Ruby初心者の不思議な経験 ref: http://qiita.com/dulao5/items/5bf55262aac6446e719e

file0.rb

print("abc") # print "abc" and return nil
print "abc"  # print "abc" and return nil 
print() # print "" and return nil 

print   # print "" and return nil 
        # 括弧がなくてもprint()と同じで、print関数の値を取れません

method(:print) # => #<Method: Object(Kernel)#print>

file1.rb

{a:1, b:2}.map.with_index do |(key,value), index| "#{index} : #{key} => #{value}" end
# => ["0 : a => 1", "1 : b => 2"]

file10.rb

class MyBase
  def foo()
    p 'MyBase::foo'
  end
end

class MyTest < MyBase
  def helpers(&proc)
    self.class.class_eval(&proc) 
        #selfはMyTestのインスタンスです
        #self.classはMyTestです
  end
end

my_test = MyTest.new
my_test.helpers {
  def foo()
    p "my_test.foo"
    super
  end
}

my_test.foo
# output :
# "my_test.foo"
# "MyBase::foo"

file11.rb

require 'sinatra'
get '/hello/:name' do
  "Hello #{params[:name]}!" 
    # ここのparamsは不思議なものです
    # なぜブロックの中にSinatra::Requestのparams属性がアクセス出来ます
end

file12.rb

# app を実装.

# get/post ブロックの中でRack::Requestの属性にアクセス出来ます

get do
  [200, {}, ["hello world // Get : params : " + params.to_s + "\n"]]
end

post do
  [200, {}, ["hello world // POST : body : " + body.read + "\n"]]
end

file13.rb

# library を実装

require 'rack'
class MyRackApp
  @@process_map = {}
  def self.register(method, proc)
    @@process_map[method] = proc
  end

  def call(env)
    request = Rack::Request.new(env)
    proc = @@process_map[request.request_method]
    if proc.nil?
      [500, {}, ["未実装"]]
    else
      request.instance_eval(&proc)
    end
  end
end

def get(&proc)
  MyRackApp.register('GET', proc)
end
def post(&proc)
  MyRackApp.register('POST', proc)
end

# app を実装

get do
  [200, {}, ["hello world // Get : params : " + params.to_s + "\n"]]
end

post do
  [200, {}, ["hello world // POST : body : " + body.read + "\n"]]
end

# library を実装
rack_app = MyRackApp.new
Rack::Handler::WEBrick.run rack_app, :Port=>3000

file2.rb

enumerator = {a:1, b:2}.map()
# => #<Enumerator: {:a=>1, :b=>2}:map>

enumerator.method(:with_index)
#=> #<Method: Enumerator#with_index>
    # with_indexはEnumeratorのメソッドです
enumerator.with_index() {|(key,value), index| 
  "#{index} : #{key} => #{value}"
}
#=> ["0 : a => 1", "1 : b => 2"]

file3.txt

文法:
method(arg1, arg2, ...)  do [`|' 式 ... `|'] 式 ... end
method(arg1, arg2, ...) `{' [`|' 式 ... `|'] 式 ... `}'
method(arg1, arg2, ..., `&' proc_object)

file4.rb

["A","B","C"].map{|a| a.downcase}
#=> ["a", "b", "c"]
["A","B","C"].map(&:downcase)
#=> ["a", "b", "c"]

# &:downcaseは式の形ですけど、実は評価出来ないものです。
&:downcase
#    SyntaxError: (irb):21: syntax error, unexpected &
#    &:downcase
#     ^
#      from /usr/local/bin/irb:11:in `<main>'

file5.rb

proc = Proc.new { |a| a.downcase }
["A","B","C"].map &proc
#=> ["a", "b", "c"]

&proc
#    SyntaxError: (irb):31: syntax error, unexpected &
#    &proc
#     ^
#       from /usr/local/bin/irb:11:in `<main>'
#    

file6.rb

file_contents = ''
f = File.open('.vimrc', 'r')
file_contents = f.read
f.close

file7.rb

file_contents = File.open('.vimrc', 'r') {|f| f.read }

file8.rb

def my_fopen(name, mode)
  f = File.open(name, mode)
  return f unless block_given?

  begin
    yield f
  ensure
    p "ensure : f.close"
    f.close
  end
end

# style 1:
file_contents = ''
f = my_fopen('.vimrc', 'r')
file_contents = f.read
f.close
p file_contents

# style 2:
file_contents = my_fopen('.vimrc', 'r') {|f| f.read }
p file_contents

file9.rb

# Sinatra helpers例
helpers do
  def find_template(views, name, engine, &block)
    ....
    super(folder, name, engine, &block)
  end
end