/*
 *  call-seq:
 *     array.shift   ->   obj or nil
 *  
 *  Returns the first element of <i>self</i> and removes it (shifting all
 *  other elements down by one). Returns <code>nil</code> if the array
 *  is empty.
 *     
 *     args = [ "-m", "-q", "filename" ]
 *     args.shift   #=> "-m"
 *     args         #=> ["-q", "filename"]
 */

VALUE
rb_ary_shift(ary)
    VALUE ary;
{
    VALUE top;

    rb_ary_modify_check(ary);
    if (RARRAY(ary)->len == 0) return Qnil;
    top = RARRAY(ary)->ptr[0];
    ary_make_shared(ary);
    RARRAY(ary)->ptr++;         /* shift ptr */
    RARRAY(ary)->len--;

    return top;
}