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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:45:59 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:45:59 +0000 |
commit | 19fcec84d8d7d21e796c7624e521b60d28ee21ed (patch) | |
tree | 42d26aa27d1e3f7c0b8bd3fd14e7d7082f5008dc /src/boost/libs/hana/example/overview.cpp | |
parent | Initial commit. (diff) | |
download | ceph-19fcec84d8d7d21e796c7624e521b60d28ee21ed.tar.xz ceph-19fcec84d8d7d21e796c7624e521b60d28ee21ed.zip |
Adding upstream version 16.2.11+ds.upstream/16.2.11+dsupstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/boost/libs/hana/example/overview.cpp')
-rw-r--r-- | src/boost/libs/hana/example/overview.cpp | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/overview.cpp b/src/boost/libs/hana/example/overview.cpp new file mode 100644 index 000000000..37b802f3b --- /dev/null +++ b/src/boost/libs/hana/example/overview.cpp @@ -0,0 +1,59 @@ +// 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) + +// Make sure assert always triggers an assertion +#ifdef NDEBUG +# undef NDEBUG +#endif + +////////////////////////////////////////////////////////////////////////////// +// Important: Keep this file in sync with the Overview in the README +////////////////////////////////////////////////////////////////////////////// +#include <boost/hana.hpp> +#include <cassert> +#include <string> +namespace hana = boost::hana; +using namespace hana::literals; + +struct Fish { std::string name; }; +struct Cat { std::string name; }; +struct Dog { std::string name; }; + +int main() { + // Sequences capable of holding heterogeneous objects, and algorithms + // to manipulate them. + auto animals = hana::make_tuple(Fish{"Nemo"}, Cat{"Garfield"}, Dog{"Snoopy"}); + auto names = hana::transform(animals, [](auto a) { + return a.name; + }); + assert(hana::reverse(names) == hana::make_tuple("Snoopy", "Garfield", "Nemo")); + + // No compile-time information is lost: even if `animals` can't be a + // constant expression because it contains strings, its length is constexpr. + static_assert(hana::length(animals) == 3u, ""); + + // Computations on types can be performed with the same syntax as that of + // normal C++. Believe it or not, everything is done at compile-time. + auto animal_types = hana::make_tuple(hana::type_c<Fish*>, hana::type_c<Cat&>, hana::type_c<Dog*>); + auto animal_ptrs = hana::filter(animal_types, [](auto a) { + return hana::traits::is_pointer(a); + }); + static_assert(animal_ptrs == hana::make_tuple(hana::type_c<Fish*>, hana::type_c<Dog*>), ""); + + // And many other goodies to make your life easier, including: + // 1. Access to elements in a tuple with a sane syntax. + static_assert(animal_ptrs[0_c] == hana::type_c<Fish*>, ""); + static_assert(animal_ptrs[1_c] == hana::type_c<Dog*>, ""); + + // 2. Unroll loops at compile-time without hassle. + std::string s; + hana::int_c<10>.times([&]{ s += "x"; }); + // equivalent to s += "x"; s += "x"; ... s += "x"; + + // 3. Easily check whether an expression is valid. + // This is usually achieved with complex SFINAE-based tricks. + auto has_name = hana::is_valid([](auto&& x) -> decltype((void)x.name) { }); + static_assert(has_name(animals[0_c]), ""); + static_assert(!has_name(1), ""); +} |