1// Copyright Louis Dionne 2013-2022
2// Distributed under the Boost Software License, Version 1.0.
3// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
4
5#include <boost/hana/assert.hpp>
6#include <boost/hana/at.hpp>
7#include <boost/hana/fold_left.hpp>
8#include <boost/hana/tuple.hpp>
9namespace hana = boost::hana;
10
11//
12// Make sure that we can fold_left and take arguments by reference.
13//
14
15int main() {
16 // with state
17 {
18 auto xs = hana::make_tuple(1, 2, 3);
19 int state = 99;
20
21 int& three = hana::fold_left(xs, state, [](int&, int& i) -> int& {
22 return i;
23 });
24 BOOST_HANA_RUNTIME_CHECK(three == 3);
25 three = 10;
26 BOOST_HANA_RUNTIME_CHECK(hana::at_c<2>(xs) == 10);
27 }
28
29 // without state
30 {
31 auto xs = hana::make_tuple(1, 2, 3);
32
33 int& three = hana::fold_left(xs, [](int&, int& i) -> int& {
34 return i;
35 });
36 BOOST_HANA_RUNTIME_CHECK(three == 3);
37 three = 10;
38 BOOST_HANA_RUNTIME_CHECK(hana::at_c<2>(xs) == 10);
39 }
40}
41

source code of boost/libs/hana/test/fold_left/ref.cpp