From 41e24a1e4f2705901702bdaeeb42d9349bb989e1 Mon Sep 17 00:00:00 2001
From: Rickard Andersson <gonz@severnatazvezda.com>
Date: Thu, 3 Aug 2023 10:53:58 +0300
Subject: [PATCH] feat(dev): add `assertUnreachable`

Asserts that a case is unreachable in `switch` statements (and really
any flow control construct)
---
 src/utilities.ts | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 src/utilities.ts

diff --git a/src/utilities.ts b/src/utilities.ts
new file mode 100644
index 00000000..5ab5221e
--- /dev/null
+++ b/src/utilities.ts
@@ -0,0 +1,18 @@
+/**
+ * Asserts that a case in a switch statement is unreachable.
+ *
+ * @example
+ * // Exhaustively checks `user.role` type ("admin" | "user") and will not compile
+ * // if a new role is added without adding a case to the switch statement.
+ * switch (user.role) {
+ *    case "admin":
+ *       break;
+ *    case "user":
+ *      break;
+ *    default:
+ *      assertUnreachable(user.role);
+ * }
+ */
+export function assertUnreachable(value: never): never {
+    throw new Error(`Unreachable case: ${value}`);
+}