How to build DI in a multi-module iOS app using Needle

Let's briefly recall what modularization is, why it's needed, and what Dependency Injection has to do with it. Let's think about how this principle, or rather the framework that implements it, helps with modularization.

Next we will discuss why Needle is the best choice among the existing open source DI frameworks. Let's also talk about Needle itself - how it is designed and what are the nuances of using it.

In the end, we'll return to how to use it in a multi-module application and how to circumvent the problems it causes. Let's not ignore the topic of testing either - let's talk about how to write tests on code that uses Needle.