argument_lookup.rb

RUBY_VERSION #=> "2.1.2"
def foo; 123 end
def bar(foo = foo)
  p foo       # => 123
  p foo.class # => Fixnum
end

# Ruby2.2からは警告を出した上で、nilが代入されるようになる
RUBY_VERSION #=> "2.2.0"
def foo; 123 end
def bar(foo = foo)
  p foo       # => nil
  p foo.class # => NilClass
end
# => warning: circular argument reference - foo

argument_lookup_method_call.rb

RUBY_VERSION #=> "2.2.0"
def foo; 123 end
# 以前と同じ挙動をさせたい場合はメソッド呼び出しであることを明確にするため()を付ける
def bar(foo = foo())
  p foo       # => 123
  p foo.class # => Fixnum
end

assign_undefined.rb

# メソッド引数以外では以前からこの動作
RUBY_VERSION #=> "2.1.2"
x     #=> NameError: undefined local variable or method `x' for main:Object
x = x #=> nil
x     #=> nil

RUBY_VERSION #=> "2.2.0"
x     #=> NameError: undefined local variable or method `x' for main:Object
x = x #=> nil
x     #=> nil

binding_basic.rb

RUBY_VERSION #=> "2.1.2"
a = 1
bnd = binding #=> #<Binding:0x007fdaab3f3788>
bnd.eval('local_variables') #=> [:bnd, :a, ...]
bnd.local_variables         #=> NoMethodError: private method `local_variables' called for #<Binding:0x007fdaab3f3788>


RUBY_VERSION #=> "2.2.0"
a = 1
bnd = binding #=> #<Binding:0x007f99ce089b88>
bnd.eval('local_variables') #=> [:bnd, :a, ...]
bnd.local_variables         #=> [:bnd, :a, ...]

birthtime.rb

RUBY_VERSION #=> 2.2.0

p File.open('local_variables.rb').birthtime
# => 2015-02-20 07:29:10 +0900

p File.open('local_variables.rb').ctime

# File#mtimeは最終更新時間を返す
p File.open('local_variables.rb').mtime
# => 2015-02-21 01:26:17 +0900

curry.rb

def mul(a, b)
  a * b
end

# メソッドオブジェクトを取得
m = method(:mul) #=> #<Method: Object#mul>

# Methodをcurry化するとProcになります
p prc = m.curry #=> #<Proc:0x007fe0fa08a6c8 (lambda)>

# カリー化されたprocに対して、引数の部分適用が可能になります
p mul10 = prc.call(10) #=> #<Proc:0x007fea15885e08 (lambda)>

# のこりひとつの引数を適用します
p mul10.call(21) #=> 210

# ちなみに.call(xxx)は.(xxx)とも書けます
p mul10.(21)

float.rb

p 2.0.next_float #=> 2.0000000000000004
p 2.0.prev_float #=> 1.9999999999999998

frozen.rb

RUBY_VERSION # => 2.1.2
[true, false, nil].map(&:frozen?)
=> [false, false, false]

RUBY_VERSION # => 2.2.0
[true, false, nil].map(&:frozen?)
=> [true, true, true]

hash_literal.rb

RUBY_VERSION #=> 2.1.2

{ "super-key": 1, "hyper-key": 2 }
# => SyntaxError: unexpected ':', expecting =>
#    { "super-key": 1, "hyper-key": 2 }
#                  ^

# こう書く必要があった
{ :"super-key" => 1, :"hyper-key" => 2 }
# => {:"super-key"=>1, :"hyper-key"=>2}


RUBY_VERSION #=> 2.2.0
{ "super-key": 1, "hyper-key": 2 }
#=> {:"super-key"=>1, :"hyper-key"=>2}

itself.rb

ary = [2, 3, 0, 3, 4, 2, 4, 3, 0, 2]
ary.group_by(&:itself)
#=> {2=>[2, 2, 2], 3=>[3, 3, 3], 0=>[0, 0], 4=>[4, 4]}

# 2.1以前はitselfがないのでこう書くしかない
ary.group_by{|i| i }
#=> {2=>[2, 2, 2], 3=>[3, 3, 3], 0=>[0, 0], 4=>[4, 4]}

lambda_arguments.rb

RUBY_VERSION #=> 2.1.2
lam = ->(word, index) { word.length == 3 }
#=> #<Proc:0x007fe112b26ba0@(pry):27 (lambda)>
%w(Hi there how are you).each_with_index.detect &lam
#=> ArgumentError: wrong number of arguments (1 for 2)

RUBY_VERSION #=> 2.2.0
lam = ->(word, index) { word.length == 3 }
#=> #<Proc:0x007f856e44cb90@(pry):70 (lambda)>
%w(Hi there how are you).each_with_index.detect &lam
#=> ["how", 2]

local_variables.rb

a = 1
b = 2

RUBY_VERSION # => 2.1.2
local_variables # => [:a, :b]
binding.eval('local_variables') # => [:a, :b]
binding.local_variables
# => NoMethodError: private method `local_variables' called for #<Binding:0x007fe1133b8548>

RUBY_VERSION # => 2.2.0
local_variables # => [:a, :b]
binding.eval('local_variables') # => [:a, :b]
binding.local_variables # => [:a, :b]

log.rb

RUBY_VERSION #=> "2.2.0"

p Math.log(2.7)   #=> 0.9932517730102834
p Math.log(2.8)   #=> 1.0296194171811581
p Math.log(10, 2) #=> 3.3219280948873626

p Math.log(10, -2)
#=> Numerical argument is out of domain - "log" (Math::DomainError)

math_log.rb

RUBY_VERSION #=> 2.1.2
Math.log(Math::E, -2) #=> NaN

RUBY_VERSION #=> 2.2.0
Math.log(Math::E, -2)
#=> Math::DomainError: Numerical argument is out of domain - "log"

max.rb

[2, 5, 3, 4, 1].max    #=> 5
[2, 5, 3, 4, 1].max(3) #=> [5, 4, 3]

receiver.rb

RUBY_VERSION # => 2.1.2
binding.eval('self') # => main
binding.receiver
#=> NoMethodError: undefined method `receiver' for #<Binding:0x007fe1159032f8>

RUBY_VERSION # => 2.2.0
binding.eval('self') # => main
binding.receiver # => main

slice_after.rb

p [1, 3, :a, 4, 5, 6].slice_before{|e| e.is_a? Symbol}.to_a
#=> [[1, 3], [:a, 4, 5, 6]]

p [1, 3, :a, 4, 5, 6].slice_after{|e| e.is_a? Symbol}.to_a
#=> [[1, 3, :a], [4, 5, 6]]

# ブロックの中身がis_aならクラスを受け取って次のように書いても同じ
[1, 3, :a, 4, 5, 6].slice_after(Symbol).to_a

# slice_when
p [1, 3, 4, 5, 6, 8, 10, 12].slice_when{|e| e.odd? }.to_a
#=> [[1], [3], [4, 5], [6, 8, 10, 12]]

# 比較もできる. 値が2以上ジャンプしたところでsliceする例
p [1, 3, 4, 5, 6, 8, 10, 12].slice_when{|e1, e2| e1 + 1 < e2 }.to_a
#=> [[1], [3, 4, 5, 6], [8], [10], [12]]