use std::ops::{Index, IndexMut};

pub struct Id<T> {
    idx: usize,
    _pd: std::marker::PhantomData<T>,
}

pub struct IdVec<T> {
    vec: Vec<T>,
}

impl<T> IdVec<T> {
    pub fn add(&mut self, val: T) -> Id<T> {
        let id = Id {
            idx: self.vec.len(),
            _pd: Default::default(),
        };
        self.vec.push(val);
        id
    }
}

impl<T> Index<Id<T>> for IdVec<T> {
    type Output = T;

    fn index(&self, index: Id<T>) -> &Self::Output {
        &self.vec[index.idx]
    }
}

impl<T> IndexMut<Id<T>> for IdVec<T> {
    fn index_mut(&mut self, index: Id<T>) -> &mut Self::Output {
        &mut self.vec[index.idx]
    }
}

impl<T> Default for IdVec<T> {
    fn default() -> Self {
        Self {
            vec: Default::default(),
        }
    }
}

impl<T> Clone for Id<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T> Copy for Id<T> {}