Remove operator<<(rvalue, T)

For MSVC this was a better than the rvalue->lvalue conversion

fmt/format.h

@@ -155,24 +155,6 @@ typedef __int64          intmax_t;
 # endif
 #endif
 
-#ifndef FMT_USE_OSTREAM_RVALUE
-// If non-zero, enables operator<< for BasicWriter&&, such that things like
-//  std::string s = (MemoryWriter() << "i = " << i).str();
-// are possible.
-//
-// (See: http://cplusplus.github.io/LWG/lwg-active.html#1203)
-//
-// XXX:
-//  I don't know if FMT_USE_RVALUE_REFERENCES is the correct way to enable
-//  this... It works for g++ 6.3 and VC15, though.
-//
-# if FMT_USE_RVALUE_REFERENCES
-#  define FMT_USE_OSTREAM_RVALUE 1
-# else
-#  define FMT_USE_OSTREAM_RVALUE 0
-# endif
-#endif
-
 // Check if exceptions are disabled.
 #if defined(__GNUC__) && !defined(__EXCEPTIONS)
 # define FMT_EXCEPTIONS 0
@@ -2463,8 +2445,6 @@ class SystemError : public internal::RuntimeError {
 FMT_API void format_system_error(fmt::Writer &out, int error_code,
                                  fmt::StringRef message) FMT_NOEXCEPT;
 
-class BasicWriterBase {};
-
 /**
   \rst
   This template provides operations for formatting and writing data into
@@ -2484,7 +2464,7 @@ class BasicWriterBase {};
   \endrst
  */
 template <typename Char>
-class BasicWriter : public BasicWriterBase {
+class BasicWriter {
  private:
   // Output buffer.
   Buffer<Char> &buffer_;
@@ -2929,25 +2909,6 @@ inline BasicWriter<Char> &operator<<(
 }
 #endif
 
-#if FMT_USE_OSTREAM_RVALUE
-// http://cplusplus.github.io/LWG/lwg-active.html#1203
-//
-// For:
-// std::string s = (MemoryWriter() << "i = " << i).str();
-template <
-  typename WriterT,
-  typename T,
-  typename = typename std::enable_if<
-    !std::is_lvalue_reference<WriterT>::value
-      && std::is_base_of<BasicWriterBase, WriterT>::value
-  >::type
->
-inline WriterT &&operator<<(WriterT &&w, const T &value) {
-  w << value;
-  return std::move(w);
-}
-#endif
-
 template <typename Char>
 template <typename StrChar>
 typename BasicWriter<Char>::CharPtr BasicWriter<Char>::write_str(

test/format-test.cc

@@ -534,10 +534,6 @@ TEST(WriterTest, Stream) {
   //w << std::wstring(wcs);
   w << fmt::StrFormatSpec<wchar_t>(wcs, 3, ' ');
 #endif
-
-#if FMT_USE_OSTREAM_RVALUE
-  EXPECT_EQ("i = 123", (MemoryWriter() << "i = " << 123).str());
-#endif
 }
 
 TEST(WWriterTest, Stream) {
@@ -576,10 +572,6 @@ TEST(WWriterTest, Stream) {
   EXPECT_EQ(L"ncs", (WMemoryWriter() << fmt::StringRef(ncs)).str());
   EXPECT_EQ(L"ncs", (WMemoryWriter() << std::string(ncs)).str());
   EXPECT_EQ(L"ncs", (WMemoryWriter() << fmt::StrFormatSpec<char>(ncs, 3, ' ')).str());
-
-#if FMT_USE_OSTREAM_RVALUE
-  EXPECT_EQ(L"i = 123", (WMemoryWriter() << L"i = " << 123).str());
-#endif
 }
 
 TEST(ArrayWriterTest, Ctor) {

test/ostream-test.cc

@@ -145,11 +145,6 @@ TEST(OStreamTest, WriteUserDefinedTypeToOStream) {
   w << "The answer is " << u;
   fmt::internal::write(os, w);
   EXPECT_EQ("The answer is 42", os.str());
-
-#if FMT_USE_OSTREAM_RVALUE
-  EXPECT_EQ("The answer is 42",
-    (fmt::MemoryWriter() << "The answer is " << UserDefinedTest()).str());
-#endif
 }
 
 TEST(OStreamTest, WriteToOStreamMaxSize) {