foo.rs

struct Foo {
    data: Vec<f64>,
}

trait FileData {
    fn new(raw_data: &[u8]) -> Self;
    fn get_data(&self) -> &Vec<f64> {
        &self.data
    }
    fn default_method(&self) -> f64 {
        self.get_data().first() * self.get_data().last()
    }
}

impl FileData for Foo {
    fn new(raw_data: &[u8]) -> Self {
        // something
    }
}