feat(api): add Select2/3/4 conditional types

thi-ng · Jun 14, 2019 · a4bfb88 · a4bfb88
1 parent 9e3bfde
commit a4bfb88
Showing 1 changed file with 16 additions and 0 deletions.
diff --git a/packages/api/src/api.ts b/packages/api/src/api.ts
@@ -297,6 +297,22 @@ export type Predicate<T> = Fn<T, boolean>;
  */
 export type Predicate2<T> = Fn2<T, T, boolean>;
 
+export type Select2<T, Q, A, B> = T extends Q ? A : B;
+
+export type Select3<T, Q1, Q2, A, B, C> = T extends Q1
+    ? A
+    : T extends Q2
+    ? B
+    : C;
+
+export type Select4<T, Q1, Q2, Q3, A, B, C, D> = T extends Q1
+    ? A
+    : T extends Q2
+    ? B
+    : T extends Q3
+    ? C
+    : D;
+
 /**
  * Higher order `Predicate` builder. Possibly stateful.
  */