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