Support constant array.

[liurenjie1024]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

A constant array would be useful for improving performance, see apache/iceberg-rust#295 (comment)

Describe the solution you'd like

Allow constructing constant array.

Describe alternatives you've considered

Additional context

[tustvold]

Is https://docs.rs/arrow-array/latest/arrow_array/struct.Scalar.html perhaps what you are looking for?

[liurenjie1024]

Is https://docs.rs/arrow-array/latest/arrow_array/struct.Scalar.html perhaps what you are looking for?

Not quite same. Here is the case, when we want to convert iceberg predicate to ArrowPredicateFn, say a < 1, for some reason here a is a constant, e.g. NULL, we can always return true. But ArrowPredicateFn requires to return an BooleanArray.

[mapleFU]

https://arrow.apache.org/docs/format/Columnar.html

Seems arrow doesn't have an constant array ( But array with type "Null" is similiar to that), maybe send this to maillist is prefered?

[liurenjie1024]

https://arrow.apache.org/docs/format/Columnar.html

Seems arrow doesn't have an constant array ( But array with type "Null" is similiar to that), maybe send this to maillist is prefered?

Cool, I will send a mail to dev list.

[tustvold]

Constant propogation is something I'd expect to be handled by a query optimizer, perhaps in conjunction with range analysis. FWIW Datafusion is already capable of this

[liurenjie1024]

Yes, it possible to be handled by expression rewrite.