Macro downcast_run_end_index

macro_rules! downcast_run_end_index {
    ($($data_type:expr),+ => ($m:path $(, $args:tt)*), $($p:pat => $fallback:expr $(,)*)*) => { ... };
}

Given one or more expressions evaluating to an integer DataType invokes the provided macro m with the corresponding integer RunEndIndexType, followed by any additional arguments

macro_rules! run_end_size_helper {
  ($t:ty, $o:ty) => {
      std::mem::size_of::<<$t as ArrowPrimitiveType>::Native>() as $o
  };
}

fn run_end_index_size(t: &DataType) -> u8 {
    match t {
        DataType::RunEndEncoded(k, _) => downcast_run_end_index! {
            k.data_type() => (run_end_size_helper, u8),
            _ => unreachable!(),
        },
        _ => u8::MAX,
    }
}

assert_eq!(run_end_index_size(&DataType::RunEndEncoded(Arc::new(Field::new("a", DataType::Int32, false)), Arc::new(Field::new("b", DataType::Utf8, true)))), 4);
assert_eq!(run_end_index_size(&DataType::RunEndEncoded(Arc::new(Field::new("a", DataType::Int64, false)), Arc::new(Field::new("b", DataType::Utf8, true)))), 8);
assert_eq!(run_end_index_size(&DataType::RunEndEncoded(Arc::new(Field::new("a", DataType::Int16, false)), Arc::new(Field::new("b", DataType::Utf8, true)))), 2);