require "active_support"

{ a: 1 }.with_indifferent_access["a"] # => 1

require "active_support"
require "active_support/core_ext/hash/indifferent_access"

require "active_support"
require "active_support/core_ext/hash"

require "active_support"
require "active_support/core_ext"

require "active_support/all"

def authenticate(controller, &login_procedure)
  token, options = token_and_options(controller.request)
  unless token.blank?
    login_procedure.call(token, options)
  end
end

def set_conditional_cache_control!
  return if self["Cache-Control"].present?
  # ...
end

"foo".dup           # => "foo"
"".dup              # => ""
Rational(1).dup     # => (1/1)
Complex(0).dup      # => (0+0i)
1.method(:+).dup    # => TypeError (Method没有定义分配器)

"foo".duplicable?           # => true
"".duplicable?              # => true
Rational(1).duplicable?     # => true
Complex(1).duplicable?      # => true
1.method(:+).duplicable?    # => false

array     = ['string']
duplicate = array.dup

duplicate.push 'another-string'

# 对象已复制，因此元素仅添加到副本中
array     # => ['string']
duplicate # => ['string', 'another-string']

duplicate.first.gsub!('string', 'foo')

# 第一个元素没有复制，它将在两个数组中都被更改
array     # => ['foo']
duplicate # => ['foo', 'another-string']

array     = ['string']
duplicate = array.deep_dup

duplicate.first.gsub!('string', 'foo')

array     # => ['string']
duplicate # => ['foo']

number = 1
duplicate = number.deep_dup
number.object_id == duplicate.object_id   # => true

# 不使用try
unless @number.nil?
  @number.next
end

# 使用try
@number.try(:next)

def log_info(sql, name, ms)
  if @logger.try(:debug?)
    name = '%s (%.1fms)' % [name || 'SQL', ms]
    @logger.debug(format_log_entry(name, sql.squeeze(' ')))
  end
end

@person.try { |p| "#{p.first_name} #{p.last_name}" }

@number.try(:nest)  # => nil
@number.try!(:nest) # NoMethodError: undefined method `nest' for 1:Integer

class Proc
  def bind(object)
    block, time = self, Time.current
    object.class_eval do
      method_name = "__bind_#{time.to_i}_#{time.usec}"
      define_method(method_name, &block)
      method = instance_method(method_name)
      remove_method(method_name)
      method
    end.bind(object)
  end
end

some_klass.acts_like?(:string)

7.to_param # => "7"

"Tom & Jerry".to_param # => "Tom & Jerry"

[0, true, String].to_param # => "0/true/String"

class User
  def to_param
    "#{id}-#{name.parameterize}"
  end
end

user_path(@user) # => "/users/357-john-smith"

class User
  def to_param
    "#{id}-#{name.parameterize}"
  end
end

current_user.to_query('user') # => "user=357-john-smith"

account.to_query('company[name]')
# => "company%5Bname%5D=Johnson+%26+Johnson"

[3.4, -45.6].to_query('sample')
# => "sample%5B%5D=3.4&sample%5B%5D=-45.6"

{ c: 3, b: 2, a: 1 }.to_query # => "a=1&b=2&c=3"

{ id: 89, name: "John Smith" }.to_query('user')
# => "user%5Bid%5D=89&user%5Bname%5D=John+Smith"

class Account < ApplicationRecord
  has_many :customers, dependent: :destroy
  has_many :products,  dependent: :destroy
  has_many :invoices,  dependent: :destroy
  has_many :expenses,  dependent: :destroy
end

class Account < ApplicationRecord
  with_options dependent: :destroy do |assoc|
    assoc.has_many :customers
    assoc.has_many :products
    assoc.has_many :invoices
    assoc.has_many :expenses
  end
end

I18n.with_options locale: user.locale, scope: "newsletter" do |i18n|
  subject i18n.t :subject
  body    i18n.t :body, user_name: user.name
end

class C
  def initialize(x, y)
    @x, @y = x, y
  end
end

C.new(0, 1).instance_values # => {"x" => 0, "y" => 1}

class C
  def initialize(x, y)
    @x, @y = x, y
  end
end

C.new(0, 1).instance_variable_names # => ["@x", "@y"]

silence_warnings { Object.const_set "RAILS_DEFAULT_LOGGER", logger }

# 如果用户被锁定，增量将丢失，没关系。
suppress(ActiveRecord::StaleObjectError) do
  current_user.increment! :visits
end

1.in?([1, 2])        # => true
"lo".in?("hello")   # => true
25.in?(30..50)      # => false
1.in?(1)            # => ArgumentError

class User < ApplicationRecord
  # 您可以将email列称为"login"。
  # 这对于身份验证代码可能是有意义的。
  alias_attribute :login, :email
end

