std::move of string literal - which compiler is correct?

Question

Given the following code:

#include 
void foo()
{
  std::string s(std::move(\"\"));
}

This compiles with apple clang (xcode 7)

Answer 1

This looks like a Visual Studio bug. This comes down to the std::move and if we look at the cppreference page it has the following signature:

template< class T >
typename std::remove_reference::type&& move( T&& t );

and it returns:

static_cast::type&&>(t) 

which matches the draft C++ standard section 20.2.4 forward/move helpers [forward].

Using the code I grabbed from here we can see the following example:

#include 

template
struct value_category {
    // Or can be an integral or enum value
    static constexpr auto value = "prvalue";
};

template
struct value_category {
    static constexpr auto value = "lvalue";
};

template
struct value_category {
    static constexpr auto value = "xvalue";
};

// Double parens for ensuring we inspect an expression,
// not an entity
#define VALUE_CATEGORY(expr) value_category::value


int main()
{   
    std::cout << VALUE_CATEGORY( static_cast::type&&>("") ) << std::endl ;

}

generates the following answer from gcc and clang using Wandbox:

xvalue

and this answer from Visual Studio using webcompiler:

lvalue

hence the error from Visual Studio for the original code:

You cannot bind an lvalue to an rvalue reference

when it attempt to bind the result of static_cast::type&&>(t) to std::remove_reference::type&& which is the return value of std::move.

I don't see any reason why the static_cast should generate an lvalue as it does in the Visual Studio case.