hash.c:1692
static int
env_replace_i(key, val, keys)
    VALUE key, val, keys;
{
    if (key != Qundef) {
	env_aset(Qnil, key, val);
	if (rb_ary_includes(keys, key)) {
	    rb_ary_delete(keys, key);
	}
    }
    return ST_CONTINUE;
}