# library
class ThirdPartyLibrary::Crawler
  attr_internal :log_level
end

# client code
class MyCrawler < ThirdPartyLibrary::Crawler
  attr_accessor :log_level
end

module ActionView
  class Base
    attr_internal :captures
    attr_internal :request, :layout
    attr_internal :controller, :template
  end
end

module ActiveStorage
  mattr_accessor :logger
end

module X
  module Y
    module Z
    end
  end
end
M = X::Y::Z

X::Y::Z.module_parent # => X::Y
M.module_parent       # => X::Y

module X
  module Y
    module Z
    end
  end
end
M = X::Y::Z

X::Y::Z.module_parent_name # => "X::Y"
M.module_parent_name       # => "X::Y"

module X
  module Y
    module Z
    end
  end
end
M = X::Y::Z

X::Y::Z.module_parents # => [X::Y, X, Object]
M.module_parents       # => [X::Y, X, Object]

module M
end
M.name # => "M"

N = Module.new
N.name # => "N"

Module.new.name # => nil

module M
end
M.anonymous? # => false

Module.new.anonymous? # => true

module M
end

m = Object.send(:remove_const, :M)

m.anonymous? # => false

class User < ApplicationRecord
  has_one :profile
end

class User < ApplicationRecord
  has_one :profile

  def name
    profile.name
  end
end

class User < ApplicationRecord
  has_one :profile

  delegate :name, to: :profile
end

delegate :name, :age, :address, :twitter, to: :profile

# 委托给Rails常量
delegate :logger, to: :Rails

# 委托给接收器的类
delegate :table_name, to: :class

delegate :name, to: :profile, allow_nil: true

delegate :street, to: :address, prefix: true

delegate :size, to: :attachment, prefix: :avatar

delegate :date_of_birth, to: :profile, private: true

class User < ApplicationRecord
  has_one :profile

  delegate_missing_to :profile
end

class A
  class_attribute :x
end

class B < A; end

class C < B; end

A.x = :a
B.x # => :a
C.x # => :a

B.x = :b
A.x # => :a
C.x # => :b

C.x = :c
A.x # => :a
B.x # => :b

class_attribute :default_params
self.default_params = {
  mime_version: "1.0",
  charset: "UTF-8",
  content_type: "text/plain",
  parts_order: [ "text/plain", "text/enriched", "text/html" ]
}.freeze

A.x = 1

a1 = A.new
a2 = A.new
a2.x = 2

a1.x # => 1，来自 A
a2.x # => 2，在 a2 中被覆盖

module ActiveRecord
  class Base
    class_attribute :table_name_prefix, instance_writer: false, default: "my"
  end
end

class A
  class_attribute :x, instance_reader: false
end

A.new.x = 1
A.new.x # NoMethodError

class MysqlAdapter < AbstractAdapter
  # 生成访问 @@emulate_booleans 的类方法。
  cattr_accessor :emulate_booleans
end

class MysqlAdapter < AbstractAdapter
  # 生成访问 @@emulate_booleans 的类方法，并将默认值设置为 true。
  cattr_accessor :emulate_booleans, default: true
end

module ActionView
  class Base
    cattr_accessor :field_error_proc, default: Proc.new { ... }
  end
end

module A
  class B
    # 不会生成first_name实例读取器。
    cattr_accessor :first_name, instance_reader: false
    # 不会生成last_name=实例写入器。
    cattr_accessor :last_name, instance_writer: false
    # 不会生成surname实例读取器或surname=写入器。
    cattr_accessor :surname, instance_accessor: false
  end
end

class C; end
C.subclasses # => []

class B < C; end
C.subclasses # => [B]

class A < B; end
C.subclasses # => [B]

class D < C; end
C.subclasses # => [B, D]

class C; end
C.descendants # => []

class B < C; end
C.descendants # => [B]

class A < B; end
C.descendants # => [B, A]

class D < C; end
C.descendants # => [B, A, D]

