Ruby: OOP, metaprogramming, blocks, iterators, mix-ins, duck typing. Code style

OOP,
metaprogramming,
blocks, iterators, mix-
ins, duck typing.
Code style
Code style

Anton Shemerey
• https://github.com/shemerey
• https://twitter.com/shemerey
• https://www.facebook.com/shemerey
• https://www.linkedin.com/in/shemerey
• shemerey@gmail.com
• etc.

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
1
7 def to_s
2 def a.to_s
8 "#{self} world"
3 "#{self} world"
9 end
4 end
10
5
11 def say_hello
6 def a.say_hello
12 self.to_s
7 self.to_s
13 end
8 end
14 end
9
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 # => []

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 #<Point:0x0bf78 @x=1, @y=10>
11 end

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

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

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

http://ru.wikibooks.org/wiki/Ruby/Справочник/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
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

Comparable
<=>
1, 0, -1
1, 0, -1
1, 0, -1

Comparable
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
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

#to_proc (&)
1 class Symbol
2 def to_proc
3 Proc.new { |*args| args.shift.__send__(self, *args) }
4 end
5 end

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

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