use std::collections::HashSet;
use std::hash::{Hash, Hasher};
use std::collections::hash_map::DefaultHasher;

struct HashOnlySet {
    set: HashSet<u64>,
}

impl HashOnlySet {
    fn new() -> HashOnlySet {
        HashOnlySet { set: HashSet::new() }
    }

    fn insert<T: Hash>(&mut self, item: &T) -> bool {
        let hash = Self::hash_item(item);
        self.set.insert(hash)
    }

    fn contains<T: Hash>(&self, item: &T) -> bool {
        let hash = Self::hash_item(item);
        self.set.contains(&hash)
    }

    fn hash_item<T: Hash>(item: &T) -> u64 {
        let mut hasher = DefaultHasher::new();
        item.hash(&mut hasher);
        hasher.finish()
    }
}

fn main() {
    let mut set = HashOnlySet::new();
    set.insert(&"Hello, world!");
    println!("Contains 'Hello, world!': {}", set.contains(&"Hello, world!"));
    println!("Contains 'Goodbye, world!': {}", set.contains(&"Goodbye, world!"));
}