106 lines
3.5 KiB
C++
106 lines
3.5 KiB
C++
|
/*!
|
||
|
|
@file
|
||
|
|
Forward declares `boost::hana::slice` and `boost::hana::slice_c`.
|
||
|
|
|
||
|
|
@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_SLICE_HPP
|
||
|
|
#define BOOST_HANA_FWD_SLICE_HPP
|
||
|
|
|
||
|
|
#include <boost/hana/config.hpp>
|
||
|
|
#include <boost/hana/core/when.hpp>
|
||
|
|
|
||
|
|
#include <cstddef>
|
||
|
|
|
||
|
|
|
||
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
||
|
|
//! 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;
|
||
|
|
};
|
||
|
|
|
||
|
|
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>
|
||
|
|
constexpr slice_c_t<from, to> slice_c{};
|
||
|
|
#endif
|
||
|
|
BOOST_HANA_NAMESPACE_END
|
||
|
|
|
||
|
|
#endif // !BOOST_HANA_FWD_SLICE_HPP
|