diff --git a/src/factor_graph.rs b/src/factor_graph.rs
index 150a995..d1d45c7 100644
--- a/src/factor_graph.rs
+++ b/src/factor_graph.rs
@@ -10,31 +10,25 @@ pub use message::*;
 pub use variable::*;
 
 pub struct PriorFactor {
-    id: MessageId,
+    variable_msg: MessageId,
     variable: VariableId,
     gaussian: Gaussian,
 }
 
 impl PriorFactor {
-    pub fn new(
-        message_arena: &mut MessageArena,
-        variable: VariableId,
-        gaussian: Gaussian,
-    ) -> PriorFactor {
-        let id = message_arena.create();
-
-        PriorFactor {
-            id,
+    pub fn new(message_arena: &mut MessageArena, variable: VariableId, gaussian: Gaussian) -> Self {
+        Self {
+            variable_msg: message_arena.create(),
             variable,
             gaussian,
         }
     }
 
     pub fn start(&self, variable_arena: &mut VariableArena, message_arena: &mut MessageArena) {
-        let old = message_arena[self.id];
+        let old = message_arena[self.variable_msg];
         let value = variable_arena[self.variable];
 
-        message_arena[self.id] = self.gaussian * old / value;
+        message_arena[self.variable_msg] = self.gaussian * old / value;
         variable_arena[self.variable] = self.gaussian;
     }
 }
@@ -53,8 +47,8 @@ impl LikelihoodFactor {
         mean: VariableId,
         value: VariableId,
         variance: f64,
-    ) -> LikelihoodFactor {
-        LikelihoodFactor {
+    ) -> Self {
+        Self {
             mean_msg: message_arena.create(),
             value_msg: message_arena.create(),
             mean,
@@ -112,8 +106,8 @@ impl SumFactor {
         sum: VariableId,
         terms: Vec<VariableId>,
         coeffs: Vec<f64>,
-    ) -> SumFactor {
-        SumFactor {
+    ) -> Self {
+        Self {
             sum_msg: message_arena.create(),
             terms_msg: terms
                 .iter()
@@ -265,8 +259,8 @@ impl TruncateFactor {
         variable: VariableId,
         epsilon: f64,
         draw: bool,
-    ) -> TruncateFactor {
-        TruncateFactor {
+    ) -> Self {
+        Self {
             variable_msg: message_arena.create(),
             variable,
             epsilon,