const app = {
lines: document.getElementById('lines'),
textbox: createTextbox(),
lineTemplate: createLineTemplate(),

const socket = connect(

initial({ lines, uuid, charLimit }) {
app.uuid = uuid
app.charLimit = charLimit

added(line) {

removed(i) {

server.onclose = (ws) => {
if (ws.line) {
const i = lines.indexOf(ws.line)
lines.splice(i, 1)
server.sendToAll({ removed: i })

server.commands = {

begin(ws) {
const line = {
hash: ws.hash,
uuid: ws.uuid,
text: '',

ws.line = line
server.sendToAll({ added: line })

run() {
console.log(`Running on port ${this.port}`)

this.wss = new WebSocket.Server({
port: this.port,
verifyClient: this.verify.bind(this)

this.pruneInterval * 1000


Steven Degutis

Full-stack software developer for hire

TDD Like You Mean It, and LSP

October 12, 2010

Today I essentially finished the SCNA5k Results website, using ATs and TDD the whole time! The last mile was to implement a JSON-based web service for downloading and uploading the list of runners, which took a little longer than I thought it would due to my inexperience with the tools, but overall was done fairly quickly. I can’t claim to be an expert at Cucumber or Capybara or Nokogiri or anything yet but I can say that it was definitely a good learning experience.

After that was finished, Eric and I shared a vim screen to do some pair-programming on TDD As If You Meant It. That was a lot of fun, especially when Eric’s network was up and he could connect. We eventually ended up on some very reasonable code for determining if a cell should be killed or resurrected, albeit seemingly simplistic code, but that’s the whole point: you get rid of your assumptions about what you think is needed to solve the problem, and you start with the actual problem domain, and work your way into a solution as bare-minimum as possible until the problem is technically solved, and with the bare minimum effort. This promotes properly encapsulated, functional code (and generally tends to promotes the Single-Responsibility Principle, from what I gather). Thus we started out with providing the solution directly in our tests, and once we noticed redundancy and shared business logic, we rafactored it (in between tests) into cleaner solution code. Overall, it made good sense and felt natural. I can’t wait to try it out on a larger-scale project and see what kind of code I write to solve a problem after getting rid of my assumptions and approaching the problems with a fresh perspective.

By the way, I was mistaken about what the Liskov Substitution Principle was on my previous blog post. It’s not just about an is-a relationship. It’s about behavior. In fact, throughout the entire article by Uncle Bob that I read on it, the best explanation is within only two paragraphs somewhere in the middle. It basically states that an object must behave like the classes it inherits from.

The behavior is the important thing here, and it’s based on Design By Contract. From the little reading I did on it throughout this article, DBC states that every function has a precondition which must be met in order for the function to run, and it guarantees a given state of the world, or postcondition.

This relates to the LSP in a very simple way: a subclass must require at most its superclass’s preconditions, and it must guarantee at least its superclass’s postconditions. (The article uses “weaker” and “stronger” but I find those to be less clear than this wording, which I prefer.) So for example, a Square is not a Rectangle in behavior, because its postcondition for its set_height function would not guarantee Rectangle’s postcondition that the width property remains the same as it was before the function’s execution. This exemplifies that it’s not really the properties of an object that matter here, but the behavior.

Interestingly enough, I’ve seen this before in Cocoa. It’s been satisfied by class clusters such as NSArray with its concrete, private subclass NSCFArray, which behaves exactly like an NSArray according to its external clients. (Granted, the LSP states that its internal behavior may be different, and that’s exactly the point of class clusters in the first place, so that doesn’t break the rule at all.) I’ve also seen Cocoa break the rule with Distributed Objects.

Mike Ash wrote a blog post going into detail about this behavior, specifically the point he makes where you may not add a distributed object proxy into an NSSet. It’s a little different than the plain-jane C++ example because ObjC also uses @protocols for its is-a behavior as well as inheritance, but it still holds just as well. Anything that conforms to the NSObject protocol should work just fine being added into an NSSet, but distributed objects (instances of class NSProxy, conforming to NSObject) might throw an exception upon receiving the message -hash, for instance, thus possibly putting the NSSet into an inconsistent state! Granted, this is arguable because there is no proof that NSSet cannot handle an exception thrown on a member’s -hash, and in fact there is no contract anywhere stating this. But given we have the rule that an object must never throw an exception from within -hash, this principle applies and thus is broken by DO.

About me


My name is Steven Degutis, and I've been writing software professionally for a decade. During that time, I've written many apps and websites, quite a few technical articles, and kept up-to-date with the rapidly evolving software industry.

If you have software needs for web, mobile, or desktop, and are looking for a seasoned software professional, please reach out to me at to set up a phone call.

Work Experience

  • Self-employed – present
  • Clean Coders – 5 years
  • 8th Light – 2 years
  • Big Nerd Ranch – 1 year
  • Self-employed - 1 year


  • Web: full-stack
  • iOS (UIKit)
  • macOS (Cocoa)
  • AWS / EC2 / ELB


  • JavaScript
  • HTML5 / CSS
  • Swift
  • Objective-C
  • Clojure


  • Node.js
  • Express.js
  • React
  • Vue.js
  • Electron

Technical articles

Over the past decade, I've written a total of 172 technical articles on various programming languages, frameworks, best practices, and my own projects, as I kept up-to-date and active in the software industry.

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Here are some of the projects I'm most proud of. They were created using a variety of technologies, running on several different platforms and OSes. They're all finished products, and many of them are open source.

Website - Online Video Store

I wrote this web store for Robert "Uncle Bob" Martin, using Clojure for the back-end, and JavaScript for the front-end. Over the course of 5 years, I took the site from a simple three-page website to a full enterprise-ready business solution, with nearly 100% test coverage.

