From 89a725f664a6984eb7a4e206ccf208e2c8d0cee6 Mon Sep 17 00:00:00 2001
From: MrSpoony <kimi.loeffel@hispeed.ch>
Date: Thu, 9 Mar 2023 09:11:12 +0100
Subject: [PATCH] add string to number

---
 string-to-number.ts | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 string-to-number.ts

diff --git a/string-to-number.ts b/string-to-number.ts
new file mode 100644
index 0000000..bc7ef04
--- /dev/null
+++ b/string-to-number.ts
@@ -0,0 +1,31 @@
+import type { Equal, Expect } from '@type-challenges/utils'
+
+type cases = [
+  Expect<Equal<ToNumber<'0'>, 0>>,
+  Expect<Equal<ToNumber<'5'>, 5>>,
+  Expect<Equal<ToNumber<'12'>, 12>>,
+  Expect<Equal<ToNumber<'27'>, 27>>,
+  Expect<Equal<ToNumber<'18@7_$%'>, never>>,
+]
+
+type Digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';
+
+type IsNumber<
+  S extends string,
+> =
+S extends `${Digit}${infer Tail}`
+  ? IsNumber<Tail>
+  : S extends ''
+    ? true
+    : false
+;
+
+type ToNumber<
+  S extends string,
+  Acc extends 1[] = []
+> =
+IsNumber<S> extends true
+  ? `${Acc['length']}` extends S
+    ? Acc['length']
+    : ToNumber<S, [...Acc, 1]>
+  : never