Multiple Inheritance in Kawkab

In JavaScript and TypeScript, multiple inheritance is not directly supported, which presents a challenge for developers who need to combine multiple behaviors from different objects or services. However, Kawkab has introduced an innovative solution to this problem using the inherit function, enabling multiple inheritance in a flexible and easy way.

What is Multiple Inheritance?

Multiple inheritance is a programming pattern that allows you to make one object inherit from multiple objects or classes simultaneously. In languages that directly support multiple inheritance (like C++), an object can easily obtain properties and behaviors from multiple sources. However, JavaScript and TypeScript don’t directly support this pattern; they only allow objects to inherit from a single object.

The Multiple Inheritance Problem in JavaScript and TypeScript

In JavaScript and TypeScript, objects can only inherit from one object. For example, you can’t write something like:

class Child extends ParentA, ParentB {}

This limitation is not supported in JavaScript or TypeScript. However, if you have multiple classes with shared functions or behaviors you want to combine, there are alternative solutions like using Mixins or Prototype-based inheritance.

The Solution in Kawkab Using `inherit`

The inherit function in Kawkab allows you to combine multiple behaviors from multiple classes into a single class, providing a flexible solution for multiple inheritance. This function allows you to easily merge multiple functionalities into one class, enhancing code organization and helping reduce duplication.

How Does `inherit` Work?

The inherit function is used to combine multiple classes together, allowing you to leverage the properties of inherited classes in a new class. inherit can be used with any class whose behaviors you want to combine, enabling dynamic and flexible behavior merging.

How to Use Multiple Inheritance in Kawkab?

Example of Multiple Inheritance Using `inherit`

In this example, we use inherit to combine the BaseService class and Inject class into the WelcomeService class.

import { BaseService, Inject, inherit } from "kawkab";
 
export class WelcomeService extends inherit(BaseService, Inject) {
    /**
     * Return a welcome message
     * @returns {string} The welcome message
     */
    message() {
        return "Welcome to Kawkab Framework 🚀!";
    }
}

Example Explanation:

BaseService: Contains the basic functions needed by application services.
Inject: Allows you to inject dependencies into the class, making object management easier within the application.
inherit: Combines the BaseService and Inject classes into one class, allowing you to use functions from both classes within WelcomeService.

Using Multiple Inheritance in Controllers

You can use combined classes in Kawkab within Controllers. For example, we can use WelcomeService that inherits from BaseService and Inject inside a controller like this:

import { BaseController, inherit } from "kawkab";
import { WelcomeService } from "../services/welcome";
import { Docs } from "./docs";
import { Middleware } from "./middleware";
 
export default class extends inherit(BaseController, Middleware, Docs) {
    constructor(private welcomeService = WelcomeService.inject()) {
        super();
    }
 
    /**
     * GET function to return welcome message
     * @returns {object} JSON response
     */
    async get() {
        return {
            status: true,
            message: this.welcomeService.message(),
        };
    }
}

Process Explanation:

Creating a Service:
WelcomeService is defined using inherit to combine BaseService, Middleware, and Docs.
Injecting the Service:
Inside the controller, .inject() is used to call WelcomeService.
Using Functions:
After injecting the service, you can call functions like message() that were inherited from other classes.

Benefits of Multiple Inheritance Using `inherit`

Reducing Code Duplication:
Using inherit, you can combine multiple behaviors into one class, reducing the need for code duplication in your application.
Reusability:
The combined class can be used in different places without needing to recreate it.
Easy Maintenance:
When you need to modify or add new behavior, you can modify the original class instead of modifying multiple objects.
Design Flexibility:
inherit gives you great flexibility in combining classes without worrying about single inheritance constraints.

Best Practices for Using Multiple Inheritance

Use inherit Moderately:
Make sure you need to combine multiple functions from multiple sources. If some functions are unnecessary, it might be better to keep them separate.
Organize Classes Well:
Make sure to organize classes in appropriate folders, like /services and /controllers, for easy maintenance.
Using inherit:
Ensure you use inheritance in an organized and effective way to ensure future scalability.
Unit Testing:
Use Mock Services when testing units to ensure test coverage for all possible scenarios.

Summary

Multiple inheritance is a concept not directly supported in JavaScript and TypeScript. However, using Kawkab and the inherit function, you can combine multiple behaviors from several objects into a single class. This solution provides great flexibility and makes code management easier in large applications, while reducing duplication and enhancing maintainability.

Application Lifecycle Dependency Injection