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Adding rank member to allow sfinae based on rank
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‎docs/source/index.rst‎

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@@ -69,6 +69,7 @@ for details.
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missing
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histogram
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random
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sfinae
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file_loading
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build-options
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pitfall

‎docs/source/sfinae.rst‎

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.. Copyright (c) 2016, Johan Mabille, Sylvain Corlay and Wolf Vollprecht
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Distributed under the terms of the BSD 3-Clause License.
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The full license is in the file LICENSE, distributed with this software.
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.. _histogram:
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SFINAE
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======
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Rank overload
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-------------
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All `xtensor`'s classes have a member ``rank`` that can be used
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to overload based on rank using *SFINAE*.
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Consider the following example:
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.. code-block:: cpp
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template <class E, std::enable_if_t<!xt::has_rank_t<E, 2>::value, int> = 0>
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inline E foo(E&& a)
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{
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... // act on object of flexible rank, or fixed rank != 2
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}
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template <class E, std::enable_if_t<xt::has_rank_t<E, 2>::value, int> = 0>
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inline E foo(E&& a)
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{
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... // act on object of fixed rank == 2
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}
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TEST(sfinae, rank_basic)
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{
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xt::xarray<size_t> a = {{9, 9}, {9, 9}};
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xt::xtensor<size_t, 1> b = {9, 9};
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xt::xtensor<size_t, 2> c = {{9, 9}, {9, 9}};
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foo(a); // flexible rank -> first overload
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foo(b); // fixed rank == 2 -> first overload
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foo(c); // fixed rank == 2 -> second overload
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}
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.. note::
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If one wants to test for more than a single value for ``rank``,
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one can use the default value ``SIZE_MAX`` used for flexible rank objects.
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For example, one could have the following overloads:
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.. code-block:: cpp
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// flexible rank
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template <class E, std::enable_if_t<xt::has_rank_t<E, SIZE_MAX>::value, int> = 0>
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inline E foo(E&& a);
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// fixed rank == 1
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template <class E, std::enable_if_t<xt::has_rank_t<E, 1>::value, int> = 0>
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inline E foo(E&& a);
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// fixed rank == 2
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template <class E, std::enable_if_t<xt::has_rank_t<E, 2>::value, int> = 0>
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inline E foo(E&& a);
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Note that fixed ranks other than 1 and 2 will raise a compiler error.
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Of course, if one wants a more limited scope, one could also do the following:
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.. code-block:: cpp
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// flexible rank
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inline void foo(xt::xarray<double>& a);
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// fixed rank == 1
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inline void foo(xt::xtensor<double,1>& a);
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// fixed rank == 2
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inline void foo(xt::xtensor<double,2>& a);

‎include/xtensor/xarray.hpp‎

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using inner_backstrides_type = typename base_type::inner_backstrides_type;
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using temporary_type = typename semantic_base::temporary_type;
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using expression_tag = Tag;
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constexpr static std::size_t rank = SIZE_MAX;
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xarray_container();
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explicit xarray_container(const shape_type& shape, layout_type l = L);

‎include/xtensor/xfixed.hpp‎

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namespace detail
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{
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/**************************************************************************************
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The following is something we can currently only dream about -- for when we drop
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The following is something we can currently only dream about -- for when we drop
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support for a lot of the old compilers (e.g. GCC 4.9, MSVC 2017 ;)
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template <class T>
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* with tensor semantic and fixed dimension
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*
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* @tparam ET The type of the elements.
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* @tparam S The xshape template paramter of the container.
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* @tparam S The xshape template paramter of the container.
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* @tparam L The layout_type of the tensor.
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* @tparam SH Wether the tensor can be used as a shared expression.
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* @tparam Tag The expression tag.
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using expression_tag = Tag;
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constexpr static std::size_t N = std::tuple_size<shape_type>::value;
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constexpr static std::size_t rank = N;
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xfixed_container() = default;
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xfixed_container(const value_type& v);
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/**
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* Allocates an xfixed_container with shape S with values from a C array.
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* The type returned by get_init_type_t is raw C array ``value_type[X][Y][Z]`` for ``xt::xshape<X, Y, Z>``.
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* The type returned by get_init_type_t is raw C array ``value_type[X][Y][Z]`` for ``xt::xshape<X, Y, Z>``.
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* C arrays can be initialized with the initializer list syntax, but the size is checked at compile
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* time to prevent errors.
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* Note: for clang < 3.8 this is an initializer_list and the size is not checked at compile-or runtime.

