xstrided_view.hpp

/***************************************************************************
 * Copyright (c) Johan Mabille, Sylvain Corlay and Wolf Vollprecht          *
 * Copyright (c) QuantStack                                                 *
 *                                                                          *
 * Distributed under the terms of the BSD 3-Clause License.                 *
 *                                                                          *
 * The full license is in the file LICENSE, distributed with this software. *
 ****************************************************************************/

#ifndef XTENSOR_STRIDED_VIEW_HPP
#define XTENSOR_STRIDED_VIEW_HPP

#include <algorithm>
#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>

#include <xtl/xsequence.hpp>
#include <xtl/xvariant.hpp>

#include "xexpression.hpp"
#include "xiterable.hpp"
#include "xlayout.hpp"
#include "xsemantic.hpp"
#include "xstorage.hpp"
#include "xstrided_view_base.hpp"
#include "xutils.hpp"

namespace xt
{
    /***************************
     * xstrided_view extension *
     ***************************/

    namespace extension
    {
        template <class Tag, class CT, class S, layout_type L, class FST>
        struct xstrided_view_base_impl;

        template <class CT, class S, layout_type L, class FST>
        struct xstrided_view_base_impl<xtensor_expression_tag, CT, S, L, FST>
        {
            using type = xtensor_empty_base;
        };

        template <class CT, class S, layout_type L, class FST>
        struct xstrided_view_base : xstrided_view_base_impl<xexpression_tag_t<CT>, CT, S, L, FST>
        {
        };

        template <class CT, class S, layout_type L, class FST>
        using xstrided_view_base_t = typename xstrided_view_base<CT, S, L, FST>::type;
    }

    template <layout_type L1, layout_type L2, class T>
    struct select_iterable_base
    {
        using type = std::conditional_t<L1 == L2 && L1 != layout_type::dynamic, xcontiguous_iterable<T>, xiterable<T>>;
    };

    template <layout_type L1, layout_type L2, class T>
    using select_iterable_base_t = typename select_iterable_base<L1, L2, T>::type;


    template <class CT, class S, layout_type L, class FST>
    class xstrided_view;

    template <class CT, class S, layout_type L, class FST>
    struct xcontainer_inner_types<xstrided_view<CT, S, L, FST>>
    {
        using xexpression_type = std::decay_t<CT>;
        using undecay_expression = CT;
        using reference = inner_reference_t<undecay_expression>;
        using const_reference = typename xexpression_type::const_reference;
        using size_type = typename xexpression_type::size_type;
        using shape_type = std::decay_t<S>;
        using undecay_shape = S;
        using storage_getter = FST;
        using inner_storage_type = typename storage_getter::type;
        using temporary_type = typename detail::xtype_for_shape<
            S>::template type<typename xexpression_type::value_type, xexpression_type::static_layout>;
        using storage_type = std::remove_reference_t<inner_storage_type>;
        static constexpr layout_type layout = L;
    };

    template <class CT, class S, layout_type L, class FST>
    struct xiterable_inner_types<xstrided_view<CT, S, L, FST>>
    {
        using inner_shape_type = std::decay_t<S>;
        using inner_strides_type = get_strides_t<inner_shape_type>;
        using inner_backstrides_type_type = inner_strides_type;

        using const_stepper = std::conditional_t<
            is_indexed_stepper<typename std::decay_t<CT>::stepper>::value,
            xindexed_stepper<const xstrided_view<CT, S, L, FST>, true>,
            xstepper<const xstrided_view<CT, S, L, FST>>>;

        using stepper = std::conditional_t<
            is_indexed_stepper<typename std::decay_t<CT>::stepper>::value,
            xindexed_stepper<xstrided_view<CT, S, L, FST>, false>,
            xstepper<xstrided_view<CT, S, L, FST>>>;
    };

    template <class CT, class S, layout_type L, class FST, class RHS>
    struct can_assign<xstrided_view<CT, S, L, FST>, RHS> : can_assign<CT, RHS>
    {
    };

