[libcxx] Add string_view literals

[AntonBikineev]

Summary

This is an implementation of Marshall Clow's P0403 paper proposing an addition of user-defined literals for string_view:

inline namespace literals { inline namespace string_literals {
constexpr string_view    operator "" sv(const char* str, size_t len) noexcept;
constexpr u16string_view operator "" sv(const char16_t* str, size_t len) noexcept;
constexpr u32string_view operator "" sv(const char32_t* str, size_t len) noexcept;
constexpr wstring_view   operator "" sv(const wchar_t* str, size_t len) noexcept;
}}

[EricWF]

Which paper is this implementing?

Also please update the synopsis comment at the top of the header.

include/string_view

749

If this is new to C++17 then the new declarations should be guarded by #if _LIBCPP_VERSION > 14.

754

Please add inline _LIBCPP_INLINE_VISIBILITY to each of these declarations.

[AntonBikineev]

include/string_view

749

Eric, I was thinking about it, but the fact that the whole string_view code is not guarded by _LIBCPP_VERSION > 14 (I guess it's because it can be compiled with lower Standards just fine) stopped me from doing that. I'm still not sure though.

[EricWF]

include/string_view

749

Understandable. The decision to backport most of string_view was intentional.

However we shouldn't backport these, since the literal suffix is only supported by the compiler in C++17.

[AntonBikineev]

include/string_view

749

Agreed

[AntonBikineev]

Fixing typos...

[EricWF]

Please ping this once the Clang changes have been accepted. I'm just waiting on those to give this the final OK.

[AntonBikineev]

In D26830#619340, @EricWF wrote:

Please ping this once the Clang changes have been accepted. I'm just waiting on those to give this the final OK.

I don't have commit privileges to Clang either, so that patch is stuck. Could you commit there please?

[EricWF]

Alright. I committed the Clang changes. Just re-building now so I can test this.

include/string_view

780

// _LIBCPP_STD_VER > 14 comment please.

test/std/strings/string.view/string.view.literals/literal1.pass.cpp

17

What's the point of this test that literal.pass.cpp doesn't cover?

test/std/strings/string.view/string.view.literals/literal2.pass.cpp

17

What's the point of this test that literal.pass.cpp doesn't cover?

[EricWF]

test/std/strings/string.view/string.view.literals/literal3.pass.cpp

17

You can move this test into literal.pass.cpp but putting it at another function scope.

[EricWF]

This LGTM. I'll approve once I see the inline comments addressed.

test/std/strings/string.view/string.view.literals/literal.pass.cpp

11

This needs a // XFAIL: clang-3, gcc-4, apple-clang-7, apple-clang-8

[EricWF]

@AntonBikineev when will you be able to make he requested changes? I would like to land this ASAP.

[AntonBikineev]

In D26830#711870, @EricWF wrote:

@AntonBikineev when will you be able to make he requested changes? I would like to land this ASAP.

Will do that today

[AntonBikineev]

In D26830#711870, @EricWF wrote:

@AntonBikineev when will you be able to make he requested changes? I would like to land this ASAP.

Eric, have you looked at commit 7d32d2f5a1f39d4cae9469645faa74b647698001? This functionality has already been implemented by Marshall, we should abandon this patch.

[EricWF]

test/std/strings/string.view/string.view.literals/literal2.pass.cpp

17

Ping on this comment.

test/std/strings/string.view/string.view.literals/literal3.pass.cpp

17

Ping on this comment.

[EricWF]

@AntonBikineev Yeah, this should be abandoned. Sorry my mistake.

include/string_view

     return __do_string_hash(__val.data(), __val.data() + __val.size());
 }
 
+#if _LIBCPP_STD_VER > 14
+// Literal suffixes for basic_string_view [basic.string_view.literals]
+inline namespace literals
+{
+  inline namespace string_view_literals
+  {
+    inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+    string_view operator "" sv(const char* __str, size_t __len) _NOEXCEPT
+    {
+        return string_view(__str, __len);
+    }
+
+    inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+    u16string_view operator "" sv(const char16_t* __str, size_t __len) _NOEXCEPT
+    {
+        return u16string_view(__str, __len);
+    }
+
+    inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+    u32string_view operator "" sv(const char32_t* __str, size_t __len) _NOEXCEPT
+    {
+        return u32string_view(__str, __len);
+    }
+
+    inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+    wstring_view operator "" sv(const wchar_t* __str, size_t __len) _NOEXCEPT
+    {
+        return wstring_view(__str, __len);
+    }
+  } // namespace string_view_literals
+#endif
+
+} // namespace literals
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_STRING_VIEW

test/std/strings/string.view/string.view.literals/literal.pass.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+#include <string>
+#include <string_view>
+#include <cassert>
+
+int main()
+{
+    using namespace std::literals::string_view_literals;
+
+    static_assert ( std::is_same<decltype(   "Hi"sv), std::string_view>::value, "" );
+    static_assert ( std::is_same<decltype(  L"Hi"sv), std::wstring_view>::value, "" );
+    static_assert ( std::is_same<decltype(  u"Hi"sv), std::u16string_view>::value, "" );
+    static_assert ( std::is_same<decltype(  U"Hi"sv), std::u32string_view>::value, "" );
+
+    std::string_view foo;
+    std::wstring_view Lfoo;
+    std::u16string_view ufoo;
+    std::u32string_view Ufoo;
+
+    foo  =   ""sv;     assert( foo.size() == 0);
+    Lfoo =  L""sv;     assert(Lfoo.size() == 0);
+    ufoo =  u""sv;     assert(ufoo.size() == 0);
+    Ufoo =  U""sv;     assert(Ufoo.size() == 0);
+
+    foo  =   " "sv;     assert( foo.size() == 1);
+    Lfoo =  L" "sv;     assert(Lfoo.size() == 1);
+    ufoo =  u" "sv;     assert(ufoo.size() == 1);
+    Ufoo =  U" "sv;     assert(Ufoo.size() == 1);
+
+    foo  =   "ABC"sv;     assert( foo ==   "ABC");   assert( foo == std::string   (  "ABC"));
+    Lfoo =  L"ABC"sv;     assert(Lfoo ==  L"ABC");   assert(Lfoo == std::wstring  ( L"ABC"));
+    ufoo =  u"ABC"sv;     assert(ufoo ==  u"ABC");   assert(ufoo == std::u16string( u"ABC"));
+    Ufoo =  U"ABC"sv;     assert(Ufoo ==  U"ABC");   assert(Ufoo == std::u32string( U"ABC"));
+}

test/std/strings/string.view/string.view.literals/literal1.fail.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+#include <string_view>
+#include <cassert>
+
+int main()
+{
+    using std::string_view;
+
+    string_view foo  =   ""sv;  // should fail w/conversion operator not found
+}

test/std/strings/string.view/string.view.literals/literal1.pass.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+#include <string_view>
+#include <cassert>
+
+int main()
+{
+    using namespace std::literals;
+
+    std::string_view foo  =   ""sv;
+}

test/std/strings/string.view/string.view.literals/literal2.fail.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+#include <string_view>
+#include <cassert>
+
+int main()
+{
+    std::string_view foo  =   ""sv;  // should fail w/conversion operator not found
+}

test/std/strings/string.view/string.view.literals/literal2.pass.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+#include <string_view>
+#include <cassert>
+
+int main()
+{
+    using namespace std::literals::string_view_literals;
+
+    std::string_view foo  =   ""sv;
+}

test/std/strings/string.view/string.view.literals/literal3.pass.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+#include <string_view>
+#include <cassert>
+
+int main()
+{
+    using namespace std;
+
+    string_view foo  =   ""sv;
+}