deref.rs

use std::ops::Deref;

pub struct Foo;
impl Foo {
    pub fn f(&self) -> &str { "Foo" }
}

pub struct BoxA<T>(T);
impl<T> Deref for BoxA<T> {
    type Target = T;
    fn deref(&self) -> &Self::Target { &self.0 }
}
impl<T> BoxA<T> {
    pub fn f(&self) -> &str { "BoxA" }
}

pub struct BoxB<T>(T);
impl<T> Deref for BoxB<T> {
    type Target = T;
    fn deref(&self) -> &Self::Target { &self.0 }
}
impl<T> BoxB<T> {
    pub fn f(&self) -> &str { "BoxB" }
}

pub struct BoxC<T>(T);
impl<T> Deref for BoxC<T> {
    type Target = T;
    fn deref(&self) -> &Self::Target { &self.0 }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn deref() {
        let v = BoxB(BoxA(Foo));
        assert_eq!(v.f(), "BoxB");
        assert_eq!((*v).f(), "BoxA");
        assert_eq!((*(*v)).f(), "Foo");

        let u = BoxC(BoxA(Foo));
        assert_eq!(u.f(), "BoxA");
    }
}