    /*****************
     * xstrided_view *
     *****************/

    /**
     * @class xstrided_view
     * @brief View of an xexpression using strides
     *
     * The xstrided_view class implements a view utilizing an initial offset
     * and strides.
     *
     * @tparam CT the closure type of the \ref xexpression type underlying this view
     * @tparam L the layout of the strided view
     * @tparam S the strides type of the strided view
     * @tparam FST the flat storage type used for the strided view
     *
     * @sa strided_view, transpose
     */
    template <class CT, class S, layout_type L = layout_type::dynamic, class FST = detail::flat_storage_getter<CT, XTENSOR_DEFAULT_TRAVERSAL>>
    class xstrided_view
        : public xview_semantic<xstrided_view<CT, S, L, FST>>,
          public select_iterable_base_t<L, std::decay_t<CT>::static_layout, xstrided_view<CT, S, L, FST>>,
          private xstrided_view_base<xstrided_view<CT, S, L, FST>>,
          public extension::xstrided_view_base_t<CT, S, L, FST>
    {
    public:

        using self_type = xstrided_view<CT, S, L, FST>;
        using base_type = xstrided_view_base<self_type>;
        using semantic_base = xview_semantic<self_type>;
        using extension_base = extension::xstrided_view_base_t<CT, S, L, FST>;
        using expression_tag = typename extension_base::expression_tag;

        using xexpression_type = typename base_type::xexpression_type;
        using base_type::is_const;

        using value_type = typename base_type::value_type;
        using reference = typename base_type::reference;
        using const_reference = typename base_type::const_reference;
        using pointer = typename base_type::pointer;
        using const_pointer = typename base_type::const_pointer;
        using size_type = typename base_type::size_type;
        using difference_type = typename base_type::difference_type;

        using inner_storage_type = typename base_type::inner_storage_type;
        using storage_type = typename base_type::storage_type;
        using linear_iterator = typename storage_type::iterator;
        using const_linear_iterator = typename storage_type::const_iterator;
        using reverse_linear_iterator = std::reverse_iterator<linear_iterator>;
        using const_reverse_linear_iterator = std::reverse_iterator<const_linear_iterator>;

        using iterable_base = select_iterable_base_t<L, xexpression_type::static_layout, self_type>;
        using inner_shape_type = typename base_type::inner_shape_type;
        using inner_strides_type = typename base_type::inner_strides_type;
        using inner_backstrides_type = typename base_type::inner_backstrides_type;
        using shape_type = typename base_type::shape_type;
        using strides_type = typename base_type::strides_type;
        using backstrides_type = typename base_type::backstrides_type;

        using stepper = typename iterable_base::stepper;
        using const_stepper = typename iterable_base::const_stepper;

        using base_type::contiguous_layout;
        using base_type::static_layout;

        using temporary_type = typename xcontainer_inner_types<self_type>::temporary_type;
        using base_index_type = xindex_type_t<shape_type>;

        using data_alignment = xt_simd::container_alignment_t<storage_type>;
        using simd_type = xt_simd::simd_type<value_type>;
        using simd_value_type = xt_simd::simd_type<value_type>;
        using bool_load_type = typename base_type::bool_load_type;

        template <class CTA, class SA>
        xstrided_view(CTA&& e, SA&& shape, strides_type&& strides, std::size_t offset, layout_type layout) noexcept;

        xstrided_view(const xstrided_view& rhs) = default;

        self_type& operator=(const self_type&);

        template <class E>
        self_type& operator=(const xexpression<E>& e);

        template <class E>
        disable_xexpression<E, self_type>& operator=(const E& e);

        using base_type::backstrides;
        using base_type::dimension;
        using base_type::is_contiguous;
        using base_type::layout;
        using base_type::shape;
        using base_type::size;
        using base_type::strides;

        using base_type::operator();
        using base_type::at;
        using base_type::unchecked;
        using base_type::operator[];
        using base_type::data;
        using base_type::data_offset;
        using base_type::element;
        using base_type::expression;
        using base_type::storage;

        using base_type::broadcast_shape;
        using base_type::has_linear_assign;

        template <class T>
        void fill(const T& value);

