From 93621f28e140a36cc2e2fd8cc7e615564c03e795 Mon Sep 17 00:00:00 2001
From: Nao Pross <np@0hm.ch>
Date: Sat, 2 Mar 2024 21:53:07 +0100
Subject: Make state.State a dataclass

Also, the members were (incorrectly) not instance variables
---
 mdpoly/state.py | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/mdpoly/state.py b/mdpoly/state.py
index 1ba44fe..739ec7a 100644
--- a/mdpoly/state.py
+++ b/mdpoly/state.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 from typing import TYPE_CHECKING
+from dataclasses import dataclass, field
 
 if TYPE_CHECKING:
     from .types import Number
@@ -9,9 +10,10 @@ if TYPE_CHECKING:
 Index = int
 
 
+@dataclass
 class State:
-    variables: dict[Var, Index] = {}
-    parameters: dict[Param, Number] = {}
+    variables: dict[Var, Index] = field(default_factory=dict)
+    parameters: dict[Param, Number] = field(default_factory=dict)
     _last_index: Index = -1 
 
     def _make_index(self) -> Index:
@@ -28,6 +30,9 @@ class State:
 
         return self.variables[var]
 
-        
-
+    def from_index(self, index: Index) -> Var:
+        for var, idx in self.variables.items():
+            if idx == index:
+                return var
 
+        raise IndexError(f"There is no variable with index {index}.")
-- 
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