array.c:47
static inline void
rb_ary_modify_check(ary)
    VALUE ary;
{
    if (OBJ_FROZEN(ary)) rb_error_frozen("array");
    if (FL_TEST(ary, ARY_TMPLOCK))
	rb_raise(rb_eTypeError, "can't modify array during iteration");
    if (!OBJ_TAINTED(ary) && rb_safe_level() >= 4)
	rb_raise(rb_eSecurityError, "Insecure: can't modify array");
}
