feat(api): added the Init type

thi-ng · Jan 5, 2020 · f6c333a · f6c333a
1 parent 44ae2f7
commit f6c333a
Showing 1 changed file with 13 additions and 0 deletions.
diff --git a/packages/api/src/api/tuple.ts b/packages/api/src/api/tuple.ts
@@ -57,3 +57,16 @@ export type Last<T extends unknown[]> = {
     0: Head<T>;
     1: Last<Tail<T>>;
 }[Tail<T> extends [] ? 0 : 1];
+
+/**
+ * Internal version of Init accepting 1 extra argument for the accumulated value.
+ */
+type InitReducer<T extends unknown[], C extends unknown[] = []> = {
+    0: Reverse<C>;
+    1: InitReducer<Tail<T>, Prepend<Head<T>, C>>;
+}[Tail<T> extends [] ? 0 : 1];
+
+/**
+ * Extracts everything except the last element from a tuple.
+ */
+export type Init<T extends unknown[]> = InitReducer<T>;