libstdc++: Make std::istream_iterator copy ctor constexpr (LWG 3600)

As explained in LWG 3600, we never implemented a C++0x change that made
the copy constructor of std::istream_iterator defined as defaulted. That
would be an ABI break, so the resolution of LWG 3600 is to not require
it to be trivial, but just constexpr and conditionally noexcept. This
applies that resolution.

libstdc++-v3/ChangeLog:

	* include/bits/stream_iterator.h (istream_iterator): Add
	constexpr to copy constructor, as per LWG 3600.
	* testsuite/24_iterators/istream_iterator/cons/constexpr.cc:
	Check copy construction.

diff --git a/libstdc++-v3/include/bits/stream_iterator.h b/libstdc++-v3/include/bits/stream_iterator.h
index 298d4406afdd2f493352382bdb1fdbd4d0c9be87..9dc4a550be60aa2f3bb13c7e8d2234cbc347d24a 100644 (file)
--- a/libstdc++-v3/include/bits/stream_iterator.h
+++ b/libstdc++-v3/include/bits/stream_iterator.h
@@ -80,6 +80,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       : _M_stream(std::__addressof(__s)), _M_ok(true)
       { _M_read(); }
 
+      _GLIBCXX_CONSTEXPR
       istream_iterator(const istream_iterator& __obj)
       _GLIBCXX_NOEXCEPT_IF(is_nothrow_copy_constructible<_Tp>::value)
       : _M_stream(__obj._M_stream), _M_value(__obj._M_value),

diff --git a/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/constexpr.cc b/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/constexpr.cc
index 824cd93ecbe31d20c21b928c287a9c82095bcd84..95fda572d8e1321e1ed8cfa27dcea828cf27116e 100644 (file)
--- a/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/constexpr.cc
+++ b/libstdc++-v3/testsuite/24_iterators/istream_iterator/cons/constexpr.cc
@@ -24,5 +24,10 @@ int main()
 {
   __gnu_test::constexpr_default_constructible test;
   test.operator()<std::istream_iterator<char>>();
+
+  // LWG 3600. Making istream_iterator copy constructor trivial is an ABI break
+  __gnu_test::constexpr_single_value_constructible test2;
+  test2.operator()<std::istream_iterator<char>, std::istream_iterator<char>>();
+
   return 0;
 }