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hana/example/integral/logical/eval_if.cpp

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/*
@copyright Louis Dionne 2014
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#include <boost/hana/adapted/std_integral_constant.hpp>
#include <boost/hana/detail/constexpr.hpp>
#include <boost/hana/detail/static_assert.hpp>
#include <boost/hana/functional.hpp>
#include <boost/hana/type.hpp>
#include <type_traits>
using namespace boost::hana;
int main() {
//! [main]
BOOST_HANA_CONSTEXPR_LAMBDA auto safe_make_unsigned = [](auto t) {
return eval_if(trait<std::is_integral>(t),
[=](auto id) { return id(template_<std::make_unsigned_t>)(t); },
always(t)
);
};
BOOST_HANA_STATIC_ASSERT(safe_make_unsigned(type<void>) == type<void>);
BOOST_HANA_STATIC_ASSERT(safe_make_unsigned(type<int>) == type<unsigned int>);
//! [main]
}