        linear_iterator linear_begin();
        linear_iterator linear_end();
        const_linear_iterator linear_begin() const;
        const_linear_iterator linear_end() const;
        const_linear_iterator linear_cbegin() const;
        const_linear_iterator linear_cend() const;

        reverse_linear_iterator linear_rbegin();
        reverse_linear_iterator linear_rend();
        const_reverse_linear_iterator linear_rbegin() const;
        const_reverse_linear_iterator linear_rend() const;
        const_reverse_linear_iterator linear_crbegin() const;
        const_reverse_linear_iterator linear_crend() const;

        template <class ST, class STEP = stepper>
        disable_indexed_stepper_t<STEP> stepper_begin(const ST& shape);
        template <class ST, class STEP = stepper>
        disable_indexed_stepper_t<STEP> stepper_end(const ST& shape, layout_type l);

        template <class ST, class STEP = stepper>
        enable_indexed_stepper_t<STEP> stepper_begin(const ST& shape);
        template <class ST, class STEP = stepper>
        enable_indexed_stepper_t<STEP> stepper_end(const ST& shape, layout_type l);

        template <class ST, class STEP = const_stepper>
        disable_indexed_stepper_t<STEP> stepper_begin(const ST& shape) const;
        template <class ST, class STEP = const_stepper>
        disable_indexed_stepper_t<STEP> stepper_end(const ST& shape, layout_type l) const;

        template <class ST, class STEP = const_stepper>
        enable_indexed_stepper_t<STEP> stepper_begin(const ST& shape) const;
        template <class ST, class STEP = const_stepper>
        enable_indexed_stepper_t<STEP> stepper_end(const ST& shape, layout_type l) const;

        template <class requested_type>
        using simd_return_type = xt_simd::simd_return_type<value_type, requested_type>;

        template <class T, class R>
        using enable_simd_interface = std::enable_if_t<has_simd_interface<T>::value && L != layout_type::dynamic, R>;

        template <class align, class simd, class T = xexpression_type>
        enable_simd_interface<T, void> store_simd(size_type i, const simd& e);
        template <
            class align,
            class requested_type = value_type,
            std::size_t N = xt_simd::simd_traits<requested_type>::size,
            class T = xexpression_type>
        enable_simd_interface<T, simd_return_type<requested_type>> load_simd(size_type i) const;

        reference data_element(size_type i);
        const_reference data_element(size_type i) const;

        reference flat(size_type i);
        const_reference flat(size_type i) const;

        using container_iterator = std::
            conditional_t<is_const, typename storage_type::const_iterator, typename storage_type::iterator>;
        using const_container_iterator = typename storage_type::const_iterator;

        template <class E>
        using rebind_t = xstrided_view<E, S, L, typename FST::template rebind_t<E>>;

        template <class E>
        rebind_t<E> build_view(E&& e) const;

    private:

        container_iterator data_xbegin() noexcept;
        const_container_iterator data_xbegin() const noexcept;
        container_iterator data_xend(layout_type l, size_type offset) noexcept;
        const_container_iterator data_xend(layout_type l, size_type offset) const noexcept;

        template <class It>
        It data_xbegin_impl(It begin) const noexcept;

        template <class It>
        It data_xend_impl(It end, layout_type l, size_type offset) const noexcept;

        void assign_temporary_impl(temporary_type&& tmp);

        using base_type::set_offset;

        template <class C>
        friend class xstepper;
        friend class xview_semantic<self_type>;
        friend class xaccessible<self_type>;
        friend class xconst_accessible<self_type>;
        template <class D>
        friend class xaxis_iterator;
        template <class D>
        friend class xaxis_slice_iterator;
    };

