GH-48490: [GLib][Ruby] Add GArrowMakeStructOptions

[stenlarsson]

Rationale for this change

The MakeStructOptions class is not available in GLib/Ruby, and it is used together with the make_struct compute function.

What changes are included in this PR?

This adds the MakeStructOptions class to GLib.

Are these changes tested?

Yes, with Ruby unit tests.

Are there any user-facing changes?

Yes, a new class.

• GitHub Issue: #48490

[github-actions[bot]]

:warning: GitHub issue #48490 has been automatically assigned in GitHub to PR creator.

[stenlarsson]

The class is missing the field_nullability and field_metadata properties because I ran into limitations of the gobject-introspection gem, e.g.: NotImplementedError: TODO: GIArgument(GList)[ghash] -> Ruby. I couldn't figure out what types the properties should have for it to work.

[kou]

Could you push the code that raises NotImplementedError: TODO: GIArgument(GList)[ghash] -> Ruby? I'll improve gobject-introspection gem for the case.

[stenlarsson]

I pushed some code. I couldn't figure out what types the properties should have, so I added getters and setters instead, but it doesn't work because of the limitations in gobject-introspection. I'm sure there are more problems with this code, since I can't test it. Perhaps there is a better way to do it?

[kou]

Thanks. I understand this situation and I also consider API.

How about the following API?

GArrowMakeStructOptions *
garrow_make_struct_options_new(void);
void
garrow_make_struct_options_add_field(GArrowMakeStructOptions *options, const char *name, gboolean nullability, GHashTable *metadata);

// no getter or
const char *
garrow_make_struct_options_get_field_name(GArrowMakeStructOptions *options, gsize i);
gboolean
garrow_make_struct_options_get_field_nullability(GArrowMakeStructOptions *options, gsize i);
GHashTable *
garrow_make_struct_options_get_field_metadta(GArrowMakeStructOptions *options, gsize i);

GArrowMakeStructOptions *options = garrow_make_struct_options_new();
garrow_make_struct_options_add_field(options, name1, nullability1, metadata1);
garrow_make_struct_options_add_field(options, name2, nullability2, metadata2);
...

[stenlarsson]

I implemented your suggested API. I have some code in my own project that automatically generates Ruby code from the function doc, and it wouldn't work with this API. Still, I guess it is the best we can do.

[stenlarsson]

Wow! How do you implement it?

The project is not open source, but I extracted the relevant parts and put together an example: https://github.com/stenlarsson/arrow-plan/blob/main/test.rb

It provides syntax sugar to make it easier to create and execute Acero plans. Since we generate code for the compute functions, your IDE can show you which functions exist, and what arguments and options they take. Symbols are used to reference fields, and some common Ruby types are automatically wrapped as well. In my opinion it makes it much easier to read the code.

However, this only works if the options classes uses properties. If they use any other API, it becomes inconvenient.