add intersection

3 years ago · 1136e6c59e
parent 89a725f664
commit 1136e6c59e
1 changed files with 31 additions and 0 deletions
--- a/intersection.ts
+++ b/intersection.ts
@ -0,0 +1,31 @@
+import type { Equal, Expect } from '@type-challenges/utils'
+
+type cases = [
+  Expect<Equal<Intersection<[[1, 2], [2, 3], [2, 2]]>, 2>>,
+  Expect<Equal<Intersection<[[1, 2, 3], [2, 3, 4], [2, 2, 3]]>, 2 | 3>>,
+  Expect<Equal<Intersection<[[1, 2], [3, 4], [5, 6]]>, never>>,
+  Expect<Equal<Intersection<[[1, 2, 3], [2, 3, 4], 3]>, 3>>,
+  Expect<Equal<Intersection<[[1, 2, 3], 2 | 3 | 4, 2 | 3]>, 2 | 3>>,
+  Expect<Equal<Intersection<[[1, 2, 3], 2, 3]>, never>>,
+];
+
+type ToUnion<T extends unknown[]> = T[number];
+
+type Intersect<T, U> = T & U;
+
+type Intersection<
+  T
+> = 
+T extends [infer First, infer Second, ...infer Tail]
+  ? First extends number[]
+    ? Second extends number[]
+      ? Intersection<[Intersect<ToUnion<First>, ToUnion<Second>>, ...Tail]>
+      : Intersection<[Intersect<ToUnion<First>, Second>, ...Tail]>
+    : Intersection<[Intersect<First, Second>, ...Tail]>
+  : T extends [infer Head, ...infer Tail]
+    ? Head extends number[]
+      ? ToUnion<Head>
+      : Head
+    : never
+;
+