[jira] [Commented] (ARROW-47) [C++] Consider adding a scalar type object model

["Antoine Pitrou (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-47?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16719027#comment-16719027 ] 

Antoine Pitrou commented on ARROW-47:
-------------------------------------

I think there are several dimensions in the design space that should be explored.

* Should scalars be backed by an ArrayData, or be standalone (or possibly one or the other)? Backing by an ArrayData allows cheap passing of binary values for example (like a std::string_view), while standalone values would be more expensive (some types will come with their owned piece of memory like a std::string). But standalone values are also more flexible in usage (you don't need a separate ArrayData that you must remember to keep alive...).

* Can scalars have disjoint types, or is a common base class desired? Or perhaps even a single union type, possible a {{variant}}? Those different solutions have different costs, and also different usage models.


> [C++] Consider adding a scalar type object model
> ------------------------------------------------
>
>                 Key: ARROW-47
>                 URL: https://issues.apache.org/jira/browse/ARROW-47
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: C++
>            Reporter: Wes McKinney
>            Assignee: Uwe L. Korn
>            Priority: Major
>              Labels: Analytics
>             Fix For: 0.13.0
>
>
> Just did this on the Python side. In later analytics routines, passing in scalar values (example: Array + Scalar) requires some kind of container. Some systems, like the R language, solve this problem with length-1 arrays, but we should do some analysis of use cases and figure out what will work best for Arrow.



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