If you've ever looked into how to create Gems, you've probably seen a bunch of ways to do that. Project generators like Hoe, Jeweler, and the like offer some nice ways to get started, but they may often be overkill for many projects. If you're just starting out, why not learn to do it from scratch? In this talk, we'll create our own gem from scratch, using only things that are provided by Ruby, its standard library, and RubyGems to craft a simple gem. You'll learn how to set up a project, how to write and run tests, how to use Rake to quickly build the gem, and even how to create a gem that installs an executable command-line program.

1. Building A Gem From
Scratch
Madison Ruby, 2011
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email: brianhogan at napcs.com

2. What's A Gem?
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email: brianhogan at napcs.com

3. The (normal) Process
• Come up with an idea
• write some code
• Release a gem
• Beg people to write tests for you
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email: brianhogan at napcs.com

4. Our process
• Come up with an idea and write some code
• Throw all that code away
• Rewrite it with tests as we go
• Release it as a Gem
• Enjoy fame and fortune
twitter: bphogan
email: brianhogan at napcs.com

5. Grabatar
(a gem to grab Gravatar URLs)
http://www.gravatar.com/avatar/
6ef8cb7cd7cd58077f0b57e4fa49a969
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email: brianhogan at napcs.com

6. Step one: Build tested,
working code
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email: brianhogan at napcs.com

7. The basic structure of a
Gem
gemname.gemspec
lib/
gemname
version.rb
anotherfile.rb
gemname.rb
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email: brianhogan at napcs.com

8. Tests, Tests, Tests!
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email: brianhogan at napcs.com

9. Test::Unit
test
somefile_test.rb
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email: brianhogan at napcs.com

10. Write the test
test/grabatar_test.rb
require 'test/unit'
require 'lib/grabatar'
class GrabatarTest < Test::Unit::TestCase
def test_displays_version
assert Grabatar::VERSION
end
end
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email: brianhogan at napcs.com

11. Implement the code
lib/grabatar/version.rb
module Grabatar
VERSION = "0.0.2"
end
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email: brianhogan at napcs.com

12. Add to the main Ruby file:
lib/grabatar.rb
require 'grabatar/version'
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email: brianhogan at napcs.com

13. Repeat.
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email: brianhogan at napcs.com

14. Write the test first...
test/gravatar_helper.rb
require 'test/unit'
require 'grabatar'
class GravatarTest < Test::Unit::TestCase
def test_builds_gravatar_url
g = Grabatar::Gravatar.new("bphogan@gmail.com")
assert_equal "http://www.gravatar.com/avatar/
6ef8cb7cd7cd58077f0b57e4fa49a969", g.avatar_url
end
end
twitter: bphogan
email: brianhogan at napcs.com

15. Then write the code
lib/grabatar/gravatar.rb
module Grabatar
class Gravatar
require 'digest/md5'
def initialize(email)
@email = email
end
def avatar_url
hash = Digest::MD5.hexdigest(@email)
"http://www.gravatar.com/avatar/#{hash}"
end
end
end
twitter: bphogan
email: brianhogan at napcs.com

16. Then write the code
lib/grabatar/gravatar.rb
module Grabatar
class Gravatar
require 'digest/md5'
def initialize(email)
@email = email
end
def avatar_url
hash = Digest::MD5.hexdigest(@email)
"http://www.gravatar.com/avatar/#{hash}"
end
end
end
twitter: bphogan
email: brianhogan at napcs.com

17. Then write the code
lib/grabatar/gravatar.rb
module Grabatar
class Gravatar
require 'digest/md5'
def initialize(email)
@email = email
end
def avatar_url
hash = Digest::MD5.hexdigest(@email)
"http://www.gravatar.com/avatar/#{hash}"
end
end
end
twitter: bphogan
email: brianhogan at napcs.com

18. Then write the code
lib/grabatar/gravatar.rb
module Grabatar
class Gravatar
require 'digest/md5'
def initialize(email)
@email = email
end
def avatar_url
hash = Digest::MD5.hexdigest(@email)
"http://www.gravatar.com/avatar/#{hash}"
end
end
end
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email: brianhogan at napcs.com

19. Step two: Make A
Gemspec
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email: brianhogan at napcs.com

20. Gemspecs are easy.
grabatar.gemspec
require 'lib/grabatar/version'
Gem::Specification.new do |s|
s.name = "grabatar"
s.version = Grabatar::VERSION
s.summary = "Fetch avatar image URLs from Gravatar"
s.authors = ["Brian Hogan"]
s.email = ["bphogan@gmail.com"]
s.files = [
"lib/grabatar.rb",
"lib/grabatar/version.rb",
"lib/grabatar/gravatar.rb",
"lib/grabatar/railtie.rb",
"lib/grabatar/view_helpers.rb"
]
end
twitter: bphogan
email: brianhogan at napcs.com

21. Gemspecs are easy.
grabatar.gemspec
require 'lib/grabatar/version'
Gem::Specification.new do |s|
s.name = "grabatar"
s.version = Grabatar::VERSION
s.summary = "Fetch avatar image URLs from Gravatar"
s.authors = ["Brian Hogan"]
s.email = ["bphogan@gmail.com"]
s.files = [
"lib/grabatar.rb",
"lib/grabatar/version.rb",
"lib/grabatar/gravatar.rb",
"lib/grabatar/railtie.rb",
"lib/grabatar/view_helpers.rb"
]
end
twitter: bphogan
email: brianhogan at napcs.com

