OOP, metaprogramming, blocks, iterators

Anton Shemerey
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Code style
https://github.com/bbatsov/ruby-style-guide
https://github.com/bbatsov/rails-style-guide
Use two spaces per tab!
explicit “return” - is evil

OOP - Everything is object, not quite but still...

“hello” - this is object too
1
2 a = "hello" # instance
3 b = a.dup # new object
4
5 # instance method (for object)
6 class << a
7 def to_s
8 "#{self} world"
9 end
10
11 def say_hello
12 self.to_s
13 end
14 end
15
16 a.to_s # => "hello world"
17 b.to_s # => "hello"
18 a.methods - b.methods # => [:say_hello]
19 a.class.methods - b.class.methods # => []
1
2 def a.to_s
3 "#{self} world"
4 end
5
6 def a.say_hello
7 self.to_s
8 end
9

42 - this is object too
42.instance_variables # => []
42.instance_variable_set(:@hello, 'world')
42.instance_variables # => [:@hello]
42.object_id # => 85

true - this is object too
true.instance_variables # => []
true.instance_variable_set(:@false, true)
true.instance_variables # => [:@false
true.object_id # => 2
false.object_id # => 0
nil.object_id # => 4

Class
3 class Point
4 def initialize(x, y)
5 @x, @y = x, y
6 end
7 end
8
9 if __FILE__ == $PROGRAM_NAME
10 puts Point.new(1, 10).inspect #
11 end

attribute reader/writer
1 class Point
2 def initialize(x)
3 @x = x
4 end
5
6 def x
7 @x
8 end
9
10 def x=(x)
11 @x = x
12 end
13 end
14
1 class Point
2 attr_accessor :x
3
4 def initialize(x)
5 @x = x
6 end
7 end
8

1 module ReadWrite
2 def rw(*params) # params = [:x, :y] 3 params.each do |attr|
4 define_method attr do # def x
5 instance_variable_get :"@#{attr}" # @x
6 end # end
7
8 define_method :"#{attr}=(val)" do # def x=(val)
9 instance_variable_set :"@#{attr}=", val # @x=val
10 end # end
11 end
12 end
13 end
14
15 class Object
16 extend ReadWrite
17 end
18
19 class Point
20 rw :x, :y
21
22 def initialize(x)
23 @x = x
24 end
25 end
26

Class / Module
Module.ancestors
# => [Module, Object, Kernel, BasicObject]
Class.ancestors
# => [Class, Module, Object, Kernel, BasicObject]

class A; end
new
inheritance
include class A - computer says no
extend class A - computer says no
computer says no - http://bit.ly/gQX24

module B; end
new - computer says no
inheritance - computer says no
include B
extend B
computer says no - http://bit.ly/gQX24

include/extend
1 module M
2 def inst_method
3 "instance"
4 end
5 end
6
7
8 class Point
9 include M
10 end
11
12 if __FILE__ == $PROGRAM_NAME
13 puts Point.new.inst_method
14 end
15
1 module M
2 def cl_method
3 "instance"
4 end
5 end
6
7
8 class Point
9 extend M
10 end
11
12 if __FILE__ == $PROGRAM_NAME
13 puts Point.cl_method
14 end
15

1 module M
2 def self.included(base)
3 base.extend(ClassMethods)
4 end
5
6 # -- instance methods --
7
8 module ClassMethods
9 # -- class methods --
10 end
11 end
12
13
14 class Point
15 include M
16
17 def initialize(x)
18 @x = x
19 end
20 end

Classes and Objects
More information: http://bit.ly/YZBfmp

Ruby Blocks
1 %w[first second third].each do |item|
2 item.capitalize
3 end
4
5 %w[first second third].each { |i| i.upcase }
6
7 %w[first second third].each <<= block

Yield

1 require "ostruct"
2 Point = Struct.new(:x, :y)
3
4 class PointList
5 def initialize
6 @data = []
7 end
8
9 def <<(other)
10 @data << other
11 end
12
13 def each
14 for item in @data
15 yield item <<<<<<<<<<<<
16 end
17 end
18 end
19
20 if __FILE__ == $PROGRAM_NAME
21 list = PointList.new << Point.new(1,3) << Point.new(2,1)
22 list.each do |point|
23 puts point #
, #
24 end
25 end
13 def each(&block)
14 for item in @data
15 block.call(item)
16 end
17 end
13 def each(block = Proc.new)
14 for item in @data
15 block.call(item)
16 end
17 end

Enumerable

1 require "ostruct"
2
3 Point = Struct.new(:x, :y) do 4 def distance
5 Math.sqrt(x**2 + y**2)
6 end
7 end
8
9 class PointList
include Enumerable <<<<<<<
10 # -- code omitted --
11
12 def each
13 for item in @data
14 yield item
15 end
16 end
17 end
18
19 if __FILE__ == $PROGRAM_NAME
20 list = PointList.new << Point.new(1,3) << Point.new(2,1) << Point.new(2,2)
21 list.sort_by(&:distance)
22 list.sort_by {|e| e.distance }
23 end
http://ru.wikibooks.org/wiki/Ruby/Справочник/Enumerable

Comparable
<=>
1, 0, -1

1 require "ostruct"
2
3 Point = Struct.new(:x, :y) do 4 include Comparable <<<<<<
5
6 def distance
7 Math.sqrt(x**2 + y**2)
8 end
9
10 def <=>(other)
11 self.distance <=> other.distance
12 end
13 end
14
15 if __FILE__ == $PROGRAM_NAME
16 puts Point.new(1,3) == Point.new(2,1) # false
17 puts Point.new(1,3) == Point.new(3,1) # true
18 puts Point.new(2,3) >= Point.new(1,1) # true
19 puts Point.new(2,3) <= Point.new(1,1) # false
20 puts Point.new(2,2).between? Point.new(2,1), Point.new(2,3) #true
21 end
Comparable

Mad Ruby

#to_proc (&)
1 class Symbol
2 def to_proc
3 Proc.new { |*args| args.shift.__send__(self, *args) }
4 end
5 end
19 if __FILE__ == $PROGRAM_NAME
20 list = PointList.new << Point.new(1,3) << Point.new(2,1) << Point.new(2,2)
21 list.sort_by(&:distance)
22 list.sort_by {|e| e.distance }
23 end
1 [1, 2, 3].map(&:to_s) # => ["1", "2", "3"]
2 [3, 4, 5].inject(&:*) # => 60

Advanced Examples
1 File.open('nginx.log', 'r') do |file|
2 while line = file.gets 3 puts line
4 end
5 end
6
7 # -- possible implementation --
8 class File
9 def open(file, option)
10 if block_given?
11 f = fopen(file, option)
12 yield f
13 f.close
14 end
15 end
16 end
1 ActiveRecord::Base.transaction do
2 # -- code omitted --
3 end
4
5 # -- possible implementation --
6 module ActiveRecord
7 class Base
8 def transaction
9 # -- start transaction
10 yield
11 # -- commit transaction
12 rescue ActiveRecord::Rollback
13 # -- roll back transaction
14 ensure
15 # -- close transaction
16 end
17 end
18 end