A few blog posts ago, I explained a technique I planned to use for catching parse errors.
When my parser encounters an error, the easiest way to abandon ship is to just throw an exception. That plan works fine when you’re using pure ObjC objects, since you can just autorelease the objects.
The problem is that I’m not using ObjC objects to store my parsing data. I’m using plain C structs, which turns out to be hecka fast. It can parse an average-sized file a few thousand times per second.
My old solution was to include a “dry-run” flag in the parser. It’ll only allocate and return real objects when this value is set to true. Then I’d parse the document twice: one as a dry-run, and if no exceptions were thrown, a second time to create a real AST.
The that solution was error-prone. You could easily forget to add an
if-statement when creating something. Plus it’s noisy to see
(!dry_run) all over the place. So I ditched that solution pretty
quickly, and just let it throw errors until I could think of a better
This morning I thought of one. The real problem was that I would lose
access to all the little
malloc‘d objects that happen inside the
parser. So I figured, why not just
malloc a giant chunk of memory at
the top of the parser, and pass it through? Then whether it finished
parsing or not, I could just free it at the end.
I also thought it would be way faster to allocate all that memory up-front instead. But to my surprise, it was basically the same speed. I think it saw a bigger speed increase when I switched away from CFString functions to just operating on C-strings in my lexer, although that was pretty negligible too.
So now my parser feels so much cleaner, and it doesn’t leak memory anymore. Huge win!
I’m also considering jumping out of the stack manually instead of abusing exceptions when I find a parse-error. I’d have to use an out-param to communicate the damage and the intention to wind back up the stack manually. That plan feels a bit fragile, since I’ll still need to remember to jump out at call-sites that may have jumped out.
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 firstname.lastname@example.org to set up a phone call.
- 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)
- REST APIs
- AWS / EC2 / ELB
- HTML5 / CSS
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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- 2017 — "Clean code" isn't actually clean
- 2017 — Passion in your field is overrated
- 2017 — What I learned in 5 days of writing an experimental website
- 2014 — Age of the Polyglot
- 2013 — How to Program
- 2013 — Ignore the Naysayers
- 2013 — Writing Clearly
- 2012 — Reinvent the wheel
- 2010 — Good usability
- 2009 — Twitter is the wrong tool
- 2009 — We're all pretty bad at driving
- 2008 — Why I Code
|August||NDD: Narrative Driven Development|
|August||The truth about TDD|
|August||Macroframeworks vs Microframeworks|
|March||Notes on Haskell Extensions|
|February||Second thoughts on front-end tools|
|February||First thoughts on front-end tools|
|February||Some thoughts on GUIs|
|February||First thoughts on OCaml|
|February||First thoughts on Haskell|
|August||Age of the Polyglot|
|August||The history of Mjolnir|
|August||Quitting the GUI wars|
|June||Lua: my new favorite extension language|
|January||My programming life-goals|
|January||Lingua Latina, Pars I|
|January||Allocating an AST on the stack|
|April||Ruby Accessors Considered Pernicious|
|March||Reinvent the wheel|
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.
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.
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.
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.
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.
Implementing this elite social network gave me experience integrating both Apple Pay and credit card payments (via Stripe.com) seamlessly into web apps, for a frictionless and pain-free payment experience.
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.
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.
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™.
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.
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.|