    /**************************
     * xstrided_view builders *
     **************************/

    template <class T>
    using xstrided_slice = xtl::variant<
        T,

        xrange_adaptor<placeholders::xtuph, T, T>,
        xrange_adaptor<T, placeholders::xtuph, T>,
        xrange_adaptor<T, T, placeholders::xtuph>,

        xrange_adaptor<T, placeholders::xtuph, placeholders::xtuph>,
        xrange_adaptor<placeholders::xtuph, T, placeholders::xtuph>,
        xrange_adaptor<placeholders::xtuph, placeholders::xtuph, T>,

        xrange_adaptor<T, T, T>,
        xrange_adaptor<placeholders::xtuph, placeholders::xtuph, placeholders::xtuph>,

        xrange<T>,
        xstepped_range<T>,

        xall_tag,
        xellipsis_tag,
        xnewaxis_tag>;

    /**
     * @typedef xstrided_slice_vector
     * @brief vector of slices used to build a `xstrided_view`
     */
    using xstrided_slice_vector = std::vector<xstrided_slice<std::ptrdiff_t>>;

    template <layout_type L = layout_type::dynamic, class E, class S, class X>
    auto strided_view(E&& e, S&& shape, X&& stride, std::size_t offset = 0, layout_type layout = L) noexcept;

    template <class E>
    auto strided_view(E&& e, const xstrided_slice_vector& slices);

    /********************************
     * xstrided_view implementation *
     ********************************/

    /**
     * @name Constructor
     */
    //@{
    /**
     * Constructs an xstrided_view
     *
     * @param e the underlying xexpression for this view
     * @param shape the shape of the view
     * @param strides the strides of the view
     * @param offset the offset of the first element in the underlying container
     * @param layout the layout of the view
     */
    template <class CT, class S, layout_type L, class FST>
    template <class CTA, class SA>
    inline xstrided_view<CT, S, L, FST>::xstrided_view(
        CTA&& e,
        SA&& shape,
        strides_type&& strides,
        std::size_t offset,
        layout_type layout
    ) noexcept
        : base_type(std::forward<CTA>(e), std::forward<SA>(shape), std::move(strides), offset, layout)
    {
    }

    //@}

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::operator=(const self_type& rhs) -> self_type&
    {
        temporary_type tmp(rhs);
        return this->assign_temporary(std::move(tmp));
    }

    /**
     * @name Extended copy semantic
     */
    //@{
    /**
     * The extended assignment operator.
     */
    template <class CT, class S, layout_type L, class FST>
    template <class E>
    inline auto xstrided_view<CT, S, L, FST>::operator=(const xexpression<E>& e) -> self_type&
    {
        return semantic_base::operator=(e);
    }

    //@}

    template <class CT, class S, layout_type L, class FST>
    template <class E>
    inline auto xstrided_view<CT, S, L, FST>::operator=(const E& e) -> disable_xexpression<E, self_type>&
    {
        this->fill(e);
        return *this;
    }

    namespace xstrided_view_detail
    {
        template <class V, class T>
        inline void run_assign_temporary_impl(V& v, const T& t, std::true_type /* enable strided assign */)
        {
            strided_loop_assigner<true>::run(v, t);
        }

        template <class V, class T>
        inline void
        run_assign_temporary_impl(V& v, const T& t, std::false_type /* fallback to iterator assign */)
        {
            std::copy(t.cbegin(), t.cend(), v.begin());
        }
    }

    template <class CT, class S, layout_type L, class FST>
    inline void xstrided_view<CT, S, L, FST>::assign_temporary_impl(temporary_type&& tmp)
    {
        constexpr bool
            fast_assign = xassign_traits<xstrided_view<CT, S, L, FST>, temporary_type>::simd_strided_assign();
        xstrided_view_detail::run_assign_temporary_impl(*this, tmp, std::integral_constant<bool, fast_assign>{});
    }

    /**
     * @name Data
     */
    //@{

    /**
     * Fills the view with the given value.
     * @param value the value to fill the view with.
     */
    template <class CT, class S, layout_type L, class FST>
    template <class T>
    inline void xstrided_view<CT, S, L, FST>::fill(const T& value)
    {
        if (layout() != layout_type::dynamic)
        {
            std::fill(this->linear_begin(), this->linear_end(), value);
        }
        else
        {
            std::fill(this->begin(), this->end(), value);
        }
    }

