ARROW-8343: [GLib] Add GArrowRecordBatchIterator

[mrkn]

I'd like to add GArrowRecordBatchIterator as a binding of arrow::RecordBatchIterator class.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-8343

[kou]

+1
I've moved implementations to record-batch.{cpp,h,hpp} to reduce C++ build time. We already do similar things for array implementations.
(Generally, GLib library use one file per class. But we may put multiple classes to one file to reduce build time.)

[mrkn]

I came up with the idea that it can avoid making a vector to introduce GListIterator<T> like arrow::VectorIterator<T>.

@kou How do you think about this?

[kou]

It's a good idea!

[kou]

FYI: I've removed temporary vector in garrow_record_batch_iterator_to_list().

[stevedanomodolor]

I came up with the idea that it can avoid making a vector to introduce GListIterator<T> like arrow::VectorIterator<T>.

@kou How do you think about this?

How do you create a Glist of anything, especially fields. It is not clear how do just looking at the api funtions available. Please I would be gratefull.

What I understand so far is,

To create a GList of fields, your need this funtionn call ->
GList * garrow_struct_data_type_get_fields (GArrowStructDataType *struct_data_type);

which means you have to create a GArrowStructDatatype -> which is dont with this function call

GArrowStructDataType *
garrow_struct_data_type_new (GList *fields);, which also depends on GList, I am a bit confused, how to a funtion depends on another function that depends on it self.

An example how to create Glist would be really appreciated.

I also tried creating each field and when creating the schema, initializing it like this, {filedx, filedy} but it gives an error.

[mrkn]

See https://github.com/apache/arrow/blob/master/c_glib/arrow-glib/schema.cpp#L241-L247, this is a typical pattern to make a GList from scratch.

By the way, please do not ask unrelated things to this pull-request here.
You can ask anything about Apache Arrow in the mailing list.
http://mail-archives.apache.org/mod_mbox/arrow-dev/

[mrkn]

@kou I noticed GListIterator is not usable for implementing GArrowRecordBatchIterator because it is a binding of single arrow::RecordBatchIterator instead of a list of GArrowRecordBatch.

I postponed to introduce GListIterator until we actually need it.

[kou]

OK. Then I'll merge this pull request.

[mrkn]

@kou I noticed again that GListIterator can be used just only for garrow_record_batch_iterator_new. I was confused.

[kou]

OK. We can work on it as a follow-up pull request.

[mrkn]

OK!