returning 'ref inout(T)' - not an lvalue?

[bitwise via Digitalmars-d-learn]

Compiling the code below gives these errors:

main.d(92): Error: 
cast(inout(int))this.list.data[cast(uint)(this.pos + i)] is not 
an lvalue
main.d(101): Error: template instance 
main.Iterator!(const(List!int)) error instantiating
main.d(108): instantiated from here: first!(const(List!int))

struct Iterator(C)
{
     C list;
     int pos;
	
     alias T = typeof(list.data[0]);

     this(C list, int pos) {
         this.list = list;
         this.pos = pos;
     }

     ref inout(T) opIndex(int i) inout {
         return list.data[pos + i];
     }
}

class List(T)
{
     T[] data = new T[1];

     auto first(this This)() {
         return Iterator!This(this, 0);
     }
}

int main(string[] argv)
{
     const(List!int) c;
     auto it = c.first;
}

Is it not possible to return a ref from an inout function?