"".html_safe? # => false

s = "".html_safe
s.html_safe? # => true

s = "<script>...</script>".html_safe
s.html_safe? # => true
s            # => "<script>...</script>"

"".html_safe + "<" # => "&lt;"

"".html_safe + "<".html_safe # => "<"

<%= @review.title %> <%# 如果需要，会被转义 %>

<%= raw @cms.current_template %> <%# 将 @cms.current_template 原样插入 %>

<%== @cms.current_template %> <%# 将 @cms.current_template 原样插入 %>

def raw(stringish)
  stringish.to_s.html_safe
end

"Hello World".remove(/Hello /) # => "World"

" \n  foo\n\r \t bar \n".squish # => "foo bar"

"Oh dear! Oh dear! I shall be late!".truncate(20)
# => "Oh dear! Oh dear!..."

"Oh dear! Oh dear! I shall be late!".truncate(20, omission: '…')
# => "Oh dear! Oh …"

"Oh dear! Oh dear! I shall be late!".truncate(18)
# => "Oh dear! Oh dea..."
"Oh dear! Oh dear! I shall be late!".truncate(18, separator: ' ')
# => "Oh dear! Oh..."

"Oh dear! Oh dear! I shall be late!".truncate(18, separator: /\s/)
# => "Oh dear! Oh..."

"👍👍👍👍".truncate_bytes(15)
# => "👍👍👍…"

"👍👍👍👍".truncate_bytes(15, omission: "🖖")
# => "👍👍🖖"

"Oh dear! Oh dear! I shall be late!".truncate_words(4)
# => "Oh dear! Oh dear!..."

"Oh dear! Oh dear! I shall be late!".truncate_words(4, omission: '…')
# => "Oh dear! Oh dear!…"

"Oh dear! Oh dear! I shall be late!".truncate_words(3, separator: '!')
# => "Oh dear! Oh dear! I shall be late..."

"Oh dear! Oh dear! I shall be late!".truncate_words(4, separator: /\s/)
# => "Oh dear! Oh dear!..."

"production".inquiry.production? # => true
"active".inquiry.inactive?       # => false

"foo".starts_with?("f") # => true
"foo".ends_with?("o")   # => true

if options[:usage]
  puts <<-USAGE.strip_heredoc
    This command does such and such.

    Supported options are:
      -h         This message
      ...
  USAGE
end

<<EOS.indent(2)
def some_method
  some_code
end
EOS
# =>
  def some_method
    some_code
  end

"  foo".indent(2)        # => "    foo"
"foo\n\t\tbar".indent(2) # => "\t\tfoo\n\t\t\t\tbar"
"foo".indent(2, "\t")    # => "\t\tfoo"

"foo\n\nbar".indent(2)            # => "  foo\n\n  bar"
"foo\n\nbar".indent(2, nil, true) # => "  foo\n  \n  bar"

"hello".at(0)  # => "h"
"hello".at(4)  # => "o"
"hello".at(-1) # => "o"
"hello".at(10) # => nil

"hello".from(0)  # => "hello"
"hello".from(2)  # => "llo"
"hello".from(-2) # => "lo"
"hello".from(10) # => nil

"hello".to(0)  # => "h"
"hello".to(2)  # => "hel"
"hello".to(-2) # => "hell"
"hello".to(10) # => "hello"

"table".pluralize     # => "tables"
"ruby".pluralize      # => "rubies"
"equipment".pluralize # => "equipment"

"dude".pluralize(0) # => "dudes"
"dude".pluralize(1) # => "dude"
"dude".pluralize(2) # => "dudes"

# active_record/model_schema.rb
def undecorated_table_name(model_name)
  table_name = model_name.to_s.demodulize.underscore
  pluralize_table_names ? table_name.pluralize : table_name
end

"tables".singularize    # => "table"
"rubies".singularize    # => "ruby"
"equipment".singularize # => "equipment"

# active_record/reflection.rb
def derive_class_name
  class_name = name.to_s.camelize
  class_name = class_name.singularize if collection?
  class_name
end

"product".camelize    # => "Product"
"admin_user".camelize # => "AdminUser"

"backoffice/session".camelize # => "Backoffice::Session"

# action_controller/metal/session_management.rb
def session_store=(store)
  @@session_store = store.is_a?(Symbol) ?
    ActionDispatch::Session.const_get(store.to_s.camelize) :
    store
end