‎include/xtensor/xtensor.hpp‎

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using inner_strides_type = typename base_type::inner_strides_type;
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using temporary_type = typename semantic_base::temporary_type;
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using expression_tag = Tag;
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constexpr static std::size_t rank = N;
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xtensor_container();
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xtensor_container(nested_initializer_list_t<value_type, N> t);
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std::fill(m_storage.begin(), m_storage.end(), e);
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return *this;
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}
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template <class EC, std::size_t N, layout_type L, class Tag>
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inline auto xtensor_view<EC, N, L, Tag>::storage_impl() noexcept -> storage_type&
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{

‎include/xtensor/xutils.hpp‎

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template <class ST>
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using inner_reference_t = typename inner_reference<ST>::type;
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/************
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* has_rank *
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************/
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template <class E, size_t N>
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struct has_rank
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{
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using type = std::integral_constant<bool, std::decay_t<E>::rank == N>;
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};
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template <class E, size_t N>
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using has_rank_t = typename has_rank<std::decay_t<E>, N>::type;
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}
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#endif

‎include/xtensor/xview.hpp‎

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using container_iterator = pointer;
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using const_container_iterator = const_pointer;
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constexpr static std::size_t rank = SIZE_MAX;
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// The FSL argument prevents the compiler from calling this constructor
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// instead of the copy constructor when sizeof...(SL) == 0.

‎test/CMakeLists.txt‎

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test_extended_xhistogram.cpp
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test_extended_xsort.cpp
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test_xchunked_array.cpp
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test_sfinae.cpp
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)
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if(nlohmann_json_FOUND)

‎test/test_sfinae.cpp‎

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/***************************************************************************
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* Copyright (c) Johan Mabille, Sylvain Corlay and Wolf Vollprecht *
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* Copyright (c) QuantStack *
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* *
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* Distributed under the terms of the BSD 3-Clause License. *
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* *
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* The full license is in the file LICENSE, distributed with this software. *
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****************************************************************************/
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#include <complex>
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#include <limits>
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#include "gtest/gtest.h"
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#include "xtensor/xtensor.hpp"
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#include "xtensor/xarray.hpp"
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// #include "xtensor/xfixed.hpp"
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#include "xtensor/xview.hpp"
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namespace xt
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{
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template <class E, std::enable_if_t<!xt::has_rank_t<E, 2>::value, int> = 0>
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inline E sfinae_rank_basic_func(E&& a)
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{
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E b = a;
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b.fill(0);
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return b;
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}
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template <class E, std::enable_if_t<xt::has_rank_t<E, 2>::value, int> = 0>
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inline E sfinae_rank_basic_func(E&& a)
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{
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E b = a;
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b.fill(2);
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return b;
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}
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TEST(sfinae, rank_basic)
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{
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xt::xarray<size_t> a = {{9, 9, 9}, {9, 9, 9}};
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xt::xtensor<size_t, 1> b = {9, 9};
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xt::xtensor<size_t, 2> c = {{9, 9}, {9, 9}};
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// xt::xtensor_fixed<size_t, xt::xshape<2, 2>> d = {{9, 9}, {9, 9}};
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auto v = xt::view(c, 0, xt::all());
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_basic_func(a), 0ul)));
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_basic_func(b), 0ul)));
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_basic_func(c), 2ul)));
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// EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_basic_func(d), 2ul)));
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_basic_func(v), 0ul)));
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}
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template <class E, std::enable_if_t<xt::has_rank_t<E, SIZE_MAX>::value, int> = 0>
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inline E sfinae_rank_func(E&& a)
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{
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E b = a;
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b.fill(0);
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return b;
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}
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template <class E, std::enable_if_t<xt::has_rank_t<E, 1>::value, int> = 0>
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inline E sfinae_rank_func(E&& a)
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{
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E b = a;
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b.fill(1);
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return b;
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}
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template <class E, std::enable_if_t<xt::has_rank_t<E, 2>::value, int> = 0>
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inline E sfinae_rank_func(E&& a)
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{
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E b = a;
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b.fill(2);
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return b;
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}
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TEST(sfinae, rank)
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{
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xt::xarray<size_t> a = {{9, 9, 9}, {9, 9, 9}};
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xt::xtensor<size_t, 1> b = {9, 9};
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xt::xtensor<size_t, 2> c = {{9, 9}, {9, 9}};
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// xt::xtensor_fixed<size_t, xt::xshape<2, 2>> d = {{9, 9}, {9, 9}};
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auto v = xt::view(c, 0, xt::all());
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_func(a), 0ul)));
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_func(b), 1ul)));
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_func(c), 2ul)));
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// EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_func(d), 2ul)));
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EXPECT_TRUE(xt::all(xt::equal(sfinae_rank_func(v), 0ul)));
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}
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}

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