Is returning uniform initialized reference valid?

Is this code sample valid?

using ref = char&;

ref foo(ref x) {
  return ref{x};
}

int main() {
  char a;
  foo(a);
  return 0;
}

seems that:

• clang 3.5 says YES


• 
  

  gcc 4.9 says NO

  
  

  
  main.cpp: In function 'char& foo(ref)':
  main.cpp:4:15: error: invalid cast of an rvalue expression of type 'char' to type 'ref {aka char&}'
     return ref{x};
                 ^
  
  

http://ift.tt/1Db7x0v

So which compiler is right? or is it unspecified?

It very easy so overcome gcc build error by:

1. 
   

   using parenthesis instead of braces

   
   

   
   ref foo(ref x) {
     return ref(x);
   }
   
   



2. 
   

   by naming returned value

   
   

   
   ref foo(ref x) {
     ref ret{x};
     return ret;
   }
   
   

option 1. breaks uniform initialization, option 2. adds useless line of code.

Similar question was already aked here: Why can't I initialize a reference in an initializer list with uniform initialization?

But mentioned pr50025 is fixed in gcc 4.9.

I know that above code sample is pretty useless, but I did it intentionally to point out the issue. In real life code problem can be hidden in a generic function like:

#include <utility>
template <typename Tp, typename... Us>
Tp bar(Us&&... us) {
  return Tp{std::forward<Us>(us)...};
}