These are my notes for planning the talk.

Vague Ideas/Notes

Why would anyone care what I have to say on the topic? => Background
Build up a C extension through the talk
What are C extensions good for?
What are C extensions NOT good for?
Under what circumstances can you even use a C extension?
Make sure to point out the Ruby cross reference
The pick-axe has a whole chapter on this: http://media.pragprog.com/titles/ruby3/ext_ruby.pdf
Readme from the source https://github.com/ruby/ruby/blob/trunk/README.EXT
Gotchas

Rough outline

Introduction
Background/Self-history (What have I used C extensions for)
When (not) to use C extensions
- Use C for raw performance
  - Specialized string processing
  - When you do the same specialized operation over and over again and can therefore optimize it to death
  - Handling huge data structures
  - Raw access to binary data
  - Numerical processing
- Use C to bridge with existing C/C++ libraries
- Don't use C to do something your Ruby implementation already does really well
  - Don't rewrite MRI
  - If you're thinking about rewriting Rack in C, you're gonna have a bad time. (Rethink your architecture.)
  - Don't "C Extension all of the things!"
Compatibility concerns/Gotchas
- The API was developed for MRI ("standard" Ruby)
- Should be mostly compatible with C/C++-based VMs, though you may experience hiccups
- Notably does NOT work with JRuby
- The API is strictly in C, but can be used with C++ code
- You lose some speed at the interface (as well as code manageability)
Basic procedure - 10,000 foot view
- Create your c source
  - Actual algorithm
  - Interface layer
- Create an 'extconf.rb' => ruby extconf.rb creates a Makefile
- Make => Creates 'your-extension.bundle' (RbConfig::CONFIG['DLEXT'])
- require 'your-extension'
- (Optional) Create a wrapper class in Ruby
Create the c source (basics)
- Interface layer
- Convert to/from Ruby data structures
Build and use
- extconf.rb
- make
- require
- wrappers (C and Ruby in the same class)