Use and Index struct instead of str and String for player id

src/lib.rs

@@ -1,5 +1,8 @@
+use std::borrow::{Borrow, ToOwned};
 use std::cmp::Reverse;
+use std::collections::HashMap;
 use std::f64::consts::{FRAC_1_SQRT_2, FRAC_2_SQRT_PI, SQRT_2};
+use std::hash::Hash;
 
 mod agent;
 #[cfg(feature = "approx")]
@@ -27,19 +30,55 @@ pub const ITERATIONS: usize = 30;
 
 const SQRT_TAU: f64 = 2.5066282746310002;
 
-const N01: Gaussian = Gaussian {
+pub const N01: Gaussian = Gaussian {
     mu: 0.0,
     sigma: 1.0,
 };
-pub(crate) const N00: Gaussian = Gaussian {
+pub const N00: Gaussian = Gaussian {
     mu: 0.0,
     sigma: 0.0,
 };
-pub(crate) const N_INF: Gaussian = Gaussian {
+pub const N_INF: Gaussian = Gaussian {
     mu: 0.0,
     sigma: f64::INFINITY,
 };
 
+#[derive(Copy, Clone, Default, PartialEq, PartialOrd, Eq, Ord, Hash, Debug)]
+pub struct Index(usize);
+
+impl From<usize> for Index {
+    fn from(ix: usize) -> Self {
+        Self(ix)
+    }
+}
+
+pub struct IndexMap<K>(HashMap<K, Index>);
+
+impl<K> IndexMap<K>
+where
+    K: Eq + Hash,
+{
+    pub fn new() -> Self {
+        Self(HashMap::new())
+    }
+
+    pub fn get_or_create<Q: ?Sized>(&mut self, k: &Q) -> Index
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq + ToOwned<Owned = K>,
+    {
+        if let Some(idx) = self.0.get(k) {
+            *idx
+        } else {
+            let idx = Index::from(self.0.len());
+
+            self.0.insert(k.to_owned(), idx);
+
+            idx
+        }
+    }
+}
+
 fn erfc(x: f64) -> f64 {
     let z = x.abs();
     let t = 1.0 / (1.0 + z / 2.0);