A beginner's guide to Ruby blocks. It might be a bit hard to follow w/o the talk to go along with it. From April 2007

1. blocks
Lachs Cox
11th April

2. block, aka
closure lambda
proc
anonymous first-class
function function

3. Ruby
<3s
Blocks

4. 1. Reiterating the
Wisdom of
Blocking

5. canonical use:
iterator
(cliché?)

6. Do something
with each element
of an Array

7. an_array.each do |e|
something
end

8. index = 0
['hello', 'world!'].each do |word|
puts quot;#{index += 1} #{word}quot;
end

9. # >> 1 hello
# >> 2 world!

10. a block!
index = 0
['hello', 'world!'].each do |word|
puts quot;#{index += 1} #{word}quot;
end

11. code container

12. code
index = 0
['hello', 'world!'].each do |word|
puts quot;#{index += 1} #{word}quot;
end

13. block arguments
index = 0
['hello', 'world!'].each do |word|
puts quot;#{index += 1} #{word}quot;
end

14. iterator = Proc.new do...end
tangible
(carry it in your pocket)

15. iterator = Proc.new do...end
portable
(carry it in your pocket)

16. refactor
index = 0
iterator = Proc.new do |word|
puts quot;#{index += 1} #{word}quot;
end
['hello', 'world!'].each(&iterator)

17. refactor
index = 0
iterator = Proc.new do |word|
special
syntax
puts quot;#{index += 1} #{word}quot;
end
['hello', 'world!'].each(&iterator)

18. remembers
(its own state)

19. remembers
(its own state)
(binding to creation context)

20. binding
index = 0
['hello', 'world!'].each do |word|
puts quot;#{index += 1} #{word}quot;
end

21. self local vars
['hello', 'world!'].each do |word|
puts quot;#{index += 1} #{word}quot;
end

22. block
return
arguments code
value
binding

25. a block:
a portable code container
which remembers its state
and creation context.

26. pssst...!
for word in words
puts word
end
words.each do |word|
puts word
end

27. equivalent
for word in words
puts word
end
words.each do |word|
puts word
identical
end

28. pssst...!
binding

29. pssst...!
Kernel#binding
binding
(use it for evil)

30. 2. TMTOWTDI

31. style
array.each {|word| puts word}
array.each do |word|
puts word
index += 1
end

32. Basics
+
Syntax sugar.

33. Proc#new
Kernel#proc
Kernel#lambda

34. block = Proc.new do |action|
puts quot;#{self} #{action}s #{beer}quot;
end

35. block = lambda do |action|
puts quot;#{self} #{action}s #{beer}quot;
end

36. Syntax sugar.
(the real power)

37. def perform_action(action,block)
block.call(action)
end
beer = quot;beez neezquot;
block = lambda do |action|
puts quot;#{self} #{action}s #{beer}quot;
end
perform_action(:drink,block)
# >> main drinks beez neez

38. def perform_action(action)
yield action
end
beer = quot;beez neezquot;
perform_action(:drink) do |action|
puts quot;#{self} #{action}s #{beer}quot;
end
# >> main drinks beez neez

39. def perform_action(action,block)
block.call(action)
end

40. def perform_action(action,&block)
yield action if block_given?
end

41. def perform_action(action)
yield action if block_given?
end

42. def perform_action(action)
yield action
end

43. &
captures implicit
blocks

44. &
def foo(...,&block)
last arg

45. &
def foo(...,&block)
last arg
only one per method

46. def foo(&block)
block.class # => Proc, Proc, Proc
block.arity # => -1, 0, 1
end
foo { nil }
foo { || nil }
foo { |a| nil }

47. nuances
go here

48. argument pattern matching
perform_action([:drink,:eat,:be_merry]) do |(a,*b)|
a # => :drink
b # => [:eat, :be_merry]
end
perform_action([:ignore,:regard]) do |(_,a)|
a # => :regard
end

49. 3. The Building
Blocks of a
Perfect Meal

50. Roll your own
Enumerable

51. Roll your own
Enumerable
you implement each(&block)

52. Roll your own
Enumerable
you implement each(&block)
def each(&block)
(Hpricot(open(url)) / quot;aquot;)
.map {|a| a['href']}
.each(&block)
end

53. Roll your own
Enumerable
you implement each(&block)
def each(&block)
@brewery_visitor.rewind
while brewery = @brewery_visitor.next
yield brewery
end
end

54. Roll your own
Enumerable
include Enumerable

55. Roll your own
Enumerable
include Enumerable
you get
all?, any?, collect, detect, each_cons, each_slice,
each_with_index, entries, enum_cons, enum_slice,
enum_with_index, find, find_all, grep, include?,
inject, map, max, member?, min, partition, reject,
select, sort, sort_by, to_a, to_set, zip

56. Customised Behaviour
& Callbacks
class BeerController < ApplicationController
append_before_filter do
@beer = Beer.find(params[:id])
end
end

57. Refactoring
Ideas

58. Refactoring
Ideas
mixin module

59. Refactoring
Ideas
mixin module
extract subclass

60. Refactoring
Ideas
mixin module
extract subclass
template pattern

61. Refactoring
Ideas
mixin module
extract subclass
template pattern
logic blocks

62. bonus 1
4. Yielding Secrets
of Erb

63. def __render_...(local_vars)
# copy local vars
template
template
Erb code
rhtml
String
end
render
eval template
method

64. send(:__render..., local_assigns) do |*name|
instance_variable_get quot;@content_for_#{name.first || 'layout'}quot;
end
<%= yield %> # => @content_for_layout
<%= yield :clean %> # => @content_for_clean
<%= yield :clean, :dirty %> # => @content_for_clean

65. bonus 2
5. An Empirical
Approach Using
Text–mate

66. +
xmpfilter by mfp
http://eigenclass.org/hiki/rcodetools

67. explore
[:a,:b,:c].each do |c|
c
puts c
end

68. explore
[:a,:b,:c].each do |c|
c # =>
puts c # =>
end

69. #⇥
# =>

70. Execute and Update ‘# =>’ Markers
⌃⇧⌘E

71. explore
[:a,:b,:c].each do |c|
c # => :a, :b, :c
puts c # => nil, nil, nil
end
# >> a
# >> b
# >> c