Tensor Rank¶
Rank overload¶
All xtensor’s classes have a member rank
that can be used
to overload based on rank using SFINAE.
Consider the following example:
template <class E, std::enable_if_t<!xt::has_rank_t<E, 2>::value, int> = 0>
inline E foo(E&& a)
{
... // act on object of flexible rank, or fixed rank != 2
}
template <class E, std::enable_if_t<xt::has_rank_t<E, 2>::value, int> = 0>
inline E foo(E&& a)
{
... // act on object of fixed rank == 2
}
int main()
{
xt::xarray<size_t> a = {{9, 9}, {9, 9}};
xt::xtensor<size_t, 1> b = {9, 9};
xt::xtensor<size_t, 2> c = {{9, 9}, {9, 9}};
foo(a); // flexible rank -> first overload
foo(b); // fixed rank == 2 -> first overload
foo(c); // fixed rank == 2 -> second overload
return 0;
}
Note
If one wants to test for more than a single value for rank
,
one can use the default value SIZE_MAX
used for flexible rank objects.
For example, one could have the following overloads:
// flexible rank
template <class E, std::enable_if_t<!xt::has_fixed_rank_t<E>::value, int> = 0>
inline E foo(E&& a);
// fixed rank == 1
template <class E, std::enable_if_t<xt::has_rank_t<E, 1>::value, int> = 0>
inline E foo(E&& a);
// fixed rank == 2
template <class E, std::enable_if_t<xt::has_rank_t<E, 2>::value, int> = 0>
inline E foo(E&& a);
Note that fixed ranks other than 1 and 2 will raise a compiler error.
Of course, if one wants a more limited scope, one could also do the following:
// flexible rank
inline void foo(xt::xarray<double>& a);
// fixed rank == 1
inline void foo(xt::xtensor<double,1>& a);
// fixed rank == 2
inline void foo(xt::xtensor<double,2>& a);
Rank as member¶
If you want to use the rank as a member of your own class you can use xt::get_rank<E>
.
Consider the following example:
template <class T>
struct Foo
{
static const size_t rank = xt::get_rank<T>::value;
static size_t value()
{
return rank;
}
};
int main()
{
xt::xtensor<double, 1> A = xt::zeros<double>({2});
xt::xtensor<double, 2> B = xt::zeros<double>({2, 2});
xt::xarray<double> C = xt::zeros<double>({2, 2});
std::cout << Foo<decltype(A)>::value() << std::endl;
std::cout << Foo<decltype(B)>::value() << std::endl;
std::cout << Foo<decltype(C)>::value() << std::endl;
return 0;
}