codewithbehnam/cc-docs/andrew-kane-gem-writer

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This skill should be used when writing Ruby gems following Andrew Kane's proven patterns and philosophy. It applies when creating new Ruby gems, refactoring existing gems, designing gem APIs, or when clean, minimal, production-ready Ruby library code is needed. Triggers on requests like "create a gem", "write a Ruby library", "design a gem API", or mentions of Andrew Kane's style.

Install

npx vskill@latest install codewithbehnam/cc-docs/andrew-kane-gem-writer

SKILL.md

The same SKILL.md was published earlier as mikker/dotfiles/andrew-kane-gem-writer.

Andrew Kane Gem Writer

Write Ruby gems following Andrew Kane's battle-tested patterns from 100+ gems with 374M+ downloads (Searchkick, PgHero, Chartkick, Strong Migrations, Lockbox, Ahoy, Blazer, Groupdate, Neighbor, Blind Index).

Core Philosophy

Simplicity over cleverness. Zero or minimal dependencies. Explicit code over metaprogramming. Rails integration without Rails coupling. Every pattern serves production use cases.

Entry Point Structure

Every gem follows this exact pattern in lib/gemname.rb:

ruby
# 1. Dependencies (stdlib preferred)
require "forwardable"
# 2. Internal modules
require_relative "gemname/model"
require_relative "gemname/version"
# 3. Conditional Rails (CRITICAL - never require Rails directly)
require_relative "gemname/railtie" if defined?(Rails)
# 4. Module with config and errors
module GemName
class Error < StandardError; end
class InvalidConfigError < Error; end
class << self
attr_accessor :timeout, :logger
attr_writer :client
end
self.timeout = 10 # Defaults set immediately
end

Class Macro DSL Pattern

The signature Kane pattern—single method call configures everything:

ruby
# Usage
class Product < ApplicationRecord
searchkick word_start: [:name]
end
# Implementation
module GemName
module Model
def gemname(**options)
unknown = options.keys - KNOWN_KEYWORDS
raise ArgumentError, "unknown keywords: #{unknown.join(", ")}" if unknown.any?
mod = Module.new
mod.module_eval do
define_method :some_method do
# implementation
end unless method_defined?(:some_method)
end
include mod
class_eval do
cattr_reader :gemname_options, instance_reader: false
class_variable_set :@@gemname_options, options.dup
end
end
end
end

Rails Integration

Always use `ActiveSupport.on_load`—never require Rails gems directly:

ruby
# WRONG
require "active_record"
ActiveRecord::Base.include(MyGem::Model)
# CORRECT
ActiveSupport.on_load(:active_record) do
extend GemName::Model
end
# Use prepend for behavior modification
ActiveSupport.on_load(:active_record) do
ActiveRecord::Migration.prepend(GemName::Migration)
end

Configuration Pattern

Use class << self with attr_accessor, not Configuration objects:

ruby
module GemName
class << self
attr_accessor :timeout, :logger
attr_writer :master_key
end
def self.master_key
@master_key ||= ENV["GEMNAME_MASTER_KEY"]
end
self.timeout = 10
self.logger = nil
end

Error Handling

Simple hierarchy with informative messages:

ruby
module GemName
class Error < StandardError; end
class ConfigError < Error; end
class ValidationError < Error; end
end
# Validate early with ArgumentError
def initialize(key:)
raise ArgumentError, "Key must be 32 bytes" unless key&.bytesize == 32
end

Testing (Minitest Only)

ruby
# test/test_helper.rb
require "bundler/setup"
Bundler.require(:default)
require "minitest/autorun"
require "minitest/pride"
# test/model_test.rb
class ModelTest < Minitest::Test
def test_basic_functionality
assert_equal expected, actual
end
end

Gemspec Pattern

Zero runtime dependencies when possible:

ruby
Gem::Specification.new do |spec|
spec.name = "gemname"
spec.version = GemName::VERSION
spec.required_ruby_version = ">= 3.1"
spec.files = Dir["*.{md,txt}", "{lib}/**/*"]
spec.require_path = "lib"
# NO add_dependency lines - dev deps go in Gemfile
end

Anti-Patterns to Avoid

  • method_missing (use define_method instead)
  • Configuration objects (use class accessors)
  • @@class_variables (use class << self)
  • Requiring Rails gems directly
  • Many runtime dependencies
  • Committing Gemfile.lock in gems
  • RSpec (use Minitest)
  • Heavy DSLs (prefer explicit Ruby)

Reference Files

For deeper patterns, see:

  • [references/module-organization.md](references/module-organization.md) - Directory layouts, method decomposition
  • [references/rails-integration.md](references/rails-integration.md) - Railtie, Engine, on_load patterns
  • [references/database-adapters.md](references/database-adapters.md) - Multi-database support patterns
  • [references/testing-patterns.md](references/testing-patterns.md) - Multi-version testing, CI setup
  • [references/resources.md](references/resources.md) - Links to Kane's repos and articles

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