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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::take_while`.
   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_WHILE_HPP
  11 #define BOOST_HANA_FWD_TAKE_WHILE_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Take elements from a sequence while the `predicate` is satisfied.
  19     //! @ingroup group-Sequence
  20     //!
  21     //! Specifically, `take_while` returns a new sequence containing the
  22     //! longest prefix of `xs` in which all the elements satisfy the given
  23     //! predicate.
  24     //!
  25     //!
  26     //! @param xs
  27     //! The sequence to take elements from.
  28     //!
  29     //! @param predicate
  30     //! A function called as `predicate(x)`, where `x` is an element of the
  31     //! sequence, and returning a `Logical` representing whether `x` should be
  32     //! included in the resulting sequence. In the current version of the
  33     //! library, `predicate` has to return a `Constant Logical`.
  34     //!
  35     //!
  36     //! Example
  37     //! -------
  38     //! @include example/take_while.cpp
  39 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  40     constexpr auto take_while = [](auto&& xs, auto&& predicate) {
  41         return tag-dispatched;
  42     };
  43 #else
  44     template <typename S, typename = void>
  45     struct take_while_impl : take_while_impl<S, when<true>> { };
  46
  47     struct take_while_t {
  48         template <typename Xs, typename Pred>
  49         constexpr auto operator()(Xs&& xs, Pred&& pred) const;
  50     };
  51
  52     constexpr take_while_t take_while{};
  53 #endif
  54 BOOST_HANA_NAMESPACE_END
  55
  56 #endif // !BOOST_HANA_FWD_TAKE_WHILE_HPP