  • Clojure
  • Datomic
  • jQuery / D3.js
  • JavaScript
  • ClojureScript


macOS app - Dock Utility

I made Docks in 2009 for users who wanted to swap out icons in their Dock with a single click. Its unique functionality and design aesthetic attracted the attention of Apple, Engadget, MacWorld, and led to an acquisition of my start-up by Big Nerd Ranch.

  • Staff Pick
  • MacWorld 4/5 Rating
  • MacWorld Gem of the Year
  • Featured on


macOS app - Clojure IDE

Source Code

While working on, a website written completely in Clojure, I increased my productivity by building a custom IDE for macOS designed specifically for Clojure projects.

  • Objective-C
  • Clojure
  • C / C++
  • Cocoa
  • Themeable


macOS app - Hackable Automation

Source Code

This began as an experiment to see how many languages I could use to script a custom macOS window manager using our custom TCP protocol. Eventually it had bindings for Clojure, Ruby, Python, Go, JavaScript, CoffeeScript, Node.js, Chicken Sceme, and Racket, as well as other community additions.

  • TCP / Unix sockets
  • Custom protocol
  • Highly Scriptable
  • 10+ language bindings
  • Open source community

Bubble Maker

iOS app - Bubble simulator

This toy was made in a weekend to entertain my 1 year old daughter. It lets you create bubbles with your fingers, which then simulate physics by bumping into each other and falling.

  • SpirteKit
  • Custom art
  • Physics simulation
  • iOS
  • tvOS

Quick List

iOS app - Todo list app

When I couldn't find an app in the App Store that let me make very simple lists extremely quickly, I made one myself. I use it almost every day to organize and track my activities.

  • In-app purchases
  • Custom UI / UX
  • Social media
  • App Store artwork
  • Spring animations

Website - Personal Portfolio

Source Code

This very site itself was written from scratch in about a day. It uses best practices for modern responsive web design, and a custom build phase to compile the sources into a single HTML file.

  • Node.js
  • Pug / Jade
  • LessCSS
  • HTML5
  • WebSockets


Java app - Game

Source Code

The game 2048 (created by Gabriele Cirulli) is so fun that my kids wanted their own copy. So I wrote this version in Java 8, using JavaFx for attractive graphics and silky smooth animations.

  • Java 8
  • JavaFx
  • Modular code
  • Customizable
  • Animations


macOS app - Window Manager

Source Code

I created this app to increase my productivity by letting me move windows around in macOS using keyboard shortcuts. It grew into a community-driven highly extensible app, using Lua for its plugin system.

  • Objective-C
  • Embedded Lua
  • Plugin system
  • Fully documented
  • 5,000 GitHub stars

Website - Social Network

Implementing this elite social network gave me experience integrating both Apple Pay and credit card payments (via seamlessly into web apps, for a frictionless and pain-free payment experience.

  • Clojure
  • Elastic Beanstalk
  • PostgreSQL
  • Apple Pay


Website - Live Chatroom

Source Code

This isn't just any chatroom. In this web app, you can see what everyone is typing while they type it. I made this in order to scratch my itch for making real-time apps and games, and learned how to use WebSockets in the process.

  • JavaScript
  • WebSockets
  • Node.js
  • Vue.js
  • CSS


macOS app - Music Player

Source Code

As iTunes went through many user interface changes, I wanted an app that was consistent, intuitive, and easy to use. So I created Bahamut, a minimal music player for macOS with a custom user interface.

  • Objective-C
  • Custom UI
  • Cocoa
  • Core Data
  • AVFoundation


macOS app - Chat (IRC) Client

Source Code

This was written in 2009, before the time of Slack, when IRC was the main way for programmers to get short-term assistance from each other. Its purpose was to be a beautiful app with an emphasis on simplicity and usability over technical power.

  • Async networking
  • Core Animation
  • Core Text
  • IRC Protocol
  • UI Design


macOS app - Window Manager

Source Code

This is an app I actually use every single day. It lets you move windows with global keyboard shortcuts. Since it uses Vim-like key bindings, it should feel pretty natural to any programmer. There's no configuration needed; it Just Works™.

  • Minimalist UI
  • Simple UI
  • Vim-like Hotkeys
  • Global Hotkeys
  • Zero-configuration


macOS app - Lua window manager

Source Code

As an evolution of Phoenix, Hydra was my first attempt at embedding a full Lua virtual machine into an Objective-C app, to make a lightweight and efficient window manager that focused on speed, low memory usage, low CPU usage, and overall being gentle on laptop batteries.

  • Embedded Lua
  • Generated docs
  • Lightweight
  • Memory efficient
  • CPU efficient


macOS app - JavaScript window manager

Source Code

As an evolution of Zephyros, Phoenix was my attempt to use Cocoa's native JavaScript bindings to make a more lightweight and efficient window manager, that focused on speed, low memory usage, low CPU usage, and overall being gentle on laptop batteries.

  • JavaScriptCore
  • JavaScript API
  • Lightweight
  • Memory efficient
  • CPU efficient

Smaller projects

These may be tiny, but they're interesting technical feats.

Lua4Swift Swift framework for embedding Lua with a native Swift API.
choose Command line fuzzy-matching tool for macOS that uses a GUI
music Command line music daemon for macOS that only speaks JSON
hecto Command line text editor with an embedded Lua plugin system
ZephSharp Window manager for Windows using Clojure for scripting
management Minimalist EC2 configuration & deployment tool in Ruby.
go.assert Assertion helper package for writing tests in Go.
go.shattr Go library for printing shell-attributed strings to stdout.
OCDSpec2 Objective-C based testing framework with Xcode integration.