[Solved] Function taking slice of objects as well as slice of references to objects

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3

If you want to skip the cloning, you could use the AsRef trait (playground).

impl AsRef<Age> for Age {
    fn as_ref(&self) -> &Age {
        self
    }
}

fn sum_ages_2<A: AsRef<Age>>(ages: &[A]) -> u32 {
    ages.iter().fold(0, |acc, e| acc + e.as_ref().age)
}

fn process_ages(ages: &[Option<Age>]) -> u32 {
    let somes: Vec<&Age> = ages.iter()
        .filter(|x| x.is_some())
        .map(|x| x.as_ref().unwrap())
        .collect();

    sum_ages_2(&somes)
}

fn main() {
    let ages: Vec<Option<Age>> = vec![Some(Age { age: 1 }), None, Some(Age { age: 2 })];

    assert_eq!(process_ages(&ages), 3);

    let moar_ages = vec![Age { age: 1 }, Age { age: 2 }];
    assert_eq!(sum_ages_2(&moar_ages), 3);
}

This works because you are effectively "abstracting" over whether you have something or a reference to it. In this case, as long as you can get a reference to the thing then that's all we care about.