ifuser.active?send_mail_to(user)end

send_mail_to(user)ifuser.active?

user.destroyif!user.active?

user.destroyunlessuser.active?

# こんなunlessは理解するのに時間がかかるのでNGuser.destroyunless(user.active?||user.admin?)&&!user.spam?

ifuser.admin?"I appreciate for that."else"Thanks."end

user.admin??"I appreciate for that.":"Thanks"

# 三項演算子のネストは読みづらいuser.admin??user.active??"I appreciate for that.":"Are you OK?":"Thanks."

iffoo==true# ...endifbar==false# ...end

iffoo# ...endunlessbar# ...end# またはif!bar# ...end

ifbaz==nil# ...end

unlessbaz# ...end# またはif!baz# ...end

ifbaz.nil?# bazがnilのときだけ実行される# （bazがfalseだったら実行されない）end

user=find_userifusersend_mail_to(user)end

ifuser=find_usersend_mail_to(user)end

ifparent.childrenifparent.children.singleton?singleton=parent.children.firstsend_mail_to(singleton)endend

ifparent.children&&parent.children.singleton?singleton=parent.children.firstsend_mail_to(singleton)end

# Ruby 2.3以降（childrenがnilでもエラーにならず、nilが返る）ifparent.children&.singleton?singleton=parent.children.firstsend_mail_to(singleton)end

defbuild_message(user)message='hello'message+='!!'ifuser.admin?returnmessageend

defbuild_message(user)message='hello'message+='!!'ifuser.admin?messageend

defbuild_useruser=User.newuser.email="hoge@hoge.com"user.name="Taro Yamada"userend

defbuild_userUser.new.tapdo|user|user.email="hoge@hoge.com"user.name="Taro Yamada"endend

"Hello, "+user.name+"!"

"Hello,#{user.name}!"

text="Hello, world!\nGood-bye, world!"

text=<<-TEXTHello, world!Good-bye, world!TEXT

CONTACT_PHONE_NUMBER="03-1234-5678"CONTACT_PHONE_NUMBER<<"@#$%^"putsCONTACT_PHONE_NUMBER# => 03-1234-5678@#$%^

CONTACT_PHONE_NUMBER="03-1234-5678".freezeCONTACT_PHONE_NUMBER<<"@#$%^"# => RuntimeError: can't modify frozen String

ADMIN_NAMES=["Tom","Alice"]ADMIN_NAMES<<"Taro"ADMIN_NAMES[0].downcase!pADMIN_NAMES# => ["tom", "Alice", "Taro"]

ADMIN_NAMES=["Tom","Alice"].freeze.each(&:freeze)ADMIN_NAMES<<"Taro"# => RuntimeError: can't modify frozen ArrayADMIN_NAMES[0].downcase!# => RuntimeError: can't modify frozen String

# エラーにはならないが、あまり意味が無いITEM_LIMIT=500.freeze

countries=[:japan,:italy,:uk]capitals={japan:'Tokyo',italy:'Rome',uk:'London'}

countries=[:japan,:italy,:uk,]capitals={japan:'Tokyo',italy:'Rome',uk:'London',}

countries=[:japan,:italy,:uk,:india,# <= 1つ前の行を修正せずに追加]capitals={japan:'Tokyo',italy:'Rome',uk:'London',india:'New Delhi',# <= 1つ前の行を修正せずに追加}

actions=['index','new','create']

actions=%w(index new create)# => ['index', 'new', 'create']

actions=%i(index new create)# => [:index, :new, :create]

names=users.map{|user|user.name}

names=users.map(&:name)

# usersはnilが渡される場合もあるので分岐するifusersusers.each{|user|send_direct_mail(user)}end

# Array()を使うと、nilの場合は空の配列（[])が、それ以外は元の配列が返されるので分岐が不要Array(users).each{|user|send_direct_mail(user)}

ITEM_LIMIT=1000000000

ITEM_LIMIT=1_000_000_000

classPersondefinitialize@name="No name"enddefname@nameendend

classPersonattr_reader:namedefinitialize@name="No name"end# いらない# def name#   @name# endend

ans_array=14.divmod(3)puts"商は#{ans_array[0]}"# => 商は4puts"あまりは#{ans_array[1]}"# => あまりは2

quotient,remainder=14.divmod(3)puts"商は#{quotient}"# => 商は4puts"あまりは#{remainder}"# => あまりは2

# keyとvalueを配列として受け取る{name:'Tom',email:'hoge@hoge.com'}.eachdo|key_and_value|puts"key:#{key_and_value[0]}"puts"value:#{key_and_value[1]}"end

