replace #include <ios> in FBString.h with lighter #include <iosfwd>

Summary:
FBString.h doesn't really use any of the facilities defined in <ios>, such as the stream manipulators. No sense dragging it into FBString.h.

This could potentially break downstream users if they are not already including the io facilities they are using. It's unlikely though because the actual stream types (std::ostream, std::istream) and stream objects (std::cout, std::cin) are defined in other headers that #include <ios>.

Reviewed By: yfeldblum, Orvid

Differential Revision: D4886133

fbshipit-source-id: 56adb93280eeeef8b09320b30fb224d4f72707bf

folly/FBString.h

@@ -21,7 +21,7 @@
 
 #include <atomic>
 #include <cstddef>
-#include <ios>
+#include <iosfwd>
 #include <limits>
 #include <type_traits>
 
@@ -2643,13 +2643,13 @@ std::basic_istream<
     std::basic_istream<typename basic_fbstring<E, T, A, S>::value_type,
     typename basic_fbstring<E, T, A, S>::traits_type>& is,
     basic_fbstring<E, T, A, S>& str) {
-  typename std::basic_istream<E, T>::sentry sentry(is);
-  typedef std::basic_istream<typename basic_fbstring<E, T, A, S>::value_type,
-                             typename basic_fbstring<E, T, A, S>::traits_type>
-                        __istream_type;
-  typedef typename __istream_type::ios_base __ios_base;
+  typedef std::basic_istream<
+      typename basic_fbstring<E, T, A, S>::value_type,
+      typename basic_fbstring<E, T, A, S>::traits_type>
+      _istream_type;
+  typename _istream_type::sentry sentry(is);
   size_t extracted = 0;
-  auto err = __ios_base::goodbit;
+  auto err = _istream_type::goodbit;
   if (sentry) {
     auto n = is.width();
     if (n <= 0) {
@@ -2658,7 +2658,7 @@ std::basic_istream<
     str.erase();
     for (auto got = is.rdbuf()->sgetc(); extracted != size_t(n); ++extracted) {
       if (got == T::eof()) {
-        err |= __ios_base::eofbit;
+        err |= _istream_type::eofbit;
         is.width(0);
         break;
       }
@@ -2670,7 +2670,7 @@ std::basic_istream<
     }
   }
   if (!extracted) {
-    err |= __ios_base::failbit;
+    err |= _istream_type::failbit;
   }
   if (err) {
     is.setstate(err);
@@ -2687,28 +2687,31 @@ operator<<(
   typename basic_fbstring<E, T, A, S>::traits_type>& os,
     const basic_fbstring<E, T, A, S>& str) {
 #if _LIBCPP_VERSION
-  typename std::basic_ostream<
-    typename basic_fbstring<E, T, A, S>::value_type,
-    typename basic_fbstring<E, T, A, S>::traits_type>::sentry __s(os);
-  if (__s) {
+  typedef std::basic_ostream<
+      typename basic_fbstring<E, T, A, S>::value_type,
+      typename basic_fbstring<E, T, A, S>::traits_type>
+      _ostream_type;
+  typename _ostream_type::sentry _s(os);
+  if (_s) {
     typedef std::ostreambuf_iterator<
       typename basic_fbstring<E, T, A, S>::value_type,
       typename basic_fbstring<E, T, A, S>::traits_type> _Ip;
     size_t __len = str.size();
     bool __left =
-      (os.flags() & std::ios_base::adjustfield) == std::ios_base::left;
+        (os.flags() & _ostream_type::adjustfield) == _ostream_type::left;
     if (__pad_and_output(_Ip(os),
                          str.data(),
                          __left ? str.data() + __len : str.data(),
                          str.data() + __len,
                          os,
                          os.fill()).failed()) {
-      os.setstate(std::ios_base::badbit | std::ios_base::failbit);
+      os.setstate(_ostream_type::badbit | _ostream_type::failbit);
     }
   }
 #elif defined(_MSC_VER)
+  typedef decltype(os.precision()) streamsize;
   // MSVC doesn't define __ostream_insert
-  os.write(str.data(), std::streamsize(str.size()));
+  os.write(str.data(), static_cast<streamsize>(str.size()));
 #else
   std::__ostream_insert(os, str.data(), str.size());
 #endif