Merge pull request #261 from ryoppippi/feature/257

feat(concat): Add concat function and tests

Author: ryoppippi

src/cocat.test.ts

@@ -0,0 +1,24 @@
+import { assertEquals } from "assert";
+import type { AssertTrue, IsExact } from "type-testing";
+import { concat } from "./concat.ts";
+
+Deno.test("should concat one string", () => {
+  const concated = concat("a");
+  const expected = "a" as const;
+  assertEquals(concated, expected);
+  type _ = AssertTrue<IsExact<typeof expected, typeof concated>>;
+});
+
+Deno.test("should concat multiple strings", () => {
+  const concated = concat("hello", "world");
+  const expected = "helloworld" as const;
+  assertEquals(concated, expected);
+  type _ = AssertTrue<IsExact<typeof expected, typeof concated>>;
+});
+
+Deno.test("should concat multiple strings with a separator", () => {
+  const concated = concat("hello", " ", "world");
+  const expected = "hello world" as const;
+  assertEquals(concated, expected);
+  type _ = AssertTrue<IsExact<typeof expected, typeof concated>>;
+});

src/concat.ts

@@ -0,0 +1,34 @@
+import type * as TF from "type-fest";
+
+type ConcatingLoop<
+  T extends readonly string[],
+  R extends string = "",
+> = [] extends T ? R
+  : TF.IsStringLiteral<R> extends true
+    ? T extends [infer A, ...infer B]
+      ? B extends readonly string[]
+        ? A extends string ? ConcatingLoop<B, `${R}${A}`>
+        : string
+      : string
+    : string
+  : string;
+
+type ConcatedString<T extends readonly string[]> = ConcatingLoop<T>;
+
+/**
+ * concat strings
+ *
+ * ```ts
+ * import { concat } from '@ryoppippi/str-fns'
+ * const _: 'a' = concat('a');
+ * const __: 'helloworld' = concat('hello', 'world');
+ * const ___: 'hello world' = concat('hello', ' ', 'world');
+ * ```
+ *
+ * @param ...inputs - strings to concat
+ */
+export function concat<T extends readonly string[]>(
+  ...inputs: T
+): ConcatedString<T> {
+  return "".concat(...inputs) as ConcatedString<T>;
+}

src/index.ts

@@ -3,3 +3,4 @@ export * from "./uncapitalize.ts";
 export * from "./lowercase.ts";
 export * from "./uppercase.ts";
 export * from "./split.ts";
+export * from "./concat.ts";