import std;
import std.range;
void main()
{
    int[] a = [3, 5, 7];
    foreach (i, ref ae; a.enumerate)
    {
     	writeln(i, " ", ae);
        ae = 6;
    }
    writeln(a);
    assert(a[].equal([6, 6, 6]));  // fails, a is in initial state
}


Why does the compiler allow such 'ref ae' loop, if the actual value is not a reference? Or it is a reference to hidden stack variable that was copied by enumerate from a during front()?