projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Forward declares `boost::hana::duplicate`. | |
| 4 | ||
| 5 | @copyright Louis Dionne 2013-2016 | |
| 6 | Distributed under the Boost Software License, Version 1.0. | |
| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
| 8 | */ | |
| 9 | ||
| 10 | #ifndef BOOST_HANA_FWD_DUPLICATE_HPP | |
| 11 | #define BOOST_HANA_FWD_DUPLICATE_HPP | |
| 12 | ||
| 13 | #include <boost/hana/config.hpp> | |
| 14 | #include <boost/hana/core/when.hpp> | |
| 15 | ||
| 16 | ||
| 17 | BOOST_HANA_NAMESPACE_BEGIN | |
| 18 | //! Add an extra layer of comonadic context to a comonadic value. | |
| 19 | //! @ingroup group-Comonad | |
| 20 | //! | |
| 21 | //! Given a value already in a comonadic context, `duplicate` wraps this | |
| 22 | //! value with an additional layer of comonadic context. This can be seen | |
| 23 | //! as the dual operation to `flatten` from the Monad concept. | |
| 24 | //! | |
| 25 | //! | |
| 26 | //! Signature | |
| 27 | //! --------- | |
| 28 | //! Given a Comonad `W`, the signature is | |
| 29 | //! \f$ | |
| 30 | //! \mathtt{duplicate} : W(T) \to W(W(T)) | |
| 31 | //! \f$ | |
| 32 | //! | |
| 33 | //! @param w | |
| 34 | //! The value to wrap in an additional level of comonadic context. | |
| 35 | //! | |
| 36 | //! | |
| 37 | //! Example | |
| 38 | //! ------- | |
| 39 | //! @include example/duplicate.cpp | |
| 40 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
| 41 | constexpr auto duplicate = [](auto&& w) -> decltype(auto) { | |
| 42 | return tag-dispatched; | |
| 43 | }; | |
| 44 | #else | |
| 45 | template <typename W, typename = void> | |
| 46 | struct duplicate_impl : duplicate_impl<W, when<true>> { }; | |
| 47 | ||
| 48 | struct duplicate_t { | |
| 49 | template <typename W_> | |
| 50 | constexpr decltype(auto) operator()(W_&& w) const; | |
| 51 | }; | |
| 52 | ||
| 53 | constexpr duplicate_t duplicate{}; | |
| 54 | #endif | |
| 55 | BOOST_HANA_NAMESPACE_END | |
| 56 | ||
| 57 | #endif // !BOOST_HANA_FWD_DUPLICATE_HPP |