fix: return error instead of panicking on out-of-bounds categorical index

src/parameter.rs

@@ -467,7 +467,11 @@ impl<T: Clone + Debug> Parameter for CategoricalParam<T> {
 
     fn cast_param_value(&self, param_value: &ParamValue) -> Result<T> {
         match param_value {
-            ParamValue::Categorical(index) => Ok(self.choices[*index].clone()),
+            ParamValue::Categorical(index) => self
+                .choices
+                .get(*index)
+                .cloned()
+                .ok_or(Error::Internal("categorical index out of bounds")),
             _ => Err(Error::Internal(
                 "Categorical distribution should return Categorical value",
             )),
@@ -708,7 +712,8 @@ impl<T: Categorical + Debug> Parameter for EnumParam<T> {
 
     fn cast_param_value(&self, param_value: &ParamValue) -> Result<T> {
         match param_value {
-            ParamValue::Categorical(index) => Ok(T::from_index(*index)),
+            ParamValue::Categorical(index) if *index < T::N_CHOICES => Ok(T::from_index(*index)),
+            ParamValue::Categorical(_) => Err(Error::Internal("categorical index out of bounds")),
             _ => Err(Error::Internal(
                 "Categorical distribution should return Categorical value",
             )),
@@ -887,6 +892,17 @@ mod tests {
         assert!(param.cast_param_value(&ParamValue::Float(1.0)).is_err());
     }
 
+    #[test]
+    fn categorical_param_cast_out_of_bounds() {
+        let param = CategoricalParam::new(vec!["sgd", "adam", "rmsprop"]);
+        assert!(param.cast_param_value(&ParamValue::Categorical(3)).is_err());
+        assert!(
+            param
+                .cast_param_value(&ParamValue::Categorical(usize::MAX))
+                .is_err()
+        );
+    }
+
     #[test]
     fn bool_param_distribution() {
         let param = BoolParam::new();
@@ -955,6 +971,17 @@ mod tests {
         assert!(param.cast_param_value(&ParamValue::Float(1.0)).is_err());
     }
 
+    #[test]
+    fn enum_param_cast_out_of_bounds() {
+        let param = EnumParam::<TestEnum>::new();
+        assert!(param.cast_param_value(&ParamValue::Categorical(3)).is_err());
+        assert!(
+            param
+                .cast_param_value(&ParamValue::Categorical(usize::MAX))
+                .is_err()
+        );
+    }
+
     #[test]
     fn float_param_suggest_via_trial() {
         let param = FloatParam::new(0.0, 1.0);