# keyとvalueを別々の変数で受け取る{name:'Tom',email:'hoge@hoge.com'}.eachdo|key,value|puts"key:#{key}"puts"value:#{value}"end

numbers=[1,2,3]numbers_with_zero_and_100=[0]+numbers+[100]# => [0, 1, 2, 3, 100]

numbers=[1,2,3]numbers_with_zero_and_100=[0,*numbers,100]# => [0, 1, 2, 3, 100]

[0,numbers,100]# => [0, [1, 2, 3], 100]

deftwitter_client@twitter_client=Twitter::REST::Client.newif@twitter_client.nil?@twitter_clientend

deftwitter_client@twitter_client||=Twitter::REST::Client.newend

deftwitter_clientreturn@twitter_clientif@twitter_client@twitter_client=Twitter::REST::Client.new# 初期化に必要な処理# ...@twitter_clientend

deftwitter_client@twitter_client||=beginclient=Twitter::REST::Client.new# 初期化に必要な処理# ...clientendend

# キーに文字列を使うcurrencies={'japan'=>'yen','america'=>'dollar','italy'=>'euro'}currencies['japan']# => 'yen'

# キーにシンボルを使うcurrencies={japan:'yen',america:'dollar',italy:'euro'}currencies[:japan]# => 'yen'

defprocess_user(user)beginsend_to_mail(user)rescue# 例外処理endend

defprocess_user(user)send_to_mail(user)rescue# 例外処理end

defprocess_user(user)send_to_mail(user)rescueException=>ex# NoMemoryError等の致命的な例外まで捕捉してしまうので良くないend

defprocess_user(user)send_to_mail(user)rescue=>ex# すべての実行時エラー(＝ StandardErrorとそのサブクラス)が捕捉されるend

defprocess_user(user)send_to_mail(user)rescueArgumentError=>exifex.message=~/blah blah blah/# ArgumentErrorかつ、メッセージも条件に合致すれば# 別の処理を実行してそのまま続行するsend_to_admin(user,ex)else# メッセージが条件に合致しなかった場合は対処不能なエラーとして# 元のエラーを再度raiseするraiseendend

classUserprivatedefsecret_name# 外部から呼ばれたくないインスタンスメソッド"secret!"enddefself.secret_data# 外部から呼ばれたくないクラスメソッド！？"secret!!"endend

user=User.new# 呼び出せないuser.secret_name# => NoMethodError: private method `secret_name' called for #<User:0x007fa90c1e7cd0># 呼び出せるUser.secret_data# => "secret!!"

classUserprivatedefsecret_name# 外部から呼ばれたくないインスタンスメソッド"secret!"enddefself.secret_data# 外部から呼ばれたくないクラスメソッド"secret!!"end# secret_dataをprivateなクラスメソッドにするprivate_class_method:secret_dataend

User.secret_data# => NoMethodError: private method `secret_data' called for User:Class

classItemprivatedefsecret_price1000endend

classBook<Itemdefpublic_pricesecret_priceendend

book=Book.newbook.public_price# => 1000

numbers=[1,2,3,4,5]name='Taro Yamada'numbers[numbers.size-1]# => 5name[name.size-1]# => 'a'numbers[1..numbers.size-2]# => [2, 3, 4]name[1..name.size-2]# => "aro Yamad"

numbers=[1,2,3,4,5]name='Taro Yamada'numbers[-1]# => 5name[-1]# => 'a'numbers[1..-2]# => [2, 3, 4]name[1..-2]# => "aro Yamad"

deffind_admin(users)users.eachdo|user|returnuserifuser.admin?endnilend

deffind_admin(users)users.find(&:admin?)end

deffind_admins(users)admins=[]users.eachdo|user|admins<<userifuser.admin?endadminsend

deffind_admins(users)users.select(&:admin?)end

defcount_admin(users)count=0users.eachdo|user|count+=1ifuser.admin?endcountend

defcount_admin(users)users.count(&:admin?)end

defuser_names(users)names=[]users.eachdo|user|names<<user.nameendnamesend

defuser_names(users)users.map(&:name)end

nested_array=[[1,2,3],[4,5,6]]mapped_array=nested_array.map{|array|array.map{|n|n*10}}# => [[10, 20, 30], [40, 50, 60]]flat_array=mapped_array.flatten# => [10, 20, 30, 40, 50, 60]

nested_array=[[1,2,3],[4,5,6]]flat_array=nested_array.flat_map{|array|array.map{|n|n*10}}# => [10, 20, 30, 40, 50, 60]

numbmers_and_nil=[1,2,3,nil,nil,6]only_numbers=numbmers_and_nil.reject(&:nil?)# => [1, 2, 3, 6]

numbers_and_nil=[1,2,3,nil,nil,6]only_numbers=numbers_and_nil.compact# => [1, 2, 3, 6]

