Function dictionary_cast 

pub(crate) fn dictionary_cast<K: ArrowDictionaryKeyType>(
    array: &dyn Array,
    to_type: &DataType,
    cast_options: &CastOptions<'_>,
) -> Result<ArrayRef, ArrowError>

Attempts to cast an ArrayDictionary with index type K into to_type for supported types.

K is the key type