"visual_effect".camelize(:lower) # => "visualEffect"

ActiveSupport::Inflector.inflections do |inflect|
  inflect.acronym 'SSL'
end

"SSLError".underscore.camelize # => "SSLError"

"Product".underscore   # => "product"
"AdminUser".underscore # => "admin_user"

"Backoffice::Session".underscore # => "backoffice/session"

"visualEffect".underscore # => "visual_effect"

# actionpack/lib/abstract_controller/base.rb
def controller_path
  @controller_path ||= name.delete_suffix("Controller").underscore
end

"alice in wonderland".titleize # => "Alice In Wonderland"
"fermat's enigma".titleize     # => "Fermat's Enigma"

"name".dasherize         # => "name"
"contact_data".dasherize # => "contact-data"

# active_model/serializers/xml.rb
def reformat_name(name)
  name = name.camelize if camelize?
  dasherize? ? name.dasherize : name
end

"Product".demodulize                        # => "Product"
"Backoffice::UsersController".demodulize    # => "UsersController"
"Admin::Hotel::ReservationUtils".demodulize # => "ReservationUtils"
"::Inflections".demodulize                  # => "Inflections"
"".demodulize                               # => ""

# active_record/reflection.rb
def counter_cache_column
  if options[:counter_cache] == true
    "#{active_record.name.demodulize.underscore.pluralize}_count"
  elsif options[:counter_cache]
    options[:counter_cache]
  end
end

"Product".deconstantize                        # => ""
"Backoffice::UsersController".deconstantize    # => "Backoffice"
"Admin::Hotel::ReservationUtils".deconstantize # => "Admin::Hotel"

"John Smith".parameterize # => "john-smith"
"Kurt Gödel".parameterize # => "kurt-godel"

"John Smith".parameterize(preserve_case: true) # => "John-Smith"
"Kurt Gödel".parameterize(preserve_case: true) # => "Kurt-Godel"

2.multiple_of?(1) # => true
1.multiple_of?(2) # => false

1.ordinal    # => "st"
2.ordinal    # => "nd"
53.ordinal   # => "rd"
2009.ordinal # => "th"
-21.ordinal  # => "st"
-134.ordinal # => "th"

1.ordinalize    # => "1st"
2.ordinalize    # => "2nd"
53.ordinalize   # => "53rd"
2009.ordinalize # => "2009th"
-21.ordinalize  # => "-21st"
-134.ordinalize # => "-134th"

# 等同于 Time.current.advance(months: 1)
1.month.from_now

# 等同于 Time.current.advance(years: 2)
2.years.from_now

# 等同于 Time.current.advance(months: 4, years: 5)
(4.months + 5.years).from_now

BigDecimal(5.00, 6).to_s       # => "5.0"

BigDecimal(5.00, 6).to_s("e")  # => "0.5E1"

[1, 2, 3].sum # => 6
(1..100).sum  # => 5050

[[1, 2], [2, 3], [3, 4]].sum    # => [1, 2, 2, 3, 3, 4]
%w(foo bar baz).sum             # => "foobarbaz"
{ a: 1, b: 2, c: 3 }.sum          # => [:a, 1, :b, 2, :c, 3]

[].sum    # => 0
[].sum(1) # => 1

(1..5).sum { |n| n * 2 } # => 30
[2, 4, 6, 8, 10].sum    # => 30

[].sum(1) { |n| n**3 } # => 1

invoices.index_by(&:number)
# => {'2009-032' => <Invoice ...>, '2009-008' => <Invoice ...>, ...}

post = Post.new(title: "hey there", body: "what's up?")

%i( title body ).index_with { |attr_name| post.public_send(attr_name) }
# => { title: "hey there", body: "what's up?" }

WEEKDAYS.index_with(Interval.all_day)
# => { monday: [ 0, 1440 ], … }

<% if pages.many? %>
  <%= pagination_links %>
<% end %>

@see_more = videos.many? { |video| video.category == params[:category] }

to_visit << node if visited.exclude?(node)

[ 1, 2, 3 ].including(4, 5)                    # => [ 1, 2, 3, 4, 5 ]
["David", "Rafael"].including %w[ Aaron Todd ] # => ["David", "Rafael", "Aaron", "Todd"]

["David", "Rafael", "Aaron", "Todd"].excluding("Aaron", "Todd") # => ["David", "Rafael"]

