Static string hash map optimisations

playground.rs

use std::cell::RefCell;
use std::collections::HashMap;
use std::hash::{ Hash, SipHasher, Hasher };

thread_local!(static SYMBOL_HASHES: RefCell<HashMap<(*const u8, usize), u64>> = RefCell::new(HashMap::new()));

struct StaticSymbol {
    string: &'static str,
    hash: u64,
}

impl StaticSymbol {
    fn new(string: &'static str) -> StaticSymbol {
        let hash = SYMBOL_HASHES.with(|map| {
            *map.borrow_mut().entry((string.as_ptr(), string.len()))
                .or_insert_with(|| {
                    let mut hasher = SipHasher::new();
                    string.hash(&mut hasher);
                    hasher.finish()
                })
        });
        StaticSymbol {
            string: string,
            hash: hash
        }
    }
}

impl PartialEq for StaticSymbol {
    fn eq(&self, other: &StaticSymbol) -> bool {
        (self.string.as_ptr() == other.string.as_ptr()
            && self.string.len() == other.string.len())
        || self.string == other.string
    }
}

impl Eq for StaticSymbol {

}

impl Hash for StaticSymbol {
    fn hash<H: Hasher>(&self, state: &mut H) {
        state.write_u64(self.hash);
    }
}

fn main() {
    let s = StaticSymbol::new("foo");
    println!("Hello, world!");
}