From 261acca8a47201f63917984a8a0a1983559911d0 Mon Sep 17 00:00:00 2001
From: George Thomas <georgefsthomas@gmail.com>
Date: Thu, 19 Feb 2026 21:11:23 +0000
Subject: [PATCH] Define nicer Rust tree type and coerce

---
 rust/lib.rs | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/rust/lib.rs b/rust/lib.rs
index c471ecb..07b0887 100644
--- a/rust/lib.rs
+++ b/rust/lib.rs
@@ -42,7 +42,20 @@ extern "C" fn add(a: i64, b: i64) -> i64 {
 }
 
 #[repr(C)]
-#[derive(Clone, Copy)]
+enum BTreeBox {
+    Leaf { value: i64 },
+    Fork { left: Box<BTreeBox>, right: Box<BTreeBox> },
+}
+impl BTreeBox {
+    fn sum(&self) -> i64 {
+        match self {
+            BTreeBox::Leaf { value } => *value,
+            BTreeBox::Fork { left, right } => left.sum() + right.sum(),
+        }
+    }
+}
+
+#[repr(C)]
 enum BTree {
     Leaf {
         value: i64,
@@ -55,8 +68,5 @@ enum BTree {
 
 #[unsafe(no_mangle)]
 extern "C" fn sum_tree(t: BTree) -> i64 {
-    match t {
-        BTree::Leaf { value } => value,
-        BTree::Fork { left, right } => unsafe { sum_tree(*left) + sum_tree(*right) },
-    }
+    (unsafe { std::mem::transmute::<_, &BTreeBox>(&t) }).sum()
 }