You can assign to them, but it is as useless as assigning to locals of
a function.  Probably should just be disallowed.  When combined with $()
[which is actually just an arg] it is especially confusing.

2:
What do you think about this code ?
Does it compile ?
What will be the result ?

void create()
{
  int data;
  string *tmp=({"a","b","c"});

  data=0;
  map_array(tmp,(: $(data)+=1 :) );
  write(""+data);
}

If the result is not 3, where goes that three addition ?