Closures that Own Their Environment

10 points

Implement make_logger, which returns a closure that formats a message with a fixed prefix, as "{prefix}: {msg}". prefix is a String passed by value into make_logger — the returned closure must capture it by move so it is still valid on every call, long after make_logger itself has returned.

Required signature

pub fn make_logger(prefix: String) -> impl Fn(&str) -> String;

Visible tests

formats_with_prefix

#[test]
fn formats_with_prefix() {
    let log = make_logger("INFO".to_string());
    assert_eq!(log("started"), "INFO: started");
}

Closures that Own Their Environment

Required signature

Visible tests

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