p.__delim_, __p.__escape_);
     }
-
+};
 
 template <class _CharT, class _Traits, class _Allocator>
-_LIBCPP_INLINE_VISIBILITY
-__quoted_output_proxy<_CharT, typename basic_string <_CharT, _Traits, _Allocator>::const_iterator>
-__quoted ( const basic_string <_CharT, _Traits, _Allocator> &__s, _CharT __delim = _CharT('"'), _CharT __escape=_CharT('\\'))
+_LIBCPP_HIDE_FROM_ABI
+__quoted_output_proxy<_CharT, _Traits>
+__quoted(const basic_string<_CharT, _Traits, _Allocator>& __s, _CharT __delim = _CharT('"'), _CharT __escape = _CharT('\\'))
 {
-    return __quoted_output_proxy<_CharT,
-            typename basic_string <_CharT, _Traits, _Allocator>::const_iterator>
-                    ( __s.cbegin(), __s.cend (), __delim, __escape );
+    return __quoted_output_proxy<_CharT, _Traits>(__s.data(), __s.data() + __s.size(), __delim, __escape);
 }
 
 template <class _CharT, class _Traits, class _Allocator>
-_LIBCPP_INLINE_VISIBILITY
+_LIBCPP_HIDE_FROM_ABI
 __quoted_proxy<_CharT, _Traits, _Allocator>
-__quoted ( basic_string <_CharT, _Traits, _Allocator> &__s, _CharT __delim = _CharT('"'), _CharT __escape=_CharT('\\'))
+__quoted(basic_string<_CharT, _Traits, _Allocator>& __s, _CharT __delim = _CharT('"'), _CharT __escape = _CharT('\\'))
 {
-    return __quoted_proxy<_CharT, _Traits, _Allocator>( __s, __delim, __escape );
+    return __quoted_proxy<_CharT, _Traits, _Allocator>(__s, __delim, __escape);
 }
 
+#endif // _LIBCPP_STD_VER >= 11
 
 #if _LIBCPP_STD_VER > 11
 
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI
+auto quoted(const _CharT *__s, _CharT __delim = _CharT('"'), _CharT __escape = _CharT('\\'))
+{
+    const _CharT *__end = __s;
+    while (*__end) ++__end;
+    return __quoted_output_proxy<_CharT, void>(__s, __end, __delim, __escape);
+}
+
 template <class _CharT, class _Traits, class _Allocator>
-_LIBCPP_INLINE_VISIBILITY
-__quoted_output_proxy<_CharT, typename basic_string <_CharT, _Traits, _Allocator>::const_iterator>
-quoted ( const basic_string <_CharT, _Traits, _Allocator> &__s, _CharT __delim = _CharT('"'), _CharT __escape=_CharT('\\'))
+_LIBCPP_HIDE_FROM_ABI
+auto quoted(const basic_string<_CharT, _Traits, _Allocator>& __s, _CharT __delim = _CharT('"'), _CharT __escape = _CharT('\\'))
 {
-    return __quoted(__s, __delim, __escape);
+    return __quoted_output_proxy<_CharT, _Traits>(__s.data(), __s.data() + __s.size(), __delim, __escape);
 }
 
 template <class _CharT, class _Traits, class _Allocator>
-_LIBCPP_INLINE_VISIBILITY
-__quoted_proxy<_CharT, _Traits, _Allocator>
-quoted ( basic_string <_CharT, _Traits, _Allocator> &__s, _CharT __delim = _CharT('"'), _CharT __escape=_CharT('\\'))
+_LIBCPP_HIDE_FROM_ABI
+auto quoted(basic_string<_CharT, _Traits, _Allocator>& __s, _CharT __delim = _CharT('"'), _CharT __escape = _CharT('\\'))
 {
-    return __quoted(__s, __delim, __escape);
+    return __quoted_proxy<_CharT, _Traits, _Allocator>(__s, __delim, __escape);
 }
 
