From 4c2b406c5878fdd16900b8a0ca2878379abdb5ca Mon Sep 17 00:00:00 2001
From: Matt Pocock <mattpocockvoice@gmail.com>
Date: Wed, 22 Feb 2023 12:13:53 +0000
Subject: [PATCH] Attempted fix for #48

---
 src/entrypoints/is-array.d.ts |  2 +-
 src/entrypoints/utils.d.ts    |  2 ++
 src/tests/is-array.ts         | 14 ++++++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/entrypoints/is-array.d.ts b/src/entrypoints/is-array.d.ts
index 199bc66..cd5f8d8 100644
--- a/src/entrypoints/is-array.d.ts
+++ b/src/entrypoints/is-array.d.ts
@@ -1,3 +1,3 @@
 interface ArrayConstructor {
-  isArray(arg: any): arg is unknown[];
+  isArray<T>(arg: T): arg is unknown extends T ? unknown[] : any[];
 }
diff --git a/src/entrypoints/utils.d.ts b/src/entrypoints/utils.d.ts
index 00171cb..34d5346 100644
--- a/src/entrypoints/utils.d.ts
+++ b/src/entrypoints/utils.d.ts
@@ -14,4 +14,6 @@ declare namespace TSReset {
     : T extends symbol
     ? symbol
     : T;
+
+  type Cast<A, B> = A extends B ? A : B;
 }
diff --git a/src/tests/is-array.ts b/src/tests/is-array.ts
index daaa12c..a5a8b0a 100644
--- a/src/tests/is-array.ts
+++ b/src/tests/is-array.ts
@@ -23,3 +23,17 @@ doNotExecute(() => {
 
   type tests = [Expect<Equal<typeof paths, string[]>>];
 });
+
+doNotExecute(() => {
+  type Unarray<T> = T extends Array<infer U> ? U : T;
+
+  function test<T>(value: T) {
+    const inner = <X extends Unarray<T>>(v: X[]) => {
+      //
+    };
+
+    if (Array.isArray(value)) {
+      inner(value);
+    }
+  }
+});