interner: minimal working version

trunk_interner/src/lib.rs

@@ -1,14 +1,52 @@
-pub fn add(left: usize, right: usize) -> usize {
-    left + right
+use std::collections::HashMap;
+
+#[derive(Debug, PartialEq)]
+#[repr(transparent)]
+pub struct Symbol(u32);
+
+#[derive(Debug, Default)]
+pub struct Interner {
+    map: HashMap<String, u32>,
+    storage: Vec<String>,
+}
+
+impl Interner {
+    pub fn intern(&mut self, name: &str) -> Symbol {
+        if let Some(&index) = self.map.get(name) {
+            return Symbol(index);
+        }
+
+        let index = self.map.len() as u32;
+
+        self.map.insert(name.to_string(), index);
+        self.storage.push(name.to_string());
+
+        Symbol(index)
+    }
+
+    pub fn get(&self, symbol: Symbol) -> &str {
+        self.storage[symbol.0 as usize].as_str()
+    }
 }
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    use crate::{Interner, Symbol};
+
 
     #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
+    fn it_can_intern_a_string() {
+        let mut interner = Interner::default();
+
+        assert_eq!(interner.intern("Hello, world!"), Symbol(0));
+        assert_eq!(interner.intern("Hello, world!"), Symbol(0));
     }
-}
+
+    #[test]
+    fn it_can_retrieve_an_interned_string() {
+        let mut interner = Interner::default();
+        let symbol = interner.intern("Hello, world!");
+
+        assert_eq!(interner.get(symbol), "Hello, world!");
+    }
+}