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
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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
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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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email: brianhogan at napcs.com

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