https://bugs.llvm.org/show_bug.cgi?id=32963
Bug ID: 32963
Summary: Incorrect implementation of LWG 2534
Product: libc++
Version: 4.0
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: zi...@kayari.org
CC: llvm-bugs@lists.llvm.org, mclow.li...@gmail.com
#include <iostream>
int main()
{
std::ostream& os = std::move(std::cout) << "http://wg21.link/lwg2534";;
os << '\n';
}
prog.cc:5:19: error: non-const lvalue reference to type 'basic_ostream<...>'
cannot bind to a temporary of type 'basic_ostream<...>'
std::ostream& os = std::move(std::cout) << "http://wg21.link/lwg2534";;
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The return type should be an lvalue reference.
The SFINAE constraint on the operator<< for rvalue streams also seem wrong.
This shouldn't compile because the constraint is not met:
#include <ostream>
struct X : std::ios_base { };
struct Y { };
template<typename T, typename U, typename = void>
struct is_streamable
: std::false_type { };
template<typename T, typename U>
struct is_streamable<T, U, decltype(void(), std::declval<T>() <<
std::declval<U>())>
: std::true_type { };
static_assert( !is_streamable<X, Y>::value, "" );
decltype(std::declval<X>() << std::declval<Y>()) f();
const auto& ff = f();
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