[GitHub] [arrow-rs] alamb opened a new issue #199: Implement Debug printing "kernel"

[GitBox <gi...@apache.org>]

alamb opened a new issue #199:
URL: https://github.com/apache/arrow-rs/issues/199


   *Note*: migrated from original JIRA: https://issues.apache.org/jira/browse/ARROW-11882
   
   [~jorgecarleitao] offered a great way to improve the Debug/Display implementations for various Array implementations on https://github.com/apache/arrow/pull/9624#issuecomment-790976766 
   
   The only reason we are implementing to_isize/to_usize on NativeType is because we have a function to represent an array (for Display) that accepts a generic physical type T, and then tries to convert it to a isize depending on a logical type (DataType::Date). However, there is already a Many to one relationship between logical and physical types.
   
   Thus, a solution for this is to have the `Debug` function branch off depending on the (logical) datatype, implementing the custom string representation depending on it, instead of having a loop of native type T and then branching off according to the DataType inside the loop.
   
   I.e. instead of
   
   {code}
   for i in ... {
      match data_type {
            DataType::Date32 => represent array[i] as date
            DataType::Int32 => represent array[i] as int
      }
   }
   {code}
   
   imo we should have
   
   {code}
   match data_type {
        DataType::Date32 => for i in ... {represent array[i] as date}
        DataType::Int32 => for i in ... {represent array[i] as int}
   }
   {code}
   
   i.e. treat the Display as any other "kernel", where behavior is logical, not physical, type-dependent.


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