presto-orc/src/main/java/io/prestosql/orc/reader/ColumnReaders.java/ColumnReaders/createColumnReader
class ColumnReaders:    public static ColumnReader createColumnReader(Type type, OrcColumn column, AggregatedMemoryContext systemMemoryContext, OrcBlockFactory blockFactory)
            throws OrcCorruptionException
    {
        switch (column.getColumnType()) {
            case BOOLEAN:
                return new BooleanColumnReader(type, column, systemMemoryContext.newLocalMemoryContext(ColumnReaders.class.getSimpleName()));
            case BYTE:
                return new ByteColumnReader(type, column, systemMemoryContext.newLocalMemoryContext(ColumnReaders.class.getSimpleName()));
            case SHORT:
            case INT:
            case LONG:
            case DATE:
                return new LongColumnReader(type, column, systemMemoryContext.newLocalMemoryContext(ColumnReaders.class.getSimpleName()));
            case FLOAT:
                return new FloatColumnReader(type, column, systemMemoryContext.newLocalMemoryContext(ColumnReaders.class.getSimpleName()));
            case DOUBLE:
                return new DoubleColumnReader(type, column, systemMemoryContext.newLocalMemoryContext(ColumnReaders.class.getSimpleName()));
            case BINARY:
            case STRING:
            case VARCHAR:
            case CHAR:
                return new SliceColumnReader(type, column, systemMemoryContext);
            case TIMESTAMP:
                return new TimestampColumnReader(type, column, systemMemoryContext.newLocalMemoryContext(ColumnReaders.class.getSimpleName()));
            case LIST:
                return new ListColumnReader(type, column, systemMemoryContext, blockFactory);
            case STRUCT:
                return new StructColumnReader(type, column, systemMemoryContext, blockFactory);
            case MAP:
                return new MapColumnReader(type, column, systemMemoryContext, blockFactory);
            case DECIMAL:
                return new DecimalColumnReader(type, column, systemMemoryContext.newLocalMemoryContext(ColumnReaders.class.getSimpleName()));
            case UNION:
            default:
                throw new IllegalArgumentException("Unsupported type: " + column.getColumnType());
        }
    }