# mapとcompactを組み合わせて偶数の要素だけ値を10倍する（奇数は要素から除外）[1,2,3,4,5].map{|n|n*10ifn.even?}.compact#=> [20, 40]

# filter_mapを利用して偶数の要素だけ値を10倍する（奇数は要素から除外）[1,2,3,4,5].filter_map{|n|n*10ifn.even?}#=> [20, 40]

defcontains_nil?(users)users.eachdo|user|returntrueifuser.nil?endfalseend

defcontains_nil?(users)users.any?(&:nil?)end

puts"empty!"ifusers.size==0

puts"empty!"ifusers.empty?

first_user=users[0]last_user=users[users.size-1]

first_user=users.firstlast_user=users.last

users[rand(users.size)]

users.sample

counter=0users.eachdo|user|puts", "ifcounter>0putsuser.namecounter+=1end

users.each_with_indexdo|user,counter|puts", "ifcounter>0putsuser.nameend

counter=1users_with_index=users.mapdo|user|[counter,user]counter+=1end

users_with_index=users.map.with_indexdo|user,counter|[counter+1,user]end

users_with_index=users.map.with_index(1)do|user,counter|[counter,user]end

defnumbers_text(numbers)text=''numbers.each_with_indexdo|number,i|text+=', 'ifi>0text+=number.to_sendtextend

defnumbers_text(numbers)numbers.join(', ')# [1, 2, 3] => "1, 2, 3"end

defoldest_user(users)oldest=nilusers.eachdo|user|oldest=userifoldest.nil?||user.age>oldest.ageendoldetend

defoldest_user(users)users.max_by(&:age)end

defadmin_names(users)ret=[]users.eachdo|user|ret<<user.nameifuser.admin?endretend

defadmin_names(users)users.each_with_object([])do|user,names|names<<user.nameifuser.admin?endend

defadmin_names(users)users.filter_mapdo|user|user.nameifuser.admin?endend

names=%w(Alice Bob Carol)users={}names.eachdo|name|users[name]=find_user(name)end

names=%w(Alice Bob Carol)users=names.to_hdo|name|# 最初の要素がキー、2番目の要素が値となる配列をブロックの戻り値として返す[name,find_user(name)]end

names=%w(Alice Bob Carol)# 以下はちょっと古い書き方# mapとto_hを組み合わせて使うusers=names.mapdo|name|[name,find_user(name)]end.to_h# each_with_objectを使うusers=names.each_with_object({})do|name,h|h[name]=find_user(name)end

# number = [1, 2, 3]numbers=[1,2,3]

# def find_even_number(numbers)#   numbers.select(&:even?)# enddeffind_even_numbers(numbers)numbers.select(&:even?)end

# reserve=予約する(動詞)、reserved=予約済みである(形容詞)# chair.reserve?chair.reserved?# => false# chair.reserved('Tom')chair.reserve('Tom')chair.reserved?# => true

defhello(name)puts"Hello,#{name}!"endhello("Alice")

$ ruby hello.rbHello, Alice!

require'./hello'hello("Bob")

$ ruby runner.rbHello, Alice!Hello, Bob!

defhello(name)puts"Hello,#{name}!"endhello("Alice")# ←requireしたときにこの行が実行される

defhello(name)puts"Hello,#{name}!"endif__FILE__==$0hello("Alice")end

$ ruby runner.rbHello, Bob!

$ ruby hello.rbHello, Alice!

defhello(name)puts"Hello,#{name}!"end# __FILE__と$0の中身を確認するputs"#{__FILE__} |#{$0}"if__FILE__==$0hello("Alice")end

$ ruby hello.rb hello.rb | hello.rbHello, Alice!$ ruby runner.rb /your-path/to/hello.rb | runner.rbHello, Bob!!

defhello(name)puts"Hello,#{name}!"endif__FILE__==$PROGRAM_NAMEhello("Alice")end

$ gem install active_support

require'active_support/all'nil.blank?# => true

ifparent.children&&parent.children.singleton?singleton=parent.children.firstsend_mail_to(singleton)end

# childrenがnilならtry(:singleton?)はnilを返す# nilでなければ、children.singleton?が普通に呼ばれるifparent.children.try(:singleton?)singleton=parent.children.firstsend_mail_to(singleton)end

# Stringname=nilname.blank?# => truename=""name.blank?# => truename=" "name.blank?# => truename="Tom"name.blank?# => false# Arraynumbers=nilnumbers.blank?# => truenