Reference mdspan implementation

The ISO-C++ proposal P0009 will add support for non-owning multi-dimensional array references to the C++ standard library. This repository aims to provide a production-quality implementation of the proposal as written (with a few caveats, see below) in preparation for the addition of mdspan to the standard. Please feel free to use this, file bugs when it breaks, and let us know how it works for you :-)

Try it out on Godbolt{: .btn }

Using mdspan

A tutorial-style introduction to the basic usage of mdspan is provided on the project wiki. More advanced tutorials to come.

Features in Addition To C++ Standard

• C++17 backport (e.g., concepts not required)
• C++14 backport (e.g., fold expressions not required)
  • Compile times of this backport will be substantially slower than the C++17 version
• Macros to enable, e.g., __device__ marking of all functions for CUDA compatibility

Building and Installation

This implementation is header-only, with compiler features detected using feature test macros, so you can just use it directly with no building or installation. If you would like to run the included tests or benchmarks, you'll need CMake.

Running tests

TODO write this

Running benchmarks

TODO write this

Caveats

This implementation is fully conforming with a few exceptions (most of which are extensions):

C++20

• implements operator() not operator[]
  • note you can control which operator is available with defining MDSPAN_USE_BRACKET_OPERATOR=[0,1] and MDSPAN_USE_PAREN_OPERATOR=[0,1] irrespective of whether multi dimensional subscript support is detected.

C++17 and C++14

• the conditional explicit markup is missing, making certain constructors implicit
  • most notably you can implicitly convert from dynamic extent to static extent, which you can't in C++20 mode

C++14

• deduction guides don't exist

Acknowledgements

This work was undertaken as part of the Kokkos project at Sandia National Laboratories. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidary of Honeywell International Inc., for the U. S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.