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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::take_front` and `boost::hana::take_front_c`.
   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_TAKE_FRONT_HPP
  11 #define BOOST_HANA_FWD_TAKE_FRONT_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16 #include <cstddef>
  17
  18
  19 BOOST_HANA_NAMESPACE_BEGIN
  20     //! Returns the first `n` elements of a sequence, or the whole sequence
  21     //! if the sequence has less than `n` elements.
  22     //! @ingroup group-Sequence
  23     //!
  24     //! Given a `Sequence` `xs` and an `IntegralConstant` `n`, `take_front(xs, n)`
  25     //! is a new sequence containing the first `n` elements of `xs`, in the
  26     //! same order. If `length(xs) <= n`, the whole sequence is returned and
  27     //! no error is triggered.
  28     //!
  29     //!
  30     //! @param xs
  31     //! The sequence to take the elements from.
  32     //!
  33     //! @param n
  34     //! A non-negative `IntegralConstant` representing the number of elements
  35     //! to keep in the resulting sequence.
  36     //!
  37     //!
  38     //! Example
  39     //! -------
  40     //! @include example/take_front.cpp
  41 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  42     constexpr auto take_front = [](auto&& xs, auto const& n) {
  43         return tag-dispatched;
  44     };
  45 #else
  46     template <typename S, typename = void>
  47     struct take_front_impl : take_front_impl<S, when<true>> { };
  48
  49     struct take_front_t {
  50         template <typename Xs, typename N>
  51         constexpr auto operator()(Xs&& xs, N const& n) const;
  52     };
  53
  54     constexpr take_front_t take_front{};
  55 #endif
  56
  57     //! Equivalent to `take_front`; provided for convenience.
  58     //! @ingroup group-Sequence
  59     //!
  60     //!
  61     //! Example
  62     //! -------
  63     //! @include example/take_front_c.cpp
  64 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  65     template <std::size_t n>
  66     constexpr auto take_front_c = [](auto&& xs) {
  67         return hana::take_front(forwarded(xs), hana::size_c<n>);
  68     };
  69 #else
  70     template <std::size_t n>
  71     struct take_front_c_t;
  72
  73     template <std::size_t n>
  74     constexpr take_front_c_t<n> take_front_c{};
  75 #endif
  76 BOOST_HANA_NAMESPACE_END
  77
  78 #endif // !BOOST_HANA_FWD_TAKE_FRONT_HPP