From e57f22ac9b140b961cb304bd4ab788bf4ce1c1e1 Mon Sep 17 00:00:00 2001
From: CRBroughton <crbroughton@posteo.uk>
Date: Wed, 23 Oct 2024 21:21:09 +0100
Subject: [PATCH] feat: :sparkles: Add TupleElementAt

---
 .changeset/fresh-tigers-pull.md |  5 +++++
 index.ts                        |  2 ++
 tests/TupleElementAt.test.ts    | 11 +++++++++++
 3 files changed, 18 insertions(+)
 create mode 100644 .changeset/fresh-tigers-pull.md
 create mode 100644 tests/TupleElementAt.test.ts

diff --git a/.changeset/fresh-tigers-pull.md b/.changeset/fresh-tigers-pull.md
new file mode 100644
index 0000000..9c0835c
--- /dev/null
+++ b/.changeset/fresh-tigers-pull.md
@@ -0,0 +1,5 @@
+---
+"@crbroughton/ts-test-utils": minor
+---
+
+Add TupleElementAt
diff --git a/index.ts b/index.ts
index d856fcd..5da94d9 100644
--- a/index.ts
+++ b/index.ts
@@ -61,6 +61,8 @@ export type GetParameters<T> = T extends (...args: infer P) => any ? P : never
 
 export type GetArrayUnion<T> = T extends readonly (infer U)[] ? U : never
 
+export type TupleElementAt<T extends unknown[], Index extends number> = T[Index]
+
 export type DeepReturnType<T> =
   T extends (...args: unknown[]) => infer ReturnType
     ? ReturnType extends (...args: unknown[]) => unknown
diff --git a/tests/TupleElementAt.test.ts b/tests/TupleElementAt.test.ts
new file mode 100644
index 0000000..429f4d0
--- /dev/null
+++ b/tests/TupleElementAt.test.ts
@@ -0,0 +1,11 @@
+/* eslint-disable unused-imports/no-unused-vars */
+import type { Equals, Expect, TupleElementAt } from '..'
+
+// Passes the assignable test when the first type is assignable
+type Result = Expect<Equals<TupleElementAt<['a', 'b', 'c'], 1>, 'b'>>
+//   ^?
+
+// Failed the TupleElementAt test - non-narrowed to the literal string
+// @ts-expect-error - Fails the exclusion
+type ResultFailure = Expect<Equals<TupleElementAt<['a', 'b', 'c'], 1>, string>>
+//   ^?