Design patterns overview

Implementing solutions that use design patterns save us hours of time in debugging making the codebase robust and reusable.
Design pattern helps to develop structured codebase and maintain it easily in check with SOLID principles.

Sometimes we want to restrict the total number of instances that can be created of a particular object.
Example: Wifi router is shared by all family members. In this case single wifi connection being consumed by multiple members.

Ensure that the structure defined for our classes/objects is efficient and flexible so that it can be easily composed with other objects.
When we use extends or implements, we use some form of Structural Design Pattern.

Allows two completely different objects to understand and communicate with each other.
Example: There will be a wrapper class which will take input/recieve information from different sources. Then convert all inputs to a particular format of cosumer needs.

Best way to facilitate compostion into our application.
Each module will represent an independent part of our applicaion which can be assembled into a more complex application.
Make codebase organized and extremely reusable.
Example: Implementing Auth in different applications. There will a an Auth class with authorize() method in it. User class will call this method to login.

Extension of Module pattern.
Once we create independent modules, all of these can be implement to form a complex application.
Like our smartphone, that is made of so many different pieces like a display, battery, microphone, memory unit, camera, and so on.
Example: We can implement a Logger module in our User service. Thus User service will have two modules: Auth, Logger.

Aim at defining how objects can communicate each other in a flexible way.
If we ever user a Publiser/Subscriber model, message queue or UI framework, then we used that pattern.
2 main flavour:
- Push based: Change notification is pushed to subscribers. Like socket.
- Pull based: Objects keep polling from subscriber to get updates. Like REST APIs.
Example: When we follow someone in social media, we except to recieve all of the updates of the publisher. Push based observer pattern is the perfect solution in this case.

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