80 lines
2.8 KiB
C++
80 lines
2.8 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::is_subset`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_FWD_IS_SUBSET_HPP
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#define BOOST_HANA_FWD_IS_SUBSET_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/when.hpp>
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#include <boost/hana/functional/infix.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! Returns whether a structure contains a subset of the keys of
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//! another structure.
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//! @ingroup group-Searchable
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//!
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//! Given two `Searchable`s `xs` and `ys`, `is_subset` returns a `Logical`
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//! representing whether `xs` is a subset of `ys`. In other words, it
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//! returns whether all the keys of `xs` are also present in `ys`. This
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//! method does not return whether `xs` is a _strict_ subset of `ys`; if
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//! `xs` and `ys` are equal, all the keys of `xs` are also present in
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//! `ys`, and `is_subset` returns true.
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//!
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//! @note
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//! For convenience, `is_subset` can also be applied in infix notation.
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//!
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//!
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//! Cross-type version of the method
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//! --------------------------------
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//! This method is tag-dispatched using the tags of both arguments.
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//! It can be called with any two `Searchable`s sharing a common
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//! `Searchable` embedding, as defined in the main documentation
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//! of the `Searchable` concept. When `Searchable`s with two different
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//! tags but sharing a common embedding are sent to `is_subset`, they
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//! are first converted to this common `Searchable` and the `is_subset`
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//! method of the common embedding is then used. Of course, the method
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//! can be overriden for custom `Searchable`s for efficieny.
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//!
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//! @note
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//! While cross-type dispatching for `is_subset` is supported, it is
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//! not currently used by the library because there are no models
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//! of `Searchable` with a common embedding.
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//!
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//!
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//! @param xs
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//! The structure to check whether it is a subset of `ys`.
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//!
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//! @param ys
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//! The structure to check whether it is a superset of `xs`.
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//!
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//!
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//! Example
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//! -------
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//! @include example/is_subset.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto is_subset = [](auto&& xs, auto&& ys) {
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return tag-dispatched;
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};
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#else
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template <typename S1, typename S2, typename = void>
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struct is_subset_impl : is_subset_impl<S1, S2, when<true>> { };
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struct is_subset_t {
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template <typename Xs, typename Ys>
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constexpr auto operator()(Xs&& xs, Ys&& ys) const;
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};
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constexpr auto is_subset = hana::infix(is_subset_t{});
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_IS_SUBSET_HPP
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