I'm trying to accumulate a HashMap with results from a parallel iterator of json file string data of football matches:

    pub fn build(mut me: Self, raw_data: JsonFilesContentsAllRaw) -> anyhow::Result<Self> {
        const ERROR_FUNC: &'static str = "IMDB::build";
        for (year, files) in raw_data.iter() {
            let hashmaps = files.par_iter().map(|(fname, contents)| {
                let mut hashmap = HashMap::new();
                match Self::turn_file_contents_to_hashmap(contents) {
                    Ok(map) => hashmap = map,
                    Err(err) => {
                        eprintln!(
                            "{ERROR_PREFIX} {ERROR_FUNC}: Error while parsing json file '{year}/{fname}': {err}"
                        );
                    }
                }

                hashmap
            });

            me.flat_hashmap.extend(hashmaps);
        }

        Ok(me)
    }

    fn turn_file_contents_to_hashmap(contents: &str) -> anyhow::Result<HashMap<String, Match>> {
        const ERROR_FUNC: &'static str = "IMDB::turn_file_contents_to_hashmap";
        let data: MatchList = serde_json::from_str(contents).with_context(|| {
            format!("{ERROR_PREFIX} {ERROR_FUNC}: Could not parse json from file contents as a list of matches.")
        })?;

        Ok(HashMap::from_iter(data.matches.into_iter().map(|mch| {
            let mut key = String::new();
            key.push_str(&mch.team1);
            key.push('_');
            key.push_str(&mch.team2);
            key.push('_');
            key.push_str(&mch.date.to_string());

            (key, mch)
        })))
    }

I'm getting this error:

65  |             me.flat_hashmap.extend(hashmaps);
    |                             ------ ^^^^^^^^ `rayon::iter::Map<rayon::collections::btree_map::Iter<'_, std::string::String, std::string::String>, {closure@src/imdb.rs:51:49: 51:68}>` is not an iterator
    |                             |
    |                             required by a bound introduced by this call

Do I need to collect the results in a Vec or something before extending the HashMap?

Thanks

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