From 2cd4ebffbee70bd2cf551c7a59a19c05fe04e34b Mon Sep 17 00:00:00 2001
From: Sophia Sam <sophia.sam@lever.co>
Date: Wed, 11 Sep 2024 11:14:09 -0400
Subject: [PATCH 1/3] Fix model.start type for 2-way funcs

---
 src/Model/fn.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/Model/fn.ts b/src/Model/fn.ts
index 6d15b9ff..f0d215c5 100644
--- a/src/Model/fn.ts
+++ b/src/Model/fn.ts
@@ -10,10 +10,10 @@ class NamedFns { }
 type StartFnParam = unknown;
 
 type ModelFn<Ins extends unknown[], Out> =
-  (...inputs: Ins) => Out |
+  ((...inputs: Ins) => Out) |
   {
-    get(...inputs: Ins): Out,
-    set(output: Out, ...inputs: Ins): void,
+    get(...inputs: Ins): Out;
+    set(output: Out, ...inputs: Ins): {[key: number] : Ins[number]} | Ins[] | null;
   };
 
 interface ModelStartOptions {

From f09052a4a17b2092c9f60dd6e65478afa45143ac Mon Sep 17 00:00:00 2001
From: Sophia Sam <sophia.sam@lever.co>
Date: Wed, 11 Sep 2024 11:25:56 -0400
Subject: [PATCH 2/3] Change to commas

---
 src/Model/fn.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Model/fn.ts b/src/Model/fn.ts
index f0d215c5..68a72a32 100644
--- a/src/Model/fn.ts
+++ b/src/Model/fn.ts
@@ -12,8 +12,8 @@ type StartFnParam = unknown;
 type ModelFn<Ins extends unknown[], Out> =
   ((...inputs: Ins) => Out) |
   {
-    get(...inputs: Ins): Out;
-    set(output: Out, ...inputs: Ins): {[key: number] : Ins[number]} | Ins[] | null;
+    get(...inputs: Ins): Out,
+    set(output: Out, ...inputs: Ins): {[key: number] : Ins[number]} | Ins[] | null,
   };
 
 interface ModelStartOptions {

From 55bd241f805e0e4052041ab1d41809f20af62647 Mon Sep 17 00:00:00 2001
From: Eric Hwang <ericyhwang@users.noreply.github.com>
Date: Thu, 12 Sep 2024 15:15:39 -0700
Subject: [PATCH 3/3] Further updates to 2-way reactive function set() types

- Allow `set()` to return a partial array covering first N inputs to update, and remove extra brackets in `Ins[]` return type since `Ins` is already an array
- Individually validate types of each item of of `{ 0: in0, 2: in2, ... }` object return value, instead of using an index signature that allows values to be any of the inputs' types
---
 src/Model/fn.ts | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/Model/fn.ts b/src/Model/fn.ts
index 68a72a32..c66ba73d 100644
--- a/src/Model/fn.ts
+++ b/src/Model/fn.ts
@@ -9,11 +9,20 @@ class NamedFns { }
 
 type StartFnParam = unknown;
 
+// From type-fest: https://github.com/sindresorhus/type-fest
+type ArrayIndices<Element extends readonly unknown[]> =
+  Exclude<Partial<Element>['length'], Element['length']>;
+
+type TwoWayReactiveFnSetReturnType<Ins extends readonly unknown[]> =
+  Partial<Ins> |
+  Partial<{ [K in Extract<ArrayIndices<Ins>, number>]: Ins[K] }> |
+  null;
+
 type ModelFn<Ins extends unknown[], Out> =
   ((...inputs: Ins) => Out) |
   {
-    get(...inputs: Ins): Out,
-    set(output: Out, ...inputs: Ins): {[key: number] : Ins[number]} | Ins[] | null,
+    get(...inputs: Ins): Out;
+    set(output: Out, ...inputs: Ins): TwoWayReactiveFnSetReturnType<Ins>;
   };
 
 interface ModelStartOptions {
@@ -99,11 +108,7 @@ declare module './Model' {
      */
     fn<Ins extends unknown[], Out>(
       name: string,
-      fn: (...inputs: Ins) => Out |
-        {
-          get(...inputs: Ins): Out;
-          set(output: Out, ...inputs: Ins): void
-        }
+      fn: ModelFn<Ins, Out>
     ): void;
 
     /**