22. Gemspecs are easy.
grabatar.gemspec
require 'lib/grabatar/version'
Gem::Specification.new do |s|
s.name = "grabatar"
s.version = Grabatar::VERSION
s.summary = "Fetch avatar image URLs from Gravatar"
s.authors = ["Brian Hogan"]
s.email = ["bphogan@gmail.com"]
s.files = [
"lib/grabatar.rb",
"lib/grabatar/version.rb",
"lib/grabatar/gravatar.rb",
"lib/grabatar/railtie.rb",
"lib/grabatar/view_helpers.rb"
]
end
twitter: bphogan
email: brianhogan at napcs.com

23. Gemspecs are easy.
grabatar.gemspec
require 'lib/grabatar/version'
Gem::Specification.new do |s|
s.name = "grabatar"
s.version = Grabatar::VERSION
s.summary = "Fetch avatar image URLs from Gravatar"
s.authors = ["Brian Hogan"]
s.email = ["bphogan@gmail.com"]
s.files = [
"lib/grabatar.rb",
"lib/grabatar/version.rb",
"lib/grabatar/gravatar.rb",
"lib/grabatar/railtie.rb",
"lib/grabatar/view_helpers.rb"
]
end
twitter: bphogan
email: brianhogan at napcs.com

24. The manifest
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email: brianhogan at napcs.com

25. bundle gem is bad for you
s.files = `git ls-files`.split("n")
s.test_files = `git ls-files --
{test,spec,features}/*`.split("n")
s.executables = `git ls-files -- bin/*`
.split("n").map{ |f| File.basename(f) }
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email: brianhogan at napcs.com

26. What lies beneath
• .DS_Store
• thumbs.db
• ~whatever.rb
• whatever.mine.rb
• Step 3: Rake
• Test::Unit tasks
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email: brianhogan at napcs.com

27. Craft your manifest by hand
s.files = [
"lib/grabatar.rb",
"lib/grabatar/version.rb",
"lib/grabatar/gravatar.rb",
"lib/grabatar/railtie.rb",
"lib/grabatar/view_helpers.rb"
]
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email: brianhogan at napcs.com

28. Build and install the gem
$ gem build grabatar.gemspec
$ gem install grabatar-0-0-1.gem
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email: brianhogan at napcs.com

29. Step 4: Rails gems
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30. Test first
test/view_helpers_test.rb
require 'test/unit'
require 'grabatar/gravatar'
require 'grabatar/view_helpers'
class ViewHelpers < Test::Unit::TestCase
include Grabatar::ViewHelpers
def test_generates_avatar_url
assert_equal
"http://www.gravatar.com/avatar
/6ef8cb7cd7cd58077f0b57e4fa49a969",
gravatar_url_for("bphogan@gmail.com")
end
end
twitter: bphogan
email: brianhogan at napcs.com

31. Test first
test/view_helpers_test.rb
require 'test/unit'
require 'grabatar/gravatar'
require 'grabatar/view_helpers'
class ViewHelpers < Test::Unit::TestCase
include Grabatar::ViewHelpers
def test_generates_avatar_url
assert_equal
"http://www.gravatar.com/avatar
/6ef8cb7cd7cd58077f0b57e4fa49a969",
gravatar_url_for("bphogan@gmail.com")
end
end
twitter: bphogan
email: brianhogan at napcs.com

32. Create a helper
lib/grabatar/view_helpers.rb
module Grabatar
module ViewHelpers
def gravatar_url_for(email)
Grabatar::Gravatar.new(email).avatar_url
end
end
end
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email: brianhogan at napcs.com

33. Railties
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email: brianhogan at napcs.com

34. Include the Helper
lib/grabatar/railtie.rb
module Grabatar
class Railtie < Rails::Railtie
initializer "grabatar.view_helpers" do
ActionView::Base.send :include, ViewHelpers
end
end
end
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email: brianhogan at napcs.com

35. Only load the Railtie if we have Rails
lib/grabatar.rb
require 'grabatar/railtie' if defined?(Rails)
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email: brianhogan at napcs.com

36. Making a CLI tool
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37. Add a bin folder with
the file!
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email: brianhogan at napcs.com

38. The CLI program
bin/grabatar
#!/usr/bin/env ruby
require 'grabatar'
puts "Grabatar v#{Grabatar::VERSION}"
email = ARGV[0]
if email.nil?
puts "Usage: grabatar <youremail@server.com>"
else
g = Grabatar::Gravatar.new(email)
puts g.avatar_url
end
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email: brianhogan at napcs.com

39. The CLI program
bin/grabatar
#!/usr/bin/env ruby
require 'grabatar'
puts "Grabatar v#{Grabatar::VERSION}"
email = ARGV[0]
if email.nil?
puts "Usage: grabatar <youremail@server.com>"
else
g = Grabatar::Gravatar.new(email)
puts g.avatar_url
end
twitter: bphogan
email: brianhogan at napcs.com

40. The CLI program
bin/grabatar
#!/usr/bin/env ruby
require 'grabatar'
puts "Grabatar v#{Grabatar::VERSION}"
email = ARGV[0]
if email.nil?
puts "Usage: grabatar <youremail@server.com>"
else
g = Grabatar::Gravatar.new(email)
puts g.avatar_url
end
twitter: bphogan
email: brianhogan at napcs.com

41. Running it
$ grabatar bphogan@gmail.com
Grabatar v0.0.2
http://www.gravatar.com/avatar/6ef8cb7cd7cd58077f0b57e4fa49a969
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email: brianhogan at napcs.com

42. Who wants code?
http://github.com/napcs/grabatar
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email: brianhogan at napcs.com

43. Thanks!
http://spkr8.com/t/8181
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email: brianhogan at napcs.com