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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::not_equal`.
   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_NOT_EQUAL_HPP
  11 #define BOOST_HANA_FWD_NOT_EQUAL_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15 #include <boost/hana/detail/nested_to_fwd.hpp>
  16
  17
  18 BOOST_HANA_NAMESPACE_BEGIN
  19     //! Returns a `Logical` representing whether `x` is not equal to `y`.
  20     //! @ingroup group-Comparable
  21     //!
  22     //! The `not_equal` function can be called in two different ways. First,
  23     //! it can be called like a normal function:
  24     //! @code
  25     //!     not_equal(x, y)
  26     //! @endcode
  27     //!
  28     //! However, it may also be partially applied to an argument by using
  29     //! `not_equal.to`:
  30     //! @code
  31     //!     not_equal.to(x)(y) == not_equal(x, y)
  32     //! @endcode
  33     //!
  34     //! In other words, `not_equal.to(x)` is a function object that is
  35     //! equivalent to `partial(not_equal, x)`. This is provided to enhance
  36     //! the readability of some constructs, especially when using higher
  37     //! order algorithms.
  38     //!
  39     //!
  40     //! Signature
  41     //! ---------
  42     //! Given a Logical `Bool` and two Comparables `A` and `B` that
  43     //! share a common embedding, the signature is
  44     //! @f$ \mathtt{not\_equal} : A \times B \to Bool @f$.
  45     //!
  46     //! @param x, y
  47     //! Two objects to compare for inequality.
  48     //!
  49     //!
  50     //! Example
  51     //! -------
  52     //! @include example/not_equal.cpp
  53 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  54     constexpr auto not_equal = [](auto&& x, auto&& y) {
  55         return tag-dispatched;
  56     };
  57 #else
  58     template <typename T, typename U, typename = void>
  59     struct not_equal_impl : not_equal_impl<T, U, when<true>> { };
  60
  61     struct not_equal_t : detail::nested_to<not_equal_t> {
  62         template <typename X, typename Y>
  63         constexpr auto operator()(X&& x, Y&& y) const;
  64     };
  65
  66     constexpr not_equal_t not_equal{};
  67 #endif
  68 BOOST_HANA_NAMESPACE_END
  69
  70 #endif // !BOOST_HANA_FWD_NOT_EQUAL_HPP