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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::remove_if`.
   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_REMOVE_IF_HPP
  11 #define BOOST_HANA_FWD_REMOVE_IF_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Remove all the elements of a monadic structure that satisfy some
  19     //! predicate.
  20     //! @ingroup group-MonadPlus
  21     //!
  22     //! Given a monadic structure `xs` and a unary predicate, `remove_if`
  23     //! returns a new monadic structure equal to `xs` without all its elements
  24     //! that satisfy the predicate. This is equivalent to `filter` with a
  25     //! negated predicate, i.e.
  26     //! @code
  27     //!     remove_if(xs, predicate) == filter(xs, negated predicated)
  28     //! @endcode
  29     //!
  30     //!
  31     //! Signature
  32     //! ---------
  33     //! Given a MonadPlus `M` and a predicate of type \f$ T \to Bool \f$ for
  34     //! some compile-time Logical `Bool`, the signature is
  35     //! \f$
  36     //!     \mathrm{remove\_if} : M(T) \times (T \to Bool) \to M(T)
  37     //! \f$
  38     //!
  39     //! @param xs
  40     //! A monadic structure to remove some elements from.
  41     //!
  42     //! @param predicate
  43     //! A unary predicate called as `predicate(x)`, where `x` is an element
  44     //! of the structure, and returning whether `x` should be removed from
  45     //! the structure. In the current version of the library, `predicate`
  46     //! must return a compile-time Logical.
  47     //!
  48     //!
  49     //! Example
  50     //! -------
  51     //! @include example/remove_if.cpp
  52 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  53     constexpr auto remove_if = [](auto&& xs, auto&& predicate) {
  54         return tag-dispatched;
  55     };
  56 #else
  57     template <typename M, typename = void>
  58     struct remove_if_impl : remove_if_impl<M, when<true>> { };
  59
  60     struct remove_if_t {
  61         template <typename Xs, typename Pred>
  62         constexpr auto operator()(Xs&& xs, Pred&& pred) const;
  63     };
  64
  65     constexpr remove_if_t remove_if{};
  66 #endif
  67 BOOST_HANA_NAMESPACE_END
  68
  69 #endif // !BOOST_HANA_FWD_REMOVE_IF_HPP