Now that we are a bit familiar with basic Kotlin syntax, we can move on to discuss what design patterns are all about.
Introduction to design patterns
What are design patterns?
There are different misconceptions surrounding design patterns. In general, they are as follows:
- Missing language features
- Not necessary in dynamic language
- Relevant only to object-oriented languages
- Relevant only to enterprises
But actually, design patterns are just a proven way to solve a common problem. As a concept, they are not limited to a specific programming language (Java), nor to a family of languages (C-family, for example), nor are they limited to programming in general. You may have even heard of design patterns in software architecture, which discuss how different systems can efficiently communicate with each other. There are service-oriented architectural patterns, which you may know as Service-Oriented Architecture (SOA), and microservice design patterns that evolved from SOA and emerged over the past few years. The future will, for sure, bring us even more design pattern families.
Even in the physical world, outside software development, we're surrounded by design patterns and commonly accepted solutions to a certain problem. Let's look at an example.
Design patterns in real life
Did you ride an elevator lately? Was there a mirror on the wall of the elevator? Why is that?
How did you feel when you last rode an elevator that had no mirror and no glass walls?
The main reason we commonly have mirrors in our elevators is to solve a common problem. Riding in an elevator is boring. We could put in a picture. But a picture would also get boring after a while, if you rode the same elevator at least twice a day. Cheap, but not much of an improvement.
We could put in a TV screen, as some do. But it makes the elevator more expensive. And it also requires a lot of maintenance. We need to put some content on the screen, to make it not too repetitive. So either there's a person whose responsibility is to renew the content once in a while, or a third-party company that does it for us. We'll also have to handle different problems that may occur with screen hardware and the software behind it. Seeing the "Blue Screen of Death" is amusing, of course, but only mildly.
Some architects even go for putting elevator shafts on the building exterior, and making part of the walls transparent. This may provide some exciting views. But this solution also requires maintenance (dirty windows don't make for the best view), and a lot of architectural planning.
So, we put in a mirror. You get to watch an attractive person even if you ride alone. Some studies indicate that we find ourselves more attractive than we are, anyway. Maybe you get a chance to review your appearances one last time before that important meeting. Mirrors visually expand the visual space and make the entire trip less claustrophobic, or less awkward, if it's the start of a day and the elevator is really crowded.
Design process
Let's try and understand what we did just now.
We didn't invent mirrors in elevators. We've seen them thousands of times. But we formalized the problem (riding in an elevator is boring) and discussed alternative solutions (TV screens, glass walls) and the benefits of the commonly used solution (solves the problem, easy to implement). That's what design patterns are all about.
The basic steps of the design process are:
- Define exactly what the current problem is.
- Consider different alternatives, based on the pros and cons.
- Choose the solution that solves the problem, while best fitting your specific constraints.
Why use design patterns in Kotlin?
Kotlin comes to solve the real-world problems of today. In the following chapters, we will discuss both Design Patterns first introduced by the Gang of Four back in '94, as well as design patterns that emerged from the functional programming paradigm.
You'll find that some of the design patterns are so common or useful that they're already built into the language as reserved keywords or standard functions. Some of them will need to combine a set of language features. And some are not so useful any more, since the world has moved forward, and they're being replaced by some other patterns.
But in any case, familiarity with design patterns and best practices expands your "developer toolbox" and creates shared vocabulary between you and your colleagues.
