From 25f27026f0892714f5b1d4c6a8dca5b9bcf7a6fa Mon Sep 17 00:00:00 2001
From: "Emil J. Tywoniak" <emil@tywoniak.eu>
Date: Wed, 17 Jun 2026 00:05:52 +0200
Subject: [PATCH] newcelltypes: twines

---
 kernel/newcelltypes.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/newcelltypes.h b/kernel/newcelltypes.h
index be528d32c..58a685386 100644
--- a/kernel/newcelltypes.h
+++ b/kernel/newcelltypes.h
@@ -455,8 +455,10 @@ struct Categories {
 		constexpr bool operator[](size_t idx) {
 			return data[idx];
 		}
-		constexpr void set_id(IdString type, bool val = true) {
-			size_t idx = type.index_;
+		// Indexed by TwineRef value, matching operator() and the Categories
+		// constructor.
+		constexpr void set_id(TwineRef type, bool val = true) {
+			size_t idx = type;
 			if (idx >= MAX_CELLS)
 				return; // TODO should be an assert but then it's not constexpr
 			data[idx] = val;