[jira] [Updated] (ARROW-12804) [C++] Array methods IsNull and IsValid is confused for NullType

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-12804?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

ASF GitHub Bot updated ARROW-12804:
-----------------------------------
    Labels: pull-request-available  (was: )

> [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
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 10m
>  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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