[{ name: "David" }, { name: "Rafael" }, { name: "Aaron" }].pluck(:name) # => ["David", "Rafael", "Aaron"]
[{ id: 1, name: "David" }, { id: 2, name: "Rafael" }].pluck(:id, :name) # => [[1, "David"], [2, "Rafael"]]

[{ name: "David" }, { name: "Rafael" }, { name: "Aaron" }].pick(:name) # => "David"
[{ id: 1, name: "David" }, { id: 2, name: "Rafael" }].pick(:id, :name) # => [1, "David"]

%w(a b c d).to(2) # => ["a", "b", "c"]
[].to(7)          # => []

%w(a b c d).from(2)  # => ["c", "d"]
%w(a b c d).from(10) # => []
[].from(0)           # => []

[ 1, 2, 3 ].including(4, 5)          # => [ 1, 2, 3, 4, 5 ]
[ [ 0, 1 ] ].including([ [ 1, 0 ] ]) # => [ [ 0, 1 ], [ 1, 0 ] ]

["David", "Rafael", "Aaron", "Todd"].excluding("Aaron", "Todd") # => ["David", "Rafael"]
[ [ 0, 1 ], [ 1, 0 ] ].excluding([ [ 1, 0 ] ])                  # => [ [ 0, 1 ] ]

%w(a b c d).third # => "c"
%w(a b c d).fifth # => nil

numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
odd_numbers = numbers.extract! { |number| number.odd? } # => [1, 3, 5, 7, 9]
numbers # => [0, 2, 4, 6, 8]

User.exists?(email: params[:email])

def caches_action(*actions)
  return unless cache_configured?
  options = actions.extract_options!
  # ...
end

%w().to_sentence                # => ""
%w(Earth).to_sentence           # => "Earth"
%w(Earth Wind).to_sentence      # => "Earth and Wind"
%w(Earth Wind Fire).to_sentence # => "Earth, Wind, and Fire"

[].to_fs(:db)            # => "null"
[user].to_fs(:db)        # => "8456"
invoice.lines.to_fs(:db) # => "23,567,556,12"

Contributor.limit(2).order(:rank).to_xml
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <contributors type="array">
#   <contributor>
#     <id type="integer">4356</id>
#     <name>Jeremy Kemper</name>
#     <rank type="integer">1</rank>
#     <url-id>jeremy-kemper</url-id>
#   </contributor>
#   <contributor>
#     <id type="integer">4404</id>
#     <name>David Heinemeier Hansson</name>
#     <rank type="integer">2</rank>
#     <url-id>david-heinemeier-hansson</url-id>
#   </contributor>
# </contributors>

