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1 | // Copyright Louis Dionne 2013-2017 | |
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(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 | } |