/*
 *  call-seq:
 *     meth.arity    => fixnum
 *  
 *  Returns an indication of the number of arguments accepted by a
 *  method. Returns a nonnegative integer for methods that take a fixed
 *  number of arguments. For Ruby methods that take a variable number of
 *  arguments, returns -n-1, where n is the number of required
 *  arguments. For methods written in C, returns -1 if the call takes a
 *  variable number of arguments.
 *     
 *     class C
 *       def one;    end
 *       def two(a); end
 *       def three(*a);  end
 *       def four(a, b); end
 *       def five(a, b, *c);    end
 *       def six(a, b, *c, &d); end
 *     end
 *     c = C.new
 *     c.method(:one).arity     #=> 0
 *     c.method(:two).arity     #=> 1
 *     c.method(:three).arity   #=> -1
 *     c.method(:four).arity    #=> 2
 *     c.method(:five).arity    #=> -3
 *     c.method(:six).arity     #=> -3
 *     
 *     "cat".method(:size).arity      #=> 0
 *     "cat".method(:replace).arity   #=> 1
 *     "cat".method(:squeeze).arity   #=> -1
 *     "cat".method(:count).arity     #=> -1
 */

static VALUE
method_arity(method)
    VALUE method;
{
    struct METHOD *data;
    NODE *body;
    int n;

    Data_Get_Struct(method, struct METHOD, data);

    body = data->body;
    switch (nd_type(body)) {
      case NODE_CFUNC:
        if (body->nd_argc < 0) return INT2FIX(-1);
        return INT2FIX(body->nd_argc);
      case NODE_ZSUPER:
        return INT2FIX(-1);
      case NODE_ATTRSET:
        return INT2FIX(1);
      case NODE_IVAR:
        return INT2FIX(0);
      case NODE_BMETHOD:
        return proc_arity(body->nd_cval);
      case NODE_DMETHOD:
        return method_arity(body->nd_cval);
      default:
        body = body->nd_next;  /* skip NODE_SCOPE */
        if (nd_type(body) == NODE_BLOCK)
            body = body->nd_head;
        if (!body) return INT2FIX(0);
        n = body->nd_cnt;
        if (body->nd_opt || body->nd_rest != -1)
            n = -n-1;
        return INT2FIX(n);
    }
}