Can't coerce UNKNOWN to string in substitution iterator at - line 11, <> line 12 (#1)
    (F) Certain types of SVs, in particular real symbol table entries
    (typeglobs), can't be forced to stop being what they are.  So you can't
    say things like:
    
        *foo += 1;
    
    You CAN say
    
        $foo = *foo;
        $foo += 1;
    
    but then $foo no longer contains a glob.