82 lines
2.7 KiB
C++
82 lines
2.7 KiB
C++
/*!
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@file
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Forward declares `boost::hana::partition`.
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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_PARTITION_HPP
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#define BOOST_HANA_FWD_PARTITION_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/detail/nested_by_fwd.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! Partition a sequence based on a `predicate`.
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//! @ingroup group-Sequence
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//!
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//! Specifically, returns an unspecified `Product` whose first element is
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//! a sequence of the elements satisfying the predicate, and whose second
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//! element is a sequence of the elements that do not satisfy the predicate.
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//!
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//!
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//! Signature
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//! ---------
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//! Given a Sequence `S(T)`, an `IntegralConstant` `Bool` holding a value
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//! of type `bool`, and a predicate \f$ T \to Bool \f$, `partition` has
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//! the following signature:
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//! \f[
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//! \mathtt{partition} : S(T) \times (T \to Bool) \to S(T) \times S(T)
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//! \f]
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//!
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//! @param xs
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//! The sequence to be partitioned.
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//!
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//! @param predicate
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//! A function called as `predicate(x)` for each element `x` in the
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//! sequence, and returning whether `x` should be added to the sequence
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//! in the first component or in the second component of the resulting
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//! pair. In the current version of the library, `predicate` must return
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//! an `IntegralConstant` holding a value convertible to `bool`.
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//!
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//!
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//! Syntactic sugar (`partition.by`)
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//! --------------------------------
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//! `partition` can be called in an alternate way, which provides a nice
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//! syntax in some cases where the predicate is short:
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//! @code
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//! partition.by(predicate, xs) == partition(xs, predicate)
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//! partition.by(predicate) == partition(-, predicate)
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//! @endcode
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//!
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//! where `partition(-, predicate)` denotes the partial application of
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//! `partition` to `predicate`.
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//!
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//!
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//! Example
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//! -------
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//! @include example/partition.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto partition = [](auto&& xs, auto&& predicate) {
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return tag-dispatched;
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};
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#else
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template <typename S, typename = void>
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struct partition_impl : partition_impl<S, when<true>> { };
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struct partition_t : detail::nested_by<partition_t> {
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template <typename Xs, typename Pred>
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constexpr auto operator()(Xs&& xs, Pred&& pred) const;
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};
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constexpr partition_t partition{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_PARTITION_HPP
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