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/*!
@file
Forward declares `boost::hana::slice` and `boost::hana::slice_c`.
Copyright Louis Dionne 2013-2022
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_SLICE_HPP
#define BOOST_HANA_FWD_SLICE_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
#include <cstddef>
namespace boost { namespace hana {
//! Extract the elements of a `Sequence` at the given indices.
//! @ingroup group-Sequence
//!
//! Given an arbitrary sequence of `indices`, `slice` returns a new
//! sequence of the elements of the original sequence that appear at
//! those indices. In other words,
//! @code
//! slice([x1, ..., xn], [i1, ..., ik]) == [x_i1, ..., x_ik]
//! @endcode
//!
//! The indices do not have to be ordered or contiguous in any particular
//! way, but they must not be out of the bounds of the sequence. It is
//! also possible to specify the same index multiple times, in which case
//! the element at this index will be repeatedly included in the resulting
//! sequence.
//!
//!
//! @param xs
//! The sequence from which a subsequence is extracted.
//!
//! @param indices
//! A compile-time `Foldable` containing non-negative `IntegralConstant`s
//! representing the indices. The indices are 0-based, and they must all
//! be in bounds of the `xs` sequence. Note that any `Foldable` will
//! really do (no need for an `Iterable`, for example); the linearization
//! of the `indices` is used to determine the order of the elements
//! included in the slice.
//!
//!
//! Example
//! -------
//! @include example/slice.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto slice = [](auto&& xs, auto&& indices) {
return tag-dispatched;
};
#else
template <typename S, typename = void>
struct slice_impl : slice_impl<S, when<true>> { };
struct slice_t {
template <typename Xs, typename Indices>
constexpr auto operator()(Xs&& xs, Indices&& indices) const;
};
BOOST_HANA_INLINE_VARIABLE constexpr slice_t slice{};
#endif
//! Shorthand to `slice` a contiguous range of elements.
//! @ingroup group-Sequence
//!
//! `slice_c` is simply a shorthand to slice a contiguous range of
//! elements. In particular, `slice_c<from, to>(xs)` is equivalent to
//! `slice(xs, range_c<std::size_t, from, to>)`, which simply slices
//! all the elements of `xs` contained in the half-open interval
//! delimited by `[from, to)`. Like for `slice`, the indices used with
//! `slice_c` are 0-based and they must be in the bounds of the sequence
//! being sliced.
//!
//!
//! @tparam from
//! The index of the first element in the slice.
//!
//! @tparam to
//! One-past the index of the last element in the slice. It must hold
//! that `from <= to`.
//!
//!
//! Example
//! -------
//! @include example/slice_c.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
template <std::size_t from, std::size_t to>
constexpr auto slice_c = [](auto&& xs) {
return hana::slice(forwarded(xs), hana::range_c<std::size_t, from, to>);
};
#else
template <std::size_t from, std::size_t to>
struct slice_c_t;
template <std::size_t from, std::size_t to>
BOOST_HANA_INLINE_VARIABLE constexpr slice_c_t<from, to> slice_c{};
#endif
}} // end namespace boost::hana
#endif // !BOOST_HANA_FWD_SLICE_HPP
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