Create an implementation of span

[JeffGarland]

I have some improvements I'd like to see for std::span which I can share later. To do that we'll need a base implementation of span. Of course I don't have time to do this so I'm looking for a volunteer to help.

[ssam18]

@JeffGarland I’ve been working on it for the past three weeks and will share the repo once it’s ready. I use two GitHub accounts, and the other one is SamareshSingh. I signed up for the Beman project with that account about 2-3 months ago, so the repo will appear under SamareshSingh.

[SamareshSingh]

Hi @JeffGarland, I have put together a base implementation of std::span as requested in this issue.

Repository: https://github.com/SamareshSingh/span

What is implemented

The library lives in the beman::span namespace and follows the Beman project standard (header-only, Apache-2.0 WITH LLVM-exception, CMake install support via beman::span target).

Core features:

• beman::span::dynamic_extent constant (numeric_limits<size_t>::max())
• span<ElementType, Extent = dynamic_extent> class template, full C++20 std::span equivalent
• All constructor overloads: C-array, std::array, pointer + count, pointer pair, generic contiguous range, and cross-span conversions (mutable to const, static to dynamic)
• Observers: size(), size_bytes(), empty()
• Element access: operator[], front(), back(), data()
• Full iterator support: begin/end, rbegin/rend, cbegin/cend, crbegin/crend
• Subviews: first<N>()/first(n), last<N>()/last(n), subspan<Offset,Count>()/subspan(offset, count) — both compile-time and runtime variants
• as_bytes() and as_writable_bytes() free functions
• Deduction guides (C++17)
• constexpr throughout

Tests

44 GoogleTest unit tests covering all of the above, 100% passing. Tests also conditionally compare against std::span when the compiler supports it (__cpp_lib_span).

Build

cmake -B build -S . -DCMAKE_CXX_STANDARD=20
cmake --build build
ctest --test-dir build

Happy to take feedback and make adjustments. Looking forward to hearing what improvements you had in mind on top of this base.

[ssam18]

@JeffGarland - Please find some time to review.

[JeffGarland]

Done. I've added issues directly to the repo including some for the future work. Please move the repo under the beman project banner so it can benefit from the continuous CI improvements and be linked from the website. Fantastic start @SamareshSingh !

I'm closing this issue.

[ssam18]

@JeffGarland - The repo is now under bemanproject/span, as you suggested. PRs are up for all four follow-ups bemanproject/span#10 (at()), bemanproject/span#9 (initializer_list ctor), bemanproject/span#8 (remove_prefix/remove_suffix), bemanproject/span#7 (tuple protocol).
Thanks again for the review!