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