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

In DataFusion we are working on a Merge operator that needs to compare multiple sorted streams of record batches, merge them together, and produce a single sorted output stream (see more context in apache/datafusion#722)

The current interface for comparing arrays in Arrow is getting a DynComparator

Which is a function that you give two indexes and get the result. You effectively have to do

let cmp = build_compare(array1, array2);
... 
if cmp(index1, index2) == OrderingEqual:: {

}

This has two problems for the merge operator:

1. it has to keep track of different comparators for each pairs of arrays that are used
2. (unobviously) by memoizing the comparators it will prevent the underlying array memory from being freed (as each comparator has a reference to the underlying array data)

Describe the solution you'd like

I would ideally like a comparator that does not have the array bound and instead was passed array indexes. Something like

let cmp = build_compare(array1.data_type(), array2.data_type());
... 
if cmp(&array1, index1, &array2, index2) == OrderingEqual:: {

}

We can probably also keep the existing interface

Describe alternatives you've considered
None

Additional context
See discussion with @Dandandan and @e-dard here: apache/datafusion#722 (comment)