Add Function: withLet (#68)

.changeset/curvy-files-heal.md

@@ -0,0 +1,5 @@
+---
+"@bryx-inc/ts-utils": minor
+---
+
+Introduce `withLet` function

src/function.test.ts

@@ -1,4 +1,4 @@
-import { createCurriedGuardPredicate, pipe, tryOr, inject } from "./function";
+import { createCurriedGuardPredicate, pipe, tryOr, inject, withLet } from "./function";
 import { castUnsafe } from "./object";
 
 test("create curried guard predicate", () => {
@@ -50,3 +50,7 @@ test("inject", () => {
     expect(fn1).toHaveBeenCalledTimes(arr.length);
     expect(fn2).toHaveBeenCalledTimes(arr.length);
 });
+
+test("withLet", () => {
+    expect(withLet(1 + 2 + 3, (it) => it + 4)).toEqual(1 + 2 + 3 + 4);
+});

src/function.ts

@@ -147,3 +147,27 @@ export function inject<T>(fn: (arg: T) => unknown): (arg: T) => T {
         return arg;
     };
 }
+
+/**
+ * Apply a callback function to a value and return the result.
+ *
+ * @param {T} val - The value to be passed to the callback function.
+ * @param {(it: T) => E} fn - The callback function that processes the value.
+ * @returns {E} The result of applying the callback function to the value.
+ *
+ * @example
+ * ```ts
+ * type Data =
+ *   | { type: "gizmo" }
+ *   | { type: "shape", sides: number };
+ *
+ * function getData(): Data {
+ *   // ...
+ * }
+ *
+ * const sides = withLet(getData(), it => it.type == "shape" ? it.sides : 0);
+ * ```
+ */
+export function withLet<T, E = T>(val: T, fn: (it: T) => E): E {
+    return fn(val);
+}

src/object.ts

@@ -1,6 +1,5 @@
 import { cond } from "./condition";
-import { throwError } from "./errors";
-import { isNone, Maybe } from "./maybe";
+import { Maybe } from "./maybe";
 import { DeepKeyOf, DeepPick, DeepValue } from "./types";
 
 /* eslint-disable-next-line @typescript-eslint/no-unused-vars */