any_hash.rs

use std::hash::Hash;
use std::cmp::Eq;
use std::any::{Any, TypeId};
use std::collections::HashMap;

pub struct AnyMap<K>(HashMap<(TypeId, K), Box<dyn Any>>);

impl<K: Hash + Eq> AnyMap<K> {
    pub fn new() -> Self {
        Self(HashMap::new())
    }

    pub fn insert<V: Any>(&mut self, key: K, val: V) {
        self.0.insert((TypeId::of::<V>(), key), Box::new(val));
    }

    pub fn get<T: Any>(&self, key: K) -> Option<&T> {
        self.0.get(&(TypeId::of::<T>(), key))?.downcast_ref::<T>()
    }

    pub fn get_mut<T: Any>(&mut self, key: K) -> Option<&mut T> {
        self.0.get_mut(&(TypeId::of::<T>(), key))?.downcast_mut::<T>()
    }
}

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

    #[test]
    fn can_store_anything() {
        let pi: f64 = 3.142;
        let hello: String = "Hello World".to_owned();
        let mut storage = AnyMap::new();
        storage.insert("pi", pi);
        storage.insert("hello", hello);

        assert_eq!(
            storage.get::<f64>("pi").unwrap(),
            &3.142
        );

        assert_eq!(
            storage.get::<String>("hello").unwrap(),
            &"Hello World".to_owned()
        );

        storage.get_mut::<String>("hello").unwrap().push_str("!!!");

        assert_eq!(
            storage.get::<String>("hello").unwrap(),
            &"Hello World!!!".to_owned()
        );
    }
}