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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::min`.
   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_MIN_HPP
  11 #define BOOST_HANA_FWD_MIN_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Returns the smallest of its arguments according to the `less` ordering.
  19     //! @ingroup group-Orderable
  20     //!
  21     //!
  22     //! @todo
  23     //! We can't specify the signature right now, because the tag of the
  24     //! returned object depends on whether `x < y` or not. If we wanted to be
  25     //! mathematically correct, we should probably ask that `if_(cond, x, y)`
  26     //! returns a common data type of `x` and `y`, and then the behavior
  27     //! of `min` would follow naturally. However, I'm unsure whether this
  28     //! is desirable because that's a big requirement.
  29     //!
  30     //!
  31     //! Example
  32     //! -------
  33     //! @include example/min.cpp
  34 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  35     constexpr auto min = [](auto&& x, auto&& y) -> decltype(auto) {
  36         return tag-dispatched;
  37     };
  38 #else
  39     template <typename T, typename U, typename = void>
  40     struct min_impl : min_impl<T, U, when<true>> { };
  41
  42     struct min_t {
  43         template <typename X, typename Y>
  44         constexpr decltype(auto) operator()(X&& x, Y&& y) const;
  45     };
  46
  47     constexpr min_t min{};
  48 #endif
  49 BOOST_HANA_NAMESPACE_END
  50
  51 #endif // !BOOST_HANA_FWD_MIN_HPP