    //@}

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::data_element(size_type i) -> reference
    {
        return storage()[i];
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::data_element(size_type i) const -> const_reference
    {
        return storage()[i];
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::flat(size_type i) -> reference
    {
        return storage()[i];
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::flat(size_type i) const -> const_reference
    {
        return storage()[i];
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_begin() -> linear_iterator
    {
        return this->storage().begin() + static_cast<std::ptrdiff_t>(data_offset());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_end() -> linear_iterator
    {
        return this->storage().begin() + static_cast<std::ptrdiff_t>(data_offset() + size());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_begin() const -> const_linear_iterator
    {
        return this->linear_cbegin();
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_end() const -> const_linear_iterator
    {
        return this->linear_cend();
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_cbegin() const -> const_linear_iterator
    {
        return this->storage().cbegin() + static_cast<std::ptrdiff_t>(data_offset());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_cend() const -> const_linear_iterator
    {
        return this->storage().cbegin() + static_cast<std::ptrdiff_t>(data_offset() + size());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_rbegin() -> reverse_linear_iterator
    {
        return reverse_linear_iterator(this->linear_begin());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_rend() -> reverse_linear_iterator
    {
        return reverse_linear_iterator(this->linear_end());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_rbegin() const -> const_reverse_linear_iterator
    {
        return this->linear_crbegin();
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_rend() const -> const_reverse_linear_iterator
    {
        return this->linear_crend();
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_crbegin() const -> const_reverse_linear_iterator
    {
        return const_reverse_linear_iterator(this->linear_cbegin());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::linear_crend() const -> const_reverse_linear_iterator
    {
        return const_reverse_linear_iterator(this->linear_cend());
    }

    /***************
     * stepper api *
     ***************/

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_begin(const ST& shape) -> disable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return stepper(this, data_xbegin(), offset);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_end(const ST& shape, layout_type l)
        -> disable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return stepper(this, data_xend(l, offset), offset);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_begin(const ST& shape) -> enable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return stepper(this, offset);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_end(const ST& shape, layout_type /*l*/)
        -> enable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return stepper(this, offset, true);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_begin(const ST& shape) const
        -> disable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return const_stepper(this, data_xbegin(), offset);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_end(const ST& shape, layout_type l) const
        -> disable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return const_stepper(this, data_xend(l, offset), offset);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_begin(const ST& shape) const
        -> enable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return const_stepper(this, offset);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class ST, class STEP>
    inline auto xstrided_view<CT, S, L, FST>::stepper_end(const ST& shape, layout_type /*l*/) const
        -> enable_indexed_stepper_t<STEP>
    {
        size_type offset = shape.size() - dimension();
        return const_stepper(this, offset, true);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class It>
    inline It xstrided_view<CT, S, L, FST>::data_xbegin_impl(It begin) const noexcept
    {
        return begin + static_cast<std::ptrdiff_t>(this->data_offset());
    }

    template <class CT, class S, layout_type L, class FST>
    template <class It>
    inline It
    xstrided_view<CT, S, L, FST>::data_xend_impl(It begin, layout_type l, size_type offset) const noexcept
    {
        return strided_data_end(*this, begin + std::ptrdiff_t(this->data_offset()), l, offset);
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::data_xbegin() noexcept -> container_iterator
    {
        return data_xbegin_impl(this->storage().begin());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::data_xbegin() const noexcept -> const_container_iterator
    {
        return data_xbegin_impl(this->storage().cbegin());
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::data_xend(layout_type l, size_type offset) noexcept
        -> container_iterator
    {
        return data_xend_impl(this->storage().begin(), l, offset);
    }

    template <class CT, class S, layout_type L, class FST>
    inline auto xstrided_view<CT, S, L, FST>::data_xend(layout_type l, size_type offset) const noexcept
        -> const_container_iterator
    {
        return data_xend_impl(this->storage().cbegin(), l, offset);
    }

    template <class CT, class S, layout_type L, class FST>
    template <class alignment, class simd, class T>
    inline auto xstrided_view<CT, S, L, FST>::store_simd(size_type i, const simd& e)
        -> enable_simd_interface<T, void>
    {
        using align_mode = driven_align_mode_t<alignment, data_alignment>;
        xt_simd::store_as(&(storage()[i]), e, align_mode());
    }