 template <class _CharT, class _Traits>
-__quoted_output_proxy<_CharT, const _CharT *, _Traits>
-quoted (basic_string_view <_CharT, _Traits> __sv,
-             _CharT __delim = _CharT('"'), _CharT __escape=_CharT('\\'))
+auto quoted(basic_string_view<_CharT, _Traits> __sv, _CharT __delim = _CharT('"'), _CharT __escape = _CharT('\\'))
 {
-    return __quoted_output_proxy<_CharT, const _CharT *, _Traits>
-         ( __sv.data(), __sv.data() + __sv.size(), __delim, __escape );
+    return __quoted_output_proxy<_CharT, _Traits>(__sv.data(), __sv.data() + __sv.size(), __delim, __escape);
 }
-#endif
+
+#endif // _LIBCPP_STD_VER > 11
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_IOMANIP

libcxx/test/std/input.output/iostream.format/quoted.manip/quoted_traits.compile.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11
+
+// <iomanip>
+
+// quoted
+
+#include <iomanip>
+#include <istream>
+#include <ostream>
+#include <string>
+#include <string_view>
+#include <type_traits>
+
+#include "test_allocator.h"
+#include "test_macros.h"
+
+template<class IS, class Q>
+decltype(std::declval<IS>() >> std::declval<Q>(), std::true_type())
+has_rightshift_impl(int) { return std::true_type(); }
+
+template<class IS, class Q>
+std::false_type
+has_rightshift_impl(long) { return std::false_type(); }
+
+template<class IS, class Q>
+struct HasRightShift : decltype(has_rightshift_impl<IS, Q>(0)) {};
+
+template<class OS, class Q>
+decltype(std::declval<OS>() << std::declval<Q>(), std::true_type())
+has_leftshift_impl(int) { return std::true_type(); }
+
+template<class OS, class Q>
+std::false_type
+has_leftshift_impl(long) { return std::false_type(); }
+
+template<class OS, class Q>
+struct HasLeftShift : decltype(has_leftshift_impl<OS, Q>(0)) {};
+
+template<class CharT>
+struct FakeCharTraits : std::char_traits<CharT> {};
+
+void test_string_literal()
+{
+  using Q = decltype(std::quoted("hello"));
+  static_assert( HasLeftShift<std::ostream&, Q>::value, "");
+  static_assert(!HasRightShift<std::istream&, Q>::value, "");
+  static_assert( HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, Q>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, Q>::value, "");
+
+#ifndef TEST_HAS_NO_WCHAR_T
+  using WQ = decltype(std::quoted(L"hello"));
+  static_assert( HasLeftShift<std::wostream&, WQ>::value, "");
+  static_assert(!HasRightShift<std::wistream&, WQ>::value, "");
+  static_assert( HasLeftShift<std::basic_ostream<wchar_t, FakeCharTraits<wchar_t>>&, WQ>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<wchar_t, FakeCharTraits<wchar_t>>&, WQ>::value, "");
+
+  static_assert(!HasLeftShift<std::ostream&, WQ>::value, "");
+  static_assert(!HasLeftShift<std::wostream&, Q>::value, "");
+#endif // TEST_HAS_NO_WCHAR_T
+}
+
+void test_std_string()
+{
+  std::string s = "hello";
+  const auto& cs = s;
+  using Q = decltype(std::quoted(s));
+  using CQ = decltype(std::quoted(cs));
+  static_assert( HasLeftShift<std::ostream&, Q>::value, "");
+  static_assert( HasRightShift<std::istream&, Q>::value, "");
+  static_assert( HasLeftShift<std::ostream&, CQ>::value, "");
+  static_assert(!HasRightShift<std::istream&, CQ>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, Q>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, Q>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, CQ>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, CQ>::value, "");
+
+  std::basic_string<char, FakeCharTraits<char>, test_allocator<char>> st = "hello";
+  const auto& cst = st;
+  using QT = decltype(std::quoted(st));
+  using CQT = decltype(std::quoted(cst));
+  static_assert(!HasLeftShift<std::ostream&, QT>::value, "");
+  static_assert(!HasRightShift<std::istream&, QT>::value, "");
+  static_assert(!HasLeftShift<std::ostream&, CQT>::value, "");
