Same as the primary operator+ for mixed std/bsl strings with an rvalue rhs.
Declared in <bslstl_string.h>
template<
class CHAR_TYPE,
class CHAR_TRAITS,
class ALLOC1,
class ALLOC2>
bsl::basic_string<CHAR_TYPE, CHAR_TRAITS, ALLOC2>
operator+(
std::basic_string<CHAR_TYPE, CHAR_TRAITS, ALLOC1> const& lhs,
bsl::basic_string<CHAR_TYPE, CHAR_TRAITS, ALLOC2>&& rhs);