    template <class CT, class S, layout_type L, class FST>
    template <class alignment, class requested_type, std::size_t N, class T>
    inline auto xstrided_view<CT, S, L, FST>::load_simd(size_type i) const
        -> enable_simd_interface<T, simd_return_type<requested_type>>
    {
        using align_mode = driven_align_mode_t<alignment, data_alignment>;
        return xt_simd::load_as<requested_type>(&(storage()[i]), align_mode());
    }

    template <class CT, class S, layout_type L, class FST>
    template <class E>
    inline auto xstrided_view<CT, S, L, FST>::build_view(E&& e) const -> rebind_t<E>
    {
        inner_shape_type sh(this->shape());
        inner_strides_type str(this->strides());
        return rebind_t<E>(
            std::forward<E>(e),
            std::move(sh),
            std::move(str),
            base_type::data_offset(),
            this->layout()
        );
    }

    /*****************************************
     * xstrided_view builders implementation *
     *****************************************/

    /**
     * Construct a strided view from an xexpression, shape, strides and offset.
     *
     * @param e xexpression
     * @param shape the shape of the view
     * @param strides the new strides of the view
     * @param offset the offset of the first element in the underlying container
     * @param layout the new layout of the expression
     *
     * @tparam L the static layout type of the view (default: dynamic)
     * @tparam E type of xexpression
     * @tparam S strides type
     * @tparam X strides type
     *
     * @return the view
     */
    template <layout_type L, class E, class S, class X>
    inline auto strided_view(E&& e, S&& shape, X&& strides, std::size_t offset, layout_type layout) noexcept
    {
        using view_type = xstrided_view<xclosure_t<E>, S, L>;
        return view_type(std::forward<E>(e), std::forward<S>(shape), std::forward<X>(strides), offset, layout);
    }

    namespace detail
    {
        struct no_adj_strides_policy
        {
        protected:

            inline void resize(std::size_t)
            {
            }

            inline void set_fake_slice(std::size_t)
            {
            }

            template <class ST, class S>
            bool fill_args(
                const xstrided_slice_vector& /*slices*/,
                std::size_t /*sl_idx*/,
                std::size_t /*i*/,
                std::size_t /*old_shape*/,
                const ST& /*old_stride*/,
                S& /*shape*/,
                get_strides_t<S>& /*strides*/
            )
            {
                return false;
            }
        };
    }

    /**
     * Function to create a dynamic view from
     * an xexpression and an xstrided_slice_vector.
     *
     * @param e xexpression
     * @param slices the slice vector
     *
     * @return initialized strided_view according to slices
     *
     * @code{.cpp}
     * xt::xarray<double> a = {{1, 2, 3}, {4, 5, 6}};
     * xt::xstrided_slice_vector sv({xt::range(0, 1)});
     * sv.push_back(xt::range(0, 3, 2));
     * auto v = xt::strided_view(a, sv);
     * // ==> {{1, 3}}
     * @endcode
     *
     * You can also achieve the same with the following short-hand syntax:
     *
     * @code{.cpp}
     * xt::xarray<double> a = {{1, 2, 3}, {4, 5, 6}};
     * auto v = xt::strided_view(a, {xt::range(0, 1), xt::range(0, 3, 2)});
     * // ==> {{1, 3}}
     * @endcode
     */
    template <class E>
    inline auto strided_view(E&& e, const xstrided_slice_vector& slices)
    {
        detail::strided_view_args<detail::no_adj_strides_policy> args;
        args.fill_args(
            e.shape(),
            detail::get_strides<XTENSOR_DEFAULT_TRAVERSAL>(e),
            detail::get_offset<XTENSOR_DEFAULT_TRAVERSAL>(e),
            e.layout(),
            slices
        );
        using view_type = xstrided_view<xclosure_t<E>, decltype(args.new_shape)>;
        return view_type(
            std::forward<E>(e),
            std::move(args.new_shape),
            std::move(args.new_strides),
            args.new_offset,
            args.new_layout
        );
    }

