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// Copyright Louis Dionne 2013-2017
// 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.hpp>
#include <functional>
#include <iostream>
#include <string>
#include <type_traits>
#include <utility>
namespace hana = boost::hana;
using namespace hana::literals;
using namespace std::literals;
//////////////////////////////////////////////////////////////////////////////
// Welcome to Hana!
//
// You can play around and press 'Run' at the bottom of this file to compile
// and run this code.
//
// To get you started, here's a small JSON generator written with Hana
// (this is explained in the tutorial if you're interested):
//////////////////////////////////////////////////////////////////////////////
// 1. Define some utilities
template <typename Xs>
std::string join(Xs&& xs, std::string sep) {
return hana::fold(hana::intersperse(std::forward<Xs>(xs), sep), "", std::plus<>{});
}
std::string quote(std::string s) { return "\"" + s + "\""; }
template <typename T>
auto to_json(T const& x) -> decltype(std::to_string(x)) {
return std::to_string(x);
}
std::string to_json(char c) { return quote({c}); }
std::string to_json(std::string s) { return quote(s); }
// 2. Define how to print user-defined types
template <typename T>
std::enable_if_t<hana::Struct<T>::value,
std::string> to_json(T const& x) {
auto json = hana::transform(hana::keys(x), [&](auto name) {
auto const& member = hana::at_key(x, name);
return quote(hana::to<char const*>(name)) + " : " + to_json(member);
});
return "{" + join(std::move(json), ", ") + "}";
}
// 3. Define how to print Sequences
template <typename Xs>
std::enable_if_t<hana::Sequence<Xs>::value,
std::string> to_json(Xs const& xs) {
auto json = hana::transform(xs, [](auto const& x) {
return to_json(x);
});
return "[" + join(std::move(json), ", ") + "]";
}
// 4. Create your own types and make them compatible with Hana.
// This can be done intrusively or non-intrusively.
struct Car {
BOOST_HANA_DEFINE_STRUCT(Car,
(std::string, brand),
(std::string, model)
);
};
int main() {
// 5. Generate beautiful JSON without hassle. Enjoy!
auto cars = hana::make_tuple(
Car{"BMW", "Z3"},
Car{"Audi", "A4"},
Car{"Ferrari", "F40"},
Car{"Lamborghini", "Diablo"}
// ...
);
std::cout << to_json(cars) << std::endl;
}
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