Systems can be organized granularly: we can split them into projects, made of multiple applications, containing several application-level layers, where we can have hundreds of modules, made up of thousands of functions, and so on. A granular approach helps us write code that’s easy to understand and maintain, by attaining a reasonable degree of modularity, while preserving our sanity. In section 1.4, we’ll discuss how we can best leverage this granularity to create modular applications.

This interface serves a dual purpose. It allows us to develop new bits and pieces of the component, only exposing functionality that’s ready for public consumption while keeping private everything that’s not meant to be shared with other components. At the same time, it allows consumers — that is, components or systems that are leveraging our interface — to reap the benefits of the functionality we expose, without concerning themselves with the details of how we implemented that functionality.

Relying on consistent API shapes is a great way of increasing productivity, given the difficulty of coming up with adequate interface designs. When we consistently leverage similar API shapes, we don’t have to come up with new designs every time, and consumers can rest assured that you haven’t reinvented the wheel every time. We’ll discuss API design at length over the coming chapters.