feat: ✨ Add TupleElementAt

CRBroughton · Oct 23, 2024 · e57f22a · e57f22a
1 parent ff6e32f
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diff --git a/.changeset/fresh-tigers-pull.md 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
@@ -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
@@ -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>>
+//   ^?