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https://issues.apache.org/jira/browse/ARROW-12804?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Antoine Pitrou reassigned ARROW-12804:
--------------------------------------
Assignee: Nate Clark
> [C++] Array methods IsNull and IsValid is confused for NullType
> ---------------------------------------------------------------
>
> Key: ARROW-12804
> URL: https://issues.apache.org/jira/browse/ARROW-12804
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++
> Affects Versions: 4.0.0
> Reporter: Chenxi Li
> Assignee: Nate Clark
> Priority: Major
> Labels: pull-request-available
> Fix For: 5.0.0
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> I'm not sure if this is a bug or by design.
> Array's method {{IsNull()}} and {{IsValid()}} is implemented as follows:
> {code:c++}
> /// \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);
> }
> {code}
> 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.
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