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Diffstat (limited to 'boost/hana/fwd/difference.hpp')
-rw-r--r-- | boost/hana/fwd/difference.hpp | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/boost/hana/fwd/difference.hpp b/boost/hana/fwd/difference.hpp new file mode 100644 index 0000000000..74c8e9ccee --- /dev/null +++ b/boost/hana/fwd/difference.hpp @@ -0,0 +1,72 @@ +/*! +@file +Forward declares `boost::hana::difference`. + +@copyright Louis Dionne 2013-2016 +Distributed under the Boost Software License, Version 1.0. +(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) + */ + +#ifndef BOOST_HANA_FWD_DIFFERENCE_HPP +#define BOOST_HANA_FWD_DIFFERENCE_HPP + +#include <boost/hana/config.hpp> +#include <boost/hana/core/when.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! Returns the set-theoretic difference of two sets. + //! @relates hana::set + //! + //! Given two sets `xs` and `ys`, `difference(xs, ys)` is a new set + //! containing all the elements of `xs` that are _not_ contained in `ys`. + //! For any object `x`, the following holds: + //! @code + //! x ^in^ difference(xs, ys) if and only if x ^in^ xs && !(x ^in^ ys) + //! @endcode + //! + //! + //! @note + //! This operation is not commutative, i.e. `difference(xs, ys)` is not + //! necessarily the same as `difference(ys, xs)`. Indeed, consider the + //! case where `xs` is empty and `ys` isn't. Then, `difference(xs, ys)` + //! is empty but `difference(ys, xs)` is equal to `ys`. For the symmetric + //! version of this operation, see `symmetric_difference`. + //! + //! + //! @param xs + //! A set to remove values from. + //! + //! @param ys + //! The set whose values are removed from `xs`. + //! + //! + //! Example + //! ------- + //! @include example/difference.cpp + //! + //! + //! Benchmarks + //! ---------- + //! <div class="benchmark-chart" + //! style="min-width: 310px; height: 400px; margin: 0 auto" + //! data-dataset="benchmark.difference.compile.json"> + //! </div> +#ifdef BOOST_HANA_DOXYGEN_INVOKED + constexpr auto difference = [](auto&& xs, auto&& ys) { + return tag-dispatched; + }; +#else + template <typename S, typename = void> + struct difference_impl : difference_impl<S, when<true>> { }; + + struct difference_t { + template <typename Xs, typename Ys> + constexpr auto operator()(Xs&& xs, Ys&& ys) const; + }; + + constexpr difference_t difference{}; +#endif +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_FWD_DIFFERENCE_HPP |