ceph/src/boost/libs/hana/include/boost/hana/fwd/zip_shortest.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::zip_shortest`.
   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_ZIP_SHORTEST_HPP
  11 #define BOOST_HANA_FWD_ZIP_SHORTEST_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Zip one sequence or more.
  19     //! @ingroup group-Sequence
  20     //!
  21     //! Given `n` sequences `s1, ..., sn`, `zip_shortest` produces a sequence
  22     //! whose `i`-th element is a tuple of `(s1[i], ..., sn[i])`, where `sk[i]`
  23     //! denotes the `i`-th element of the `k`-th sequence. In other words,
  24     //! `zip_shortest` produces a sequence of the form
  25     //! @code
  26     //!     [
  27     //!         make_tuple(s1[0], ..., sn[0]),
  28     //!         make_tuple(s1[1], ..., sn[1]),
  29     //!         ...
  30     //!         make_tuple(s1[M], ..., sn[M])
  31     //!     ]
  32     //! @endcode
  33     //! where `M` is the length of the shortest sequence. Hence, the returned
  34     //! sequence stops when the shortest input sequence is exhausted. If you
  35     //! know that all the sequences you are about to zip have the same length,
  36     //! you should use `zip` instead, since it can be more optimized. Also
  37     //! note that it is an error to provide no sequence at all, i.e.
  38     //! `zip_shortest` expects at least one sequence.
  39     //!
  40     //!
  41     //! Example
  42     //! -------
  43     //! @include example/zip_shortest.cpp
  44 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  45     constexpr auto zip_shortest = [](auto&& x1, ..., auto&& xn) {
  46         return tag-dispatched;
  47     };
  48 #else
  49     template <typename S, typename = void>
  50     struct zip_shortest_impl : zip_shortest_impl<S, when<true>> { };
  51
  52     struct zip_shortest_t {
  53         template <typename Xs, typename ...Ys>
  54         constexpr auto operator()(Xs&& xs, Ys&& ...ys) const;
  55     };
  56
  57     constexpr zip_shortest_t zip_shortest{};
  58 #endif
  59 BOOST_HANA_NAMESPACE_END
  60
  61 #endif // !BOOST_HANA_FWD_ZIP_SHORTEST_HPP