如果接收者是一个哈希数组，则默认的根元素也是“objects”：

```ruby
[{ a: 1, b: 2 }, { c: 3 }].to_xml
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <objects type="array">
#   <object>
#     <b type="integer">2</b>
#     <a type="integer">1</a>
#   </object>
#   <object>
#     <c type="integer">3</c>
#   </object>
# </objects>

Contributor.limit(2).order(:rank).to_xml(skip_types: true)
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <contributors>
#   <contributor>
#     <id>4356</id>
#     <name>Jeremy Kemper</name>
#     <rank>1</rank>
#     <url-id>jeremy-kemper</url-id>
#   </contributor>
#   <contributor>
#     <id>4404</id>
#     <name>David Heinemeier Hansson</name>
#     <rank>2</rank>
#     <url-id>david-heinemeier-hansson</url-id>
#   </contributor>
# </contributors>

Array.wrap(nil)       # => []
Array.wrap([1, 2, 3]) # => [1, 2, 3]
Array.wrap(0)         # => [0]

Array.wrap(foo: :bar) # => [{:foo=>:bar}]
Array(foo: :bar)      # => [[:foo, :bar]]

[*object]

array = [1, [2, 3]]
dup = array.deep_dup
dup[1][2] = 4
array[1][2] == nil   # => true

[1, 2, 3].in_groups_of(2) # => [[1, 2], [3, nil]]

<% sample.in_groups_of(3) do |a, b, c| %>
  <tr>
    <td><%= a %></td>
    <td><%= b %></td>
    <td><%= c %></td>
  </tr>
<% end %>

[1, 2, 3].in_groups_of(2, 0) # => [[1, 2], [3, 0]]

[1, 2, 3].in_groups_of(2, false) # => [[1, 2], [3]]

%w(1 2 3 4 5 6 7).in_groups(3)
# => [["1", "2", "3"], ["4", "5", nil], ["6", "7", nil]]

%w(1 2 3 4 5 6 7).in_groups(3) { |group| p group }
["1", "2", "3"]
["4", "5", nil]
["6", "7", nil]

%w(1 2 3 4 5 6 7).in_groups(3, "0")
# => [["1", "2", "3"], ["4", "5", "0"], ["6", "7", "0"]]

%w(1 2 3 4 5 6 7).in_groups(3, false)
# => [["1", "2", "3"], ["4", "5"], ["6", "7"]]

(-5..5).to_a.split { |i| i.multiple_of?(4) }
# => [[-5], [-3, -2, -1], [1, 2, 3], [5]]

[0, 1, -5, 1, 1, "foo", "bar"].split(1)
# => [[0], [-5], [], ["foo", "bar"]]

{ foo: 1, bar: 2 }.to_xml
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <hash>
#   <foo type="integer">1</foo>
#   <bar type="integer">2</bar>
# </hash>

{ a: 1, b: 1 }.merge(a: 0, c: 2)
# => {:a=>0, :b=>1, :c=>2}

options = { length: 30, omission: "..." }.merge(options)

options = options.reverse_merge(length: 30, omission: "...")

options.reverse_merge!(length: 30, omission: "...")

{ a: { b: 1 } }.deep_merge(a: { c: 2 })
# => {:a=>{:b=>1, :c=>2}}

hash = { a: 1, b: { c: 2, d: [3, 4] } }

dup = hash.deep_dup
dup[:b][:e] = 5
dup[:b][:d] << 5

hash[:b][:e] == nil      # => true
hash[:b][:d] == [3, 4]   # => true

{ a: 1, b: 2 }.except(:a) # => {:b=>2}

{ a: 1 }.with_indifferent_access.except(:a)  # => {}
{ a: 1 }.with_indifferent_access.except("a") # => {}

{ nil => nil, 1 => 1, a: :a }.stringify_keys
# => {"" => nil, "1" => 1, "a" => :a}

{ "a" => 1, a: 2 }.stringify_keys
# 结果将是
# => {"a"=>2}

def to_check_box_tag(options = {}, checked_value = "1", unchecked_value = "0")
  options = options.stringify_keys
  options["type"] = "checkbox"
  # ...
end

{ nil => nil, 1 => 1, nested: { a: 3, 5 => 5 } }.deep_stringify_keys
# => {""=>nil, "1"=>1, "nested"=>{"a"=>3, "5"=>5}}

{ nil => nil, 1 => 1, "a" => "a" }.symbolize_keys
# => {nil=>nil, 1=>1, :a=>"a"}

{ "a" => 1, a: 2 }.symbolize_keys
# => {:a=>2}

def rich_text_area_tag(name, value = nil, options = {})
  options = options.symbolize_keys

  options[:input] ||= "trix_input_#{ActionText::TagHelper.id += 1}"
  # ...
end

{ nil => nil, 1 => 1, "nested" => { "a" => 3, 5 => 5 } }.deep_symbolize_keys
# => {nil=>nil, 1=>1, nested:{a:3, 5=>5}}

{ a: 1 }.assert_valid_keys(:a)  # 通过
{ a: 1 }.assert_valid_keys("a") # ArgumentError

hash = { person: { name: 'Rob', age: '28' } }

hash.deep_transform_values { |value| value.to_s.upcase }
# => {person: {name: "ROB", age: "28"}}

hash = { a: 1, b: 2 }
rest = hash.slice!(:a) # => {:b=>2}
hash                   # => {:a=>1}

hash = { a: 1, b: 2 }
rest = hash.extract!(:a) # => {:a=>1}
hash                     # => {:b=>2}

注意：定义在 `active_support/core_ext/hash/slice.rb` 中。


### 无差别访问

方法 [`with_indifferent_access`][Hash#with_indifferent_access] 返回一个 [`ActiveSupport::HashWithIndifferentAccess`][ActiveSupport::HashWithIndifferentAccess] 对象：

