Adding upstream version 16.2.11+ds.upstream/16.2.11+dsupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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), "");
+}