use of undeclared type `ParquetWriter`

This seems very simple, but I don't understand ...

use polars::prelude::*;
use std::fs::File;

fn write_df_to_parquet(df: &mut DataFrame) {
    let mut file = File::create("df.parquet").expect("could not create file");

    ParquetWriter::new(&mut file)
    .finish(df)
}

gives use of undeclared type `ParquetWriter` .

Isn't ParquetWriter imported in the use polars::prelude::*; line?

The example given here: https://github.com/pola-rs/polars/blob/51e0e40457d5f2f224df0a4dcf389ced16fbac05/examples/read_csv/src/main.rs

Seems to be accessing ParquetWriter with just that import?

I'm sure I'm missing something silly. Any help or advice would be appreciated.