```ruby
{ a: 1 }.with_indifferent_access["a"] # => 1

%r{.}.multiline?  # => false
%r{.}m.multiline? # => true

Regexp.new('.').multiline?                    # => false
Regexp.new('.', Regexp::MULTILINE).multiline? # => true

def verify_regexp_requirements(requirements)
  # ...
  if requirement.multiline?
    raise ArgumentError, "Regexp multiline option is not allowed in routing requirements: #{requirement.inspect}"
  end
  # ...
end

(Date.today..Date.tomorrow).to_fs
# => "2009-10-25..2009-10-26"

(Date.today..Date.tomorrow).to_fs(:db)
# => "BETWEEN '2009-10-25' AND '2009-10-26'"

(2..3).include?(Math::E) # => true

(1..10) === (3..7)  # => true
(1..10) === (0..7)  # => false
(1..10) === (3..11) # => false
(1...9) === (3..9)  # => false

(1..10).include?(3..7)  # => true
(1..10).include?(0..7)  # => false
(1..10).include?(3..11) # => false
(1...9).include?(3..9)  # => false

(1..10).overlap?(7..11)  # => true
(1..10).overlap?(0..7)   # => true
(1..10).overlap?(11..27) # => false

d = Date.new(2010, 5, 8)     # => Sat, 08 May 2010
d.beginning_of_week          # => Mon, 03 May 2010
d.beginning_of_week(:sunday) # => Sun, 02 May 2010
d.end_of_week                # => Sun, 09 May 2010
d.end_of_week(:sunday)       # => Sat, 08 May 2010

d = Date.new(2010, 5, 8)     # => Sat, 08 May 2010
d.monday                     # => Mon, 03 May 2010
d.sunday                     # => Sun, 09 May 2010

d = Date.new(2012, 9, 10)    # => Mon, 10 Sep 2012
d.monday                     # => Mon, 10 Sep 2012

d = Date.new(2012, 9, 16)    # => Sun, 16 Sep 2012
d.sunday                     # => Sun, 16 Sep 2012

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.next_week              # => Mon, 10 May 2010
d.next_week(:saturday)   # => Sat, 15 May 2010

d.prev_week              # => Mon, 26 Apr 2010
d.prev_week(:saturday)   # => Sat, 01 May 2010
d.prev_week(:friday)     # => Fri, 30 Apr 2010

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.beginning_of_month     # => Sat, 01 May 2010
d.end_of_month           # => Mon, 31 May 2010

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.quarter                # => 2

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.beginning_of_quarter   # => Thu, 01 Apr 2010
d.end_of_quarter         # => Wed, 30 Jun 2010

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.beginning_of_year      # => Fri, 01 Jan 2010
d.end_of_year            # => Fri, 31 Dec 2010

date = Date.new(2010, 6, 7)
date.years_ago(10) # => Wed, 07 Jun 2000

date = Date.new(2010, 6, 7)
date.years_since(10) # => Sun, 07 Jun 2020

Date.new(2012, 2, 29).years_ago(3)     # => Sat, 28 Feb 2009
Date.new(2012, 2, 29).years_since(3)   # => Sat, 28 Feb 2015

Date.new(2010, 4, 30).months_ago(2)   # => Sun, 28 Feb 2010
Date.new(2010, 4, 30).months_since(2) # => Wed, 30 Jun 2010

Date.new(2010, 4, 30).months_ago(2)    # => Sun, 28 Feb 2010
Date.new(2009, 12, 31).months_since(2) # => Sun, 28 Feb 2010

Date.new(2010, 5, 24).weeks_ago(1)    # => Mon, 17 May 2010
Date.new(2010, 5, 24).weeks_ago(2)    # => Mon, 10 May 2010

date = Date.new(2010, 6, 6)
date.advance(years: 1, weeks: 2)  # => Mon, 20 Jun 2011
date.advance(months: 2, days: -2) # => Wed, 04 Aug 2010

Date.new(2010, 12, 23).change(year: 2011, month: 11)
# => Wed, 23 Nov 2011

Date.new(2010, 1, 31).change(month: 2)
# => ArgumentError: invalid date

d = Date.current
# => Mon, 09 Aug 2010
d + 1.year
# => Tue, 09 Aug 2011
d - 3.hours
# => Sun, 08 Aug 2010 21:00:00 UTC +00:00

Date.new(1582, 10, 4) + 1.day
# => Fri, 15 Oct 1582

date = Date.new(2010, 6, 7)
date.beginning_of_day # => Mon Jun 07 00:00:00 +0200 2010

date = Date.new(2010, 6, 7)
date.end_of_day # => Mon Jun 07 23:59:59 +0200 2010

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.beginning_of_hour # => Mon Jun 07 19:00:00 +0200 2010

