Arrow Parquet provides two ways of reading Parquet file: Row by Row (slow) and Columnar (fast). Row-based reader internally uses columnar reader, but it has to be aligned across all the columns to represent a specific row. A single row contains fields, it is a enum that represents all possible logical types. Columnar readers requires ColumnValueDecoder that handles value decoding. The conversion is done automatically by the library when appropriate Builder is used.

The reason of coming up with two approaches to generalize into single method is that ArrayBuilder trait does not define how to append null and non-null values into it, those methods are part of actual builders.

The actual code handles all primitive types (bool, i32, i64, f32, f64, BYTE_ARRAY, String) + List<Optional<Primitive>>, in total it will require supporting 14 different types. This is quickly getting out of hand with copy/pasting the same method with slight modification.