flatten!

/*
 *  call-seq:
 *     array.flatten! -> array or nil
 *     array.flatten!(level) -> array or nil
 *  
 *  Flattens _self_ in place.
 *  Returns <code>nil</code> if no modifications were made (i.e.,
 *  <i>array</i> contains no subarrays.)  If the optional <i>level</i>
 *  argument determines the level of recursion to flatten.
 *     
 *     a = [ 1, 2, [3, [4, 5] ] ]
 *     a.flatten!   #=> [1, 2, 3, 4, 5]
 *     a.flatten!   #=> nil
 *     a            #=> [1, 2, 3, 4, 5]
 *     a = [ 1, 2, [3, [4, 5] ] ]
 *     a.flatten!(1) #=> [1, 2, 3, [4, 5]]
 */

static VALUE
rb_ary_flatten_bang(argc, argv, ary)
    int argc;
    VALUE *argv;
    VALUE ary;
{
    int mod = 0, level = -1;
    VALUE result, lv;

    rb_scan_args(argc, argv, "01", &lv);
    if (!NIL_P(lv)) level = NUM2INT(lv);
    if (level == 0) return ary;

    result = flatten(ary, level, &mod);
    if (mod == 0) return Qnil;
    rb_ary_replace(ary, result);

    return ary;
}