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std::strided_slice(3)	      C++ Standard Libary	 std::strided_slice(3)

NAME
       std::strided_slice - std::strided_slice

Synopsis
	  Defined in header <mdspan>
	  template<  class  OffsetType,	 class	ExtentType, class StrideType >
       (since C++26)
	  struct strided_slice;

	  An instance of every specialization  of  strided_slice  is  a	 slice
       specifier used in
	  std::submdspan  to  select a subset of elements using	a set of regu-
       larly spaced
	  indices at a specified dimension in std::mdspan. It  provides	 three
       values: the
	  offset index,	the extent, and	the stride.

	  Given	 that  stride is greater than zero, let	N be the number	of se-
       lected indices
	  which	is determined by 1 + (extent  -	 1)  /	stride	if  extent  is
       nonzero,	otherwise 0.
	  The  indices	are selected from half-open interval [offset, offset +
       extent).	Hence,
	  the selected indices are offset, ...,	offset + (N - 1) * stride.

	  This class template has no base classes or  declared	members	 other
       than those shown
	  below.

Template parameters
	  OffsetType			   the	types  of  offset, extent, and
       stride,
	  ExtentType	       -	  respectively.
	  StrideType

Type requirements
	  -
	  All template parameters must be unsigned or signed integer types  or
       must satisfy
	  integral-constant-like

	  The program is ill-formed if the type	requirement is not satisfied.

Member types
	  Member type Definition
	  offset_type OffsetType
	  extent_type ExtentType
	  stride_type StrideType

	  Data members

	  Member name Definition
	  offset      a	starting index of type offset_type
		      (public member object)
		      a	 value of type extent_type added to offset used	to de-
       fine the	upper
	  extent      bound of indices
		      (public member object)
		      an increment value of type stride_type which is  equiva-
       lent to the
	  stride      distance between two indices
		      (public member object)

	  All  these members are declared with [[no_unique_address]] attribute
       and have	default
	  member initializers where each data member is	value initialized.

Notes
	  Every	specialization of strided_slice	is an  aggregate  class	 which
       allows aggregate
	  initialization (including designated initialization) of data members
       (for instance,
	  std::strided_slice { .offset = 2, .extent = 10, .stride = 3 }).

	  The slice specification of strided_slice takes advantage of the data
       member extent,
	  as  opposed  to  other slice specifications that use end to indicate
       the upper bound
	  value. This is because it can	directly generate a static extent  for
       subview of
	  std::mdspan if both extent and stride	are of types that satisfy
	  integral-constant-like.  This	 enables  efficient extraction of sub-
       views with static
	  extents by mixing compile time values	with a runtime value  of  off-
       set.

Example
       // Run this code

	#include <mdspan>
	#include <print>

	template  <typename View, typename O = int, typename E = int, typename
       S = int>
	    requires (View::extents_type::rank() == 1)
	void print_sliced_view(View v, std::strided_slice<O, E,	S> s)
	{
	    using index_type = View::index_type;
	    auto subview = std::submdspan(v, s);
	    const auto&	submap = subview.mapping();

	    std::print("[");
	    bool uses_comma = false;
	    for	(index_type i =	0; i < subview.extent(0); ++i)
	    {
		if (uses_comma)
		    std::print(", ");
		std::print("{}", subview[i]);
		uses_comma = true;
	    }
	    uses_comma = false;
	    std::print("] extracted from indices [");
	    for	(index_type i =	0; i < subview.extent(0); ++i)
	    {
		if (uses_comma)
		    std::print(", ");
		std::print("{}", submap(i) + s.offset);
		uses_comma = true;
	    }
	    std::println("]");
	}

	int main()
	{
	    static constexpr char letters [] {
		'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',	'I', 'J',
		'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',	'S', 'T',
		'U', 'V', 'W', 'X', 'Y', 'Z'
	    };
	    constexpr std::mdspan md (letters, 26);
	    print_sliced_view(md, {.offset = 0,	.extent	= 10, .stride =	1});
	    print_sliced_view(md, {.offset = 2,	.extent	= 10, .stride =	1});
	    print_sliced_view(md, {.offset = 0,	.extent	= 5,  .stride =	1});
	    print_sliced_view(md, {.offset = 2,	.extent	= 5,  .stride =	1});
	    print_sliced_view(md, {.offset = 0,	.extent	= 10, .stride =	2});
	    print_sliced_view(md, {.offset = 2,	.extent	= 10, .stride =	3});
	    print_sliced_view(md, {.offset = 0,	.extent	= 15, .stride =	5});
	    print_sliced_view(md, {.offset = 6,	.extent	= 15, .stride =	5});
	}

Output:
	[A, B, C, D, E,	F, G, H, I, J] extracted from indices [0, 1, 2,	3,  4,
       5, 6, 7,	8, 9]
	[C,  D,	E, F, G, H, I, J, K, L]	extracted from indices [2, 3, 4, 5, 6,
       7, 8, 9,	10, 11]
	[A, B, C, D, E]	extracted from indices [0, 1, 2, 3, 4]
	[C, D, E, F, G]	extracted from indices [2, 3, 4, 5, 6]
	[A, C, E, G, I]	extracted from indices [0, 2, 4, 6, 8]
	[C, F, I, L] extracted from indices [2,	5, 8, 11]
	[A, F, K] extracted from indices [0, 5,	10]
	[G, L, Q] extracted from indices [6, 11, 16]

See also
	  slice	    BLAS-like slice of a  valarray:  starting  index,  length,
       stride
		    (class)
	  submdspan returns a view of a	subset of an existing mdspan
	  (C++26)   (function template)

http://cppreference.com		  2024.06.10		 std::strided_slice(3)

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