feat: allow multiple subscripts

[usamoi]

Ref:

• feat: support vector subscript #329
• chore: consistent slice behavior with Python #352

x[1:2][3:4] in PostgreSQL represents fetching x[0..1, 2..3]. Since vector is always an 1D array we do not support it for the first.

Later we would like to keep consistency with Python haviours. So there are no reason why we do not support multiple subscripts attached to a vector value now. We should implement it for convenience.

[PeterWrighten]

Could I work for this issue?

[usamoi]

Could I work for this issue?

Sure!

[PeterWrighten]

@usamoi Hi, after I tried implementing this feature, and modifying to get multiple subscripts in transform(), I have no idea in modifying sbs_check_subscripts and something else.

I assume it should be implemented with a loop operation, but seems let state = &mut *(*op).d.sbsref.state; is not a list or implemented any memeber function to head next one.

Is there any tutorial, ref or blog to help understand pgrx::pg_sys::SubscriptRef, pgrx::pg_sys::SubscriptRefState and pgrx::pg_sys::SubscriptRoutines?

[usamoi]

I think you need to read PostgreSQL source code. You can read the implementation for arrays.

[PeterWrighten]

I think you need to read PostgreSQL source code. You can read the implementation for arrays.

Thanks!