[patch] Make std::string default constructor conditionally noexcept

[Jonathan Wakely]

On 13/05/15 14:36 +0100, Jonathan Wakely wrote:
>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4383.html#2455
>
>Voted into the WP in Lenexa.
>
>We already did the right thing for vector, so only basic_string needs
>to change.
>
>Tested powerpc64le-linux, committed to trunk.

Also committed to gcc-5-branch.

>commit 634ed6e2d2ea4d69a29a8907044e6f68541d88aa
>Author: Jonathan Wakely <jwakely@redhat.com>
>Date:   Wed May 13 14:21:37 2015 +0100
>
>    	* include/bits/basic_string.h (basic_string::basic_string()): Make
>    	noexcept conditional on allocator (LWG 2455).
>
>diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
>index 3e3eef4..093f502 100644
>--- a/libstdc++-v3/include/bits/basic_string.h
>+++ b/libstdc++-v3/include/bits/basic_string.h
>@@ -377,7 +377,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>       /**
>        *  @brief  Default constructor creates an empty string.
>        */
>-      basic_string() _GLIBCXX_NOEXCEPT
>+      basic_string()
>+#if __cplusplus >= 201103L
>+      noexcept(is_nothrow_default_constructible<_Alloc>::value)
>+#endif
>       : _M_dataplus(_M_local_data())
>       { _M_set_length(0); }
>