Notes from 2018-06-Rapperswil LWG review

hcedwar commented 6 years ago

My notes:

mdspan LWG review Daniel Krugler of LWG will help us polish according to LWG expectations

usage of ‘span’ requires reference to C++20 working document need every section to have stable name namespace for the TS – std::experimental::fundamentals_v3 before header synopsis a sentence of overview exposition only in italics k input iterators has used the term ‘domain’ structure domain and codomain as definitions for this clause in italics; email to the library reflector before the pre-meeting mailing for discussion LEWG ok with ‘all’ and ‘all_type’ Destructor does not have noexcept ‘noexecept’ typo typename template layout::mapping templated member functions “OtherElementType” “OtherLayoutType” … assignment conversion operator should not be variadic “DynamicExtent” argument should be “dynamic_extent” All function arguments in the synopsis are named Exposition only members are in italics and each is marked with comment ‘exposition only’ perhaps another exposition name than ‘map’ section breaks within synopsis need to have stable names for the subsections, do not have colons 3.2.1 template arguments stated as requirements “ElementType” shall be … “Extents” shall be a specialization of extents. See the algorithm section for templates as policy requirements; policy requirements appear before the synopsis

3.2.2 Cartesian product times sign need to be math font times, put formula in a separate line Use natural number symbol for extent definition: N_0×N_1 … etc Omit “(at compile time)” and “(at runtime)” Ellipses should not be in code font Marshall – would like an example – would be helpful Function signature must match the synopsis Clause for returns should not cover requires clause, add throws nothing Return for static_extent If rank() <= r then 1 Change all this to “effects equivalent to returns”

3.3 extents Should be before mdpsan Destructor after the constructor … carry Cartesian description to this Synopsis to state what the class is expected to store – the dynamically sized extents Would be simpler to describe with exposition only array member of all extents with note that implementation is expected to only store dynamic extents Template “ExtentsSpecification” name is clearer Default constructor initializes stored dynamic extents as zero See optional or variant or span for constructor argument template description / requirements rank() : returns sizeof…(Extents) rank_dynamic() : returns number of Extents that are equal to dynamic_extent static_extent(int i) : if ith < rank() returns the ith element of Extents… ; otherwise 1 throws nothing constructor needs wording Shall not participate in overload resolution unless sizeof…(dynamic_extents) == rank_dynamic() Wording for constructor with arguments talk about input type Look at tuple equality comparison 3.2.3 Codomain observers Use math style for i^th “dynanic” typo “A span that refers to the codomain” Ill-formed if requires clauses not satisfied Use fold expression for IndexType requirement Wording to prevent “bool” from being used

3.5 Layout Policy Requirements Split into requirements and specific types Use “specialized” not “instantiated” Describe without mentioning basicmdspan 3.5.2 Concept Look at allocator and container for table of valid expressions; e.g., Table 77 Preamble to table also a table that identifies symbols Exposition only layout::mapping<…>::extent ? but very hard to do. Suggestion – layout::mapping::extents() instead of duplicating ? Must include the extents-based constructor 3.2.6 has the wording that belongs here “contiguous” – steal wording from contiguous iterators, remove term ‘span’, no holes in the codomain Bijective is non-normative note Wording for strided – true if and only iff …conditions… ; could lead in with “let” … Wording only refers to extents, layout, mapping is_strided = / see below */

stride( int i ) returns the distance between codomain when incrementing one coordinate in the domain 0 <= i < rank()

3.2.4 Constructors… Default constructor is post_condition Assignment

3.6 Accessor pointer is a contiguous iterator need to say what ‘T’ is An accessor shall meet the requirements … ‘p’ denotes a pointer to a type T

3.5.1 Predefined standard layout policies This is not in wording ! Preamble “These predefined layout policies are provided…” Just show code “row major” and “column major” are notes Look at container requirements and container for requirements and how they satisfy the layout requirements

TARGET post-meeting