One VS2010 bug ? Allowing binding non-const reference to rvalue WITHOUT EVEN a warning?

Question

string foo() { return "hello"; }
int main() 
{
    //below should be illegal for binding a non-const (lvalue) reference to a rvalue
    string& tem  = foo();   

    //below should be the correct one as only const reference can be bind to rvalue(most important const)
    const string& constTem = foo();   
}

1. GCC is the good one to give a compile error: invalid initialization of non-const reference of type std::string& from a temporary of type std::string
2. VS2008 is not too bad as at least it gives a compile warning: warning C4239: nonstandard extension used : 'initializing' : conversion from std::string to std::string & A non-const reference may only be bound to an lvalue
3. Here comes the problematic one - VS2010(SP1) comples fine WITHOUT any error or warning, WHY ??!! I know rvalue reference in VS2010 can be used to bind with rvalue but I am NOT using &&, instead in the demo code, I was just using non-const lvalue reference !

Can somone help me explain the behavior of VS2010 here? Is it a bug !? Thanks

Answer 1

That is a known issue/feature of the VS compilers. They have always allowed that and there does not seem to be any push into removing that extension.

Answer 2

The compiler will issue an error with Disable Language Extensions turned on, and a warning at /W4. However, removing this code will break previously compiling code, and Microsoft is very reluctant to do that. This is also why they won't fix their SFINAE support.