[mdspan.sub.map.sliceable] (original) (raw)

23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.7 submdspan [mdspan.sub]

23.7.3.7.7 Specializations of submdspan_mapping [mdspan.sub.map]

23.7.3.7.7.1 Sliceable layout mapping requirements [mdspan.sub.map.sliceable]

Let:

• M denote a layout mapping class;
• IT denote M​::​extent_type​::​index_type;
• m denote a value of type (possibly const) M;
• M_rank be equal to M​::​extent_type​::​rank();
• valid_slices denote a pack of (possibly const) objects for which sizeof...(valid_slices) == M_rank is true and, for each rank index i of m.extents(),valid_slices...[i] is a valid submdspan slice for the extent of m.extents();
• invalid_slices denote a pack of objects for which sizeof...(invalid_slices) == M_rank is true and there exists an integer k such that the cv-unqualified type of invalid_slices...[k] is none of the following:
  • IT,
  • full_extent_t,
  • a specialization of constant_wrapper, or
  • a specialization of strided_slice.

For the purpose of this section, the meaning of submdspan_mapping is established as if by performing argument-dependent lookup only ([basic.lookup.argdep]).

A type M meets the sliceable layout mapping requirements if

• M meets the layout mapping requirements ([mdspan.layout.policy.reqmts]),
• the expression submdspan_mapping(m, invalid_slices...) is ill-formed, and
• the following expression is well-formed and has the specified semantics:submdspan_mapping(m, valid_slices...)

Result: A type SMR that is a specialization of type submdspan_mapping_result for some type SM such that

• SM meets the layout mapping requirements ([mdspan.layout.policy.reqmts]),
• SM​::​extents_type is a specialization of extents,
• SM​::​extents_type​::​rank() equals_MAP_RANK_(valid_slices, M_rank), and
• SM​::​extents_type​::​index_type denotes IT.

Returns: An object smr of type SMR such that

• smr.mapping.extents() == submdspan_extents(m.extents(), valid_slices...) is true;
  and
• for each integer pack i which is a multidimensional index in smr.mapping.extents(),
  smr.mapping(i...) + smr.offset == m(j) is true, where j is an integer pack such that
  • sizeof...(j) is equal to M_rank; and
  • for each rank index ρ of m.extents(),j...[ρ] is equal to the sum of
    * the lower bound of the submdspan slice range of valid_slices...[ρ] for extent ρ of m.extents(), and
    * zero if the type of valid_slices...[ρ] is a collapsing slice type,i...[MAP_RANK(valid_slices,ρ)] otherwise.

template<class LayoutMapping> concept [_sliceable-mapping_](#concept:sliceable-mapping "23.7.3.7.7.1 Sliceable layout mapping requirements [mdspan.sub.map.sliceable]") = _see below_;

Let lm be an object of type LayoutMappingand let fe denote a pack of objects of type full_extent_tfor which sizeof...(fe) == LayoutMapping​::​extents_type​::​rank() is true.

A type LayoutMapping satisfies sliceable-mapping if

• the expression submdspan_mapping(m, fe...) is well-formed when treated as an unevaluated operand, and
• the type of that expression is a specialization ofsubmdspan_mapping_result.

A type LayoutMapping models sliceable-mappingif LayoutMapping meets the sliceable layout mapping requirements.