+  static_assert(!HasRightShift<std::istream&, CQT>::value, "");
+  static_assert( HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, QT>::value, "");
+  static_assert( HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, QT>::value, "");
+  static_assert( HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, CQT>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, CQT>::value, "");
+
+#ifndef TEST_HAS_NO_WCHAR_T
+  std::wstring ws = L"hello";
+  const auto& cws = ws;
+  using WQ = decltype(std::quoted(ws));
+  using CWQ = decltype(std::quoted(cws));
+  static_assert( HasLeftShift<std::wostream&, WQ>::value, "");
+  static_assert( HasRightShift<std::wistream&, WQ>::value, "");
+  static_assert( HasLeftShift<std::wostream&, CWQ>::value, "");
+  static_assert(!HasRightShift<std::wistream&, CWQ>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<wchar_t, FakeCharTraits<wchar_t>>&, WQ>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<wchar_t, FakeCharTraits<wchar_t>>&, WQ>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<wchar_t, FakeCharTraits<wchar_t>>&, CWQ>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<wchar_t, FakeCharTraits<wchar_t>>&, CWQ>::value, "");
+
+  static_assert(!HasLeftShift<std::ostream&, WQ>::value, "");
+  static_assert(!HasLeftShift<std::wostream&, Q>::value, "");  
+#endif // TEST_HAS_NO_WCHAR_T
+}
+
+void test_std_string_view()
+{
+  std::string_view s = "hello";
+  const auto& cs = s;
+  using Q = decltype(std::quoted(s));
+  using CQ = decltype(std::quoted(cs));
+  static_assert( HasLeftShift<std::ostream&, Q>::value, "");
+  static_assert(!HasRightShift<std::istream&, Q>::value, "");
+  static_assert( HasLeftShift<std::ostream&, CQ>::value, "");
+  static_assert(!HasRightShift<std::istream&, CQ>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, Q>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, Q>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, CQ>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, CQ>::value, "");
+
+  std::basic_string_view<char, FakeCharTraits<char>> st = "hello";
+  const auto& cst = st;
+  using QT = decltype(std::quoted(st));
+  using CQT = decltype(std::quoted(cst));
+  static_assert(!HasLeftShift<std::ostream&, QT>::value, "");
+  static_assert(!HasRightShift<std::istream&, QT>::value, "");
+  static_assert(!HasLeftShift<std::ostream&, CQT>::value, "");
+  static_assert(!HasRightShift<std::istream&, CQT>::value, "");
+  static_assert( HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, QT>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, QT>::value, "");
+  static_assert( HasLeftShift<std::basic_ostream<char, FakeCharTraits<char>>&, CQT>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<char, FakeCharTraits<char>>&, CQT>::value, "");
+
+#ifndef TEST_HAS_NO_WCHAR_T
+  std::wstring_view ws = L"hello";
+  const auto& cws = ws;
+  using WQ = decltype(std::quoted(ws));
+  using CWQ = decltype(std::quoted(cws));
+  static_assert( HasLeftShift<std::wostream&, WQ>::value, "");
+  static_assert(!HasRightShift<std::wistream&, WQ>::value, "");
+  static_assert( HasLeftShift<std::wostream&, CWQ>::value, "");
+  static_assert(!HasRightShift<std::wistream&, CWQ>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<wchar_t, FakeCharTraits<wchar_t>>&, WQ>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<wchar_t, FakeCharTraits<wchar_t>>&, WQ>::value, "");
+  static_assert(!HasLeftShift<std::basic_ostream<wchar_t, FakeCharTraits<wchar_t>>&, CWQ>::value, "");
+  static_assert(!HasRightShift<std::basic_istream<wchar_t, FakeCharTraits<wchar_t>>&, CWQ>::value, "");
+
+  static_assert(!HasLeftShift<std::ostream&, WQ>::value, "");
+  static_assert(!HasLeftShift<std::wostream&, Q>::value, "");  
+#endif // TEST_HAS_NO_WCHAR_T
+}