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.end_of_hour # => Mon Jun 07 19:59:59 +0200 2010

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.beginning_of_minute # => Mon Jun 07 19:55:00 +0200 2010

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.end_of_minute # => Mon Jun 07 19:55:59 +0200 2010

date = Date.current # => Fri, 11 Jun 2010
date.ago(1)         # => Thu, 10 Jun 2010 23:59:59 EDT -04:00

date = Date.current # => Fri, 11 Jun 2010
date.since(1)       # => Fri, 11 Jun 2010 00:00:01 EDT -04:00

now = DateTime.current     # => Mon, 07 Jun 2010 20:26:36 +0000
now.seconds_since_midnight # => 73596

now = DateTime.current # => Mon, 07 Jun 2010 19:27:52 -0400
now.utc                # => Mon, 07 Jun 2010 23:27:52 +0000

now = DateTime.now # => Mon, 07 Jun 2010 19:30:47 -0400
now.utc?           # => false
now.utc.utc?       # => true

d = DateTime.current
# => Thu, 05 Aug 2010 11:33:31 +0000
d.advance(years: 1, months: 1, days: 1, hours: 1, minutes: 1, seconds: 1)
# => Tue, 06 Sep 2011 12:34:32 +0000

d = DateTime.new(2010, 2, 28, 23, 59, 59)
# => Sun, 28 Feb 2010 23:59:59 +0000
d.advance(months: 1, seconds: 1)
# => Mon, 29 Mar 2010 00:00:00 +0000

d.advance(seconds: 1).advance(months: 1)
# => Thu, 01 Apr 2010 00:00:00 +0000

now = DateTime.current
# => Tue, 08 Jun 2010 01:56:22 +0000
now.change(year: 2011, offset: Rational(-6, 24))
# => Wed, 08 Jun 2011 01:56:22 -0600

now.change(hour: 0)
# => Tue, 08 Jun 2010 00:00:00 +0000

now.change(min: 0)
# => Tue, 08 Jun 2010 01:00:00 +0000

DateTime.current.change(month: 2, day: 30)
# => ArgumentError: invalid date

now = DateTime.current
# => Mon, 09 Aug 2010 23:15:17 +0000
now + 1.year
# => Tue, 09 Aug 2011 23:15:17 +0000
now - 1.week
# => Mon, 02 Aug 2010 23:15:17 +0000

DateTime.new(1582, 10, 4, 23) + 1.hour
# => Fri, 15 Oct 1582 00:00:00 +0000

Time.zone_default
# => #<ActiveSupport::TimeZone:0x7f73654d4f38 @utc_offset=nil, @name="Madrid", ...>

# 在巴塞罗那，2010/03/28 02:00 +0100 由于夏令时变为 2010/03/28 03:00 +0200。
t = Time.local(2010, 3, 28, 1, 59, 59)
# => Sun Mar 28 01:59:59 +0100 2010
t.advance(seconds: 1)
# => Sun Mar 28 03:00:00 +0200 2010

now = Time.current
# => Mon, 09 Aug 2010 23:20:05 UTC +00:00
now.all_day
# => Mon, 09 Aug 2010 00:00:00 UTC +00:00..Mon, 09 Aug 2010 23:59:59 UTC +00:00

now = Time.current
# => Mon, 09 Aug 2010 23:20:05 UTC +00:00
now.all_week
# => Mon, 09 Aug 2010 00:00:00 UTC +00:00..Sun, 15 Aug 2010 23:59:59 UTC +00:00
now.all_week(:sunday)
# => Sun, 16 Sep 2012 00:00:00 UTC +00:00..Sat, 22 Sep 2012 23:59:59 UTC +00:00
now.all_month
# => Sat, 01 Aug 2010 00:00:00 UTC +00:00..Tue, 31 Aug 2010 23:59:59 UTC +00:00
now.all_quarter
# => Thu, 01 Jul 2010 00:00:00 UTC +00:00..Thu, 30 Sep 2010 23:59:59 UTC +00:00
now.all_year
# => Fri, 01 Jan 2010 00:00:00 UTC +00:00..Fri, 31 Dec 2010 23:59:59 UTC +00:00