Implement invade helper

Author: NoelDeMartin

src/fluent/index.ts

@@ -76,3 +76,5 @@ export type { FluentArray, FluentArrayHelpers, FluentArrayInstance } from './Flu
 
 export { default as FluentStringDefinition, fluentStringHelpers } from './FluentString';
 export type { FluentString, FluentStringInstance } from './FluentString';
+
+export * from './invade';

src/fluent/invade.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from 'vitest';
+
+import { invade } from './invade';
+
+describe('invade', () => {
+
+    it('invades private methods', () => {
+        class Vault {
+
+            private getSecret(): string {
+                return '42';
+            }
+        
+        }
+
+        expect(invade(new Vault(), ['getSecret']).getSecret()).toBe('42');
+    });
+
+});

src/fluent/invade.ts

@@ -0,0 +1,9 @@
+import type { Override } from '@noeldemartin/utils/types';
+
+// @ts-expect-error Allow invades
+export type Invaded<TObject, TMethods extends string> = { [K in TMethods]: TObject[K] };
+
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+export function invade<T, TMethods extends string>(object: T, methods: TMethods[]): Override<T, Invaded<T, TMethods>> {
+    return object as Override<T, Invaded<T, TMethods>>;
+}

src/types/helpers.ts

@@ -23,6 +23,7 @@ export type ObjectValues<T> = T[keyof T];
 export type OnlyKnownProperties<TGeneric, TKnown> = {
     [K in keyof TGeneric]: K extends keyof TKnown ? TGeneric[K] : never;
 };
+export type Override<T, TOverrides> = Omit<T, keyof TOverrides> & TOverrides;
 export type Pretty<T> = T extends infer U ? { [K in keyof U]: U[K] } : never;
 export type SubPartial<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>>;
 export type TypeGuard<T = unknown> = (value: unknown) => value is T;