[C++] Array methods IsNull and IsValid is confused for NullType

[asfimport]

I'm not sure if this is a bug or by design.

Array's method IsNull() and IsValid() is implemented as follows:

/// \brief Return true if value at index is null. Does not boundscheck
bool IsNull(int64_t i) const {
  return null_bitmap_data_ != NULLPTR &&
         !BitUtil::GetBit(null_bitmap_data_, i + data_->offset);
}

/// \brief Return true if value at index is valid (not null). Does not
/// boundscheck
bool IsValid(int64_t i) const {
  return null_bitmap_data_ == NULLPTR ||
         BitUtil::GetBit(null_bitmap_data_, i + data_->offset);
}

According to the doc, "Arrays having a 0 null count may choose to not allocate the null bitmap". But a null type array doesn't have a null bitmap. So for a null type array, IsNull() always returns false, IsValid() always returns true.

If this is by design, maybe additional comments and docs should be added.

Reporter: Chenxi Li / @Crystrix
Assignee: Nate Clark / @n3world

Related issues:

• [C++] NullArray::IsNull always returns false and NullArray::IsValid always returns true (is duplicated by)

PRs and other links:

• GitHub Pull Request #10756

_{Note: This issue was originally created as ARROW-12804. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 10756
#10756