[libcxx-commits] [PATCH] D109475: [libc++] Simplify span specializations

[Joe Loser via Phabricator via libcxx-commits]

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`span` has a partial class template specialization for when the extent
is dynamic. This leads to a lot of repeated code (for type aliases,
constraints on constructors, etc.) which is not ideal. It makes for more
of a maintenance burden as more things are added to `span` such as
current work I'm doing with P1394 <https://reviews.llvm.org/P1394>.

Refactor `span` to be just one class template and handle the few differences
between static and dynamic extents with appropriate constraints and
`if constexpr` where needed. Only store the extent data member when the extent
is dynamic. This ensures no additional storage overhead when the span has a
static extent.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D109475

Files:
  libcxx/include/span
  libcxx/test/std/containers/views/span.cons/span.pass.cpp
  libcxx/test/std/containers/views/span.sub/subspan.fail.cpp

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