first_ok.rs

struct Client {
    members: Vec<Member>,
}

impl Client {
    fn first_ok<F>(&self, callback: F) -> Result<GoodThing, Vec<BadThing>>
    where
        F: Fn(&Member) -> Result<GoodThing, BadThing>
    {
        let mut errors = Vec::with_capacity(self.members.len());

        for member in self.members.iter() {
            let result = callback(member);

            match result {
                Ok(node) => return Ok(node),
                Err(error) => errors.push(error),
            }
        }

        Err(errors)
    }
}

From Arnavion on #rust: https://gist.github.com/anonymous/9f6bd607f42b1b1e8cc7a2dab6e901ae