[C++] AppendScalar implementation uses polymorphism

[pitrou]

Describe the enhancement requested

The ArrayBuilder::AppendScalar implementation is currently very odd:

• the ArrayBuilder hierarchy uses polymorphism (i.e. virtual methods) to handle type-specific operations
• but ArrayBuilder::AppendScalar is implemented entirely in the base class using a visitor, putting type-specific knowledge in the base class definition
• but ArrayBuilder::AppendScalar is also a virtual method overriden in dictionary and run-end-encoded builders
• furthermore, the visitor in the base class definition of ArrayBuilder::AppendScalar dispatched on the scalar's data type, instead of the builder's data type

We should refactor the AppendScalar implementation to be entirely polymorphic and remove any trace of type-specific implementations in the base class (ArrayBuilder::AppendScalar would probably become a pure virtual method).

This would also help in cases like #50584

Component(s)

C++

[SHAURYASAXENA2024]

Hi! I'd like to work on this issue if it's still available. Please let me know if someone is already working on it.

[pitrou]

@SHAURYASAXENA2024 I think you haven't contributed before? This issue is probably too complex, please look for issues with the "good first issue" label.

[SHAURYASAXENA2024]

Thank you very much for your advice! Yes, you are correct, this is my first time contributing to Apache Arrow. First, I will become acquainted with the code base and the contribution process.

[VedantRalekar]

Hi, anyone working on this issue ?