GH-44795: [C++] Use arrow::util::span<T> on BooleanBuilder APIs instead of std::vector<T>&

[raulcd]

Rationale for this change

arrow::util::span (a backport of C++20 std::span) is more generally applicable than std::vector, so any public API currently accepting a vector const-ref argument should instead accept a span argument.

What changes are included in this PR?

BooleanBuilder accepts arrow::util::span instead of std::vector on its API

Are these changes tested?

Via CI

Are there any user-facing changes?

Yes, from std::vector& to arrow::util::span.

• GitHub Issue: [C++] APIs taking a const vector<T>& argument should instead take a span<const T> #44795

[raulcd]

I created a second PR to investigate further what is going on but it seems like it's not able to convert from std::vector<bool>& to arrow::util::span<bool> so there might be an issue on our implementation of arrow::util::span

[raulcd]

This is the error I get:

code/arrow/cpp/src/arrow/array/builder_primitive.h:474:46:
        note:   no known conversion for argument 1 from ‘std::vector<bool>’ to ‘arrow::util::span<bool>’
  474 |   Status AppendValues(const util::span<bool> values);
      |                       ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~

when trying to convert on this test:

  BooleanBuilder builder;
  std::vector<bool> zeros(length);
  ASSERT_OK(builder.AppendValues(zeros));

@bkietz my C++ skills aren't great but shouldn't we be able to use std::vector<bool> for our utill::span<bool>?

[pitrou]

@raulcd That's because std::vector<bool> is special, so you cannot replace it with a span like that. Sorry!

[pitrou]

So, const std::vector<T>& should be replaced with util::span<const T>, not const util::span<T> (because a span's constness doesn't propagate to the elements it points to, unlike vector).

[pitrou]

Can just say "a span of bytes" IMHO.