| 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/eval.hpp> |
| 7 | #include <boost/hana/extend.hpp> |
| 8 | #include <boost/hana/extract.hpp> |
| 9 | #include <boost/hana/lazy.hpp> |
| 10 | |
| 11 | #include <functional> |
| 12 | #include <istream> |
| 13 | #include <sstream> |
| 14 | namespace hana = boost::hana; |
| 15 | |
| 16 | |
| 17 | template <typename T> |
| 18 | T read_one(std::istream& s) { |
| 19 | T value; |
| 20 | s >> value; |
| 21 | return value; |
| 22 | } |
| 23 | |
| 24 | int main() { |
| 25 | std::stringstream s; |
| 26 | s << "1 2 3"; |
| 27 | |
| 28 | auto from_stream = hana::extend(hana::make_lazy(read_one<int>)(std::ref(t&: s)), [](auto i) { |
| 29 | return hana::eval(i) + 1; |
| 30 | }); |
| 31 | |
| 32 | BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 2); |
| 33 | BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 3); |
| 34 | BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 4); |
| 35 | } |
| 36 |