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35cdf3b83a
This is done because the resulting macros are much more straightforward to debug when a user makes a mistake. Also, it avoids pulling yet another dependency. Also added some general purpose macros in detail/preprocessor.hpp.
103 lines
2.2 KiB
C++
103 lines
2.2 KiB
C++
/*
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@copyright Louis Dionne 2015
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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// Make sure `assert` always triggers an assertion
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#ifdef NDEBUG
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# undef NDEBUG
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#endif
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#include <cassert>
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#include <iostream>
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#include <string>
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#include <boost/hana/ext/std/type_traits.hpp>
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//! [includes]
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#include <boost/hana.hpp>
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using namespace boost::hana;
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//! [includes]
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using namespace boost::hana::literals;
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int main() {
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//! [animals]
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struct Fish { std::string name; };
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struct Cat { std::string name; };
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struct Dog { std::string name; };
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auto animals = make_tuple(Fish{"Nemo"}, Cat{"Garfield"}, Dog{"Snoopy"});
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//! [animals]
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//! [algorithms]
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// Access tuple elements with operator[] instead of std::get.
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Cat garfield = animals[1_c];
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// Perform high level algorithms on tuples (this is like std::transform)
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auto names = transform(animals, [](auto a) {
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return a.name;
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});
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assert(reverse(names) == make_tuple("Snoopy", "Garfield", "Nemo"));
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//! [algorithms]
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//! [type-level]
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auto animal_types = make_tuple(type<Fish*>, type<Cat&>, type<Dog>);
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auto no_pointers = remove_if(animal_types, [](auto a) {
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return traits::is_pointer(a);
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});
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static_assert(no_pointers == make_tuple(type<Cat&>, type<Dog>), "");
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//! [type-level]
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//! [has_name]
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auto has_name = is_valid([](auto&& x) -> decltype((void)x.name) { });
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static_assert(has_name(garfield), "");
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static_assert(!has_name(1), "");
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//! [has_name]
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#if 0
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//! [screw_up]
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auto serialize = [](std::ostream& os, auto const& object) {
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for_each(os, [&](auto member) {
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// ^^ oopsie daisy!
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os << member << std::endl;
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});
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};
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//! [screw_up]
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#endif
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//! [serialization]
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// 1. Give introspection capabilities to 'Person'
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struct Person {
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BOOST_HANA_DEFINE_STRUCT(Person,
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(std::string, name),
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(int, age)
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);
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};
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// 2. Write a generic serializer (bear with std::ostream for the example)
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auto serialize = [](std::ostream& os, auto const& object) {
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for_each(members(object), [&](auto member) {
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os << member << std::endl;
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});
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};
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// 3. Use it
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Person john{"John", 30};
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serialize(std::cout, john);
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// output:
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// John
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// 30
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//! [serialization]
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}
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