    namespace detail
    {
        template <typename S>
        struct rebind_shape;

        template <std::size_t... X>
        struct rebind_shape<xt::fixed_shape<X...>>
        {
            using type = xt::fixed_shape<X...>;
        };

        template <class S>
        struct rebind_shape
        {
            using type = rebind_container_t<size_t, S>;
        };

        template <
            class S,
            std::enable_if_t<std::is_signed<get_value_type_t<typename std::decay<S>::type>>::value, bool> = true>
        inline void recalculate_shape_impl(S& shape, size_t size)
        {
            using value_type = get_value_type_t<typename std::decay_t<S>>;
            XTENSOR_ASSERT(std::count(shape.cbegin(), shape.cend(), -1) <= 1);
            auto iter = std::find(shape.begin(), shape.end(), -1);
            if (iter != std::end(shape))
            {
                const auto total = std::accumulate(shape.cbegin(), shape.cend(), -1, std::multiplies<int>{});
                const auto missing_dimension = size / total;
                (*iter) = static_cast<value_type>(missing_dimension);
            }
        }

        template <
            class S,
            std::enable_if_t<!std::is_signed<get_value_type_t<typename std::decay<S>::type>>::value, bool> = true>
        inline void recalculate_shape_impl(S&, size_t)
        {
        }

        template <class S>
        inline auto recalculate_shape(S&& shape, size_t size)
        {
            return recalculate_shape_impl(shape, size);
        }
    }

    template <layout_type L = XTENSOR_DEFAULT_TRAVERSAL, class E, class S>
    inline auto reshape_view(E&& e, S&& shape)
    {
        static_assert(
            L == layout_type::row_major || L == layout_type::column_major,
            "traversal has to be row or column major"
        );

        using shape_type = std::decay_t<decltype(shape)>;
        using unsigned_shape_type = typename detail::rebind_shape<shape_type>::type;
        get_strides_t<unsigned_shape_type> strides;

        detail::recalculate_shape(shape, e.size());
        xt::resize_container(strides, shape.size());
        compute_strides(shape, L, strides);
        constexpr auto computed_layout = std::decay_t<E>::static_layout == L ? L : layout_type::dynamic;
        using view_type = xstrided_view<
            xclosure_t<E>,
            unsigned_shape_type,
            computed_layout,
            detail::flat_adaptor_getter<xclosure_t<E>, L>>;
        return view_type(
            std::forward<E>(e),
            xtl::forward_sequence<unsigned_shape_type, S>(shape),
            std::move(strides),
            0,
            e.layout()
        );
    }

    /**
     * @deprecated
     * @brief Return a view on a container with a new shape
     *
     * Note: if you resize the underlying container, this view becomes
     * invalidated.
     *
     * @param e xexpression to reshape
     * @param shape new shape
     * @param order traversal order (optional)
     *
     * @return view on xexpression with new shape
     */
    template <layout_type L = XTENSOR_DEFAULT_TRAVERSAL, class E, class S>
    inline auto reshape_view(E&& e, S&& shape, layout_type /*order*/)
    {
        return reshape_view<L>(std::forward<E>(e), std::forward<S>(shape));
    }

    template <layout_type L = XTENSOR_DEFAULT_TRAVERSAL, class E, class I, std::size_t N>
    inline auto reshape_view(E&& e, const I (&shape)[N], layout_type order)
    {
        using shape_type = std::array<std::size_t, N>;
        return reshape_view<L>(std::forward<E>(e), xtl::forward_sequence<shape_type, decltype(shape)>(shape), order);
    }

    template <layout_type L = XTENSOR_DEFAULT_TRAVERSAL, class E, class I, std::size_t N>
    inline auto reshape_view(E&& e, const I (&shape)[N])
    {
        using shape_type = std::array<I, N>;
        return reshape_view<L>(std::forward<E>(e), xtl::forward_sequence<shape_type, decltype(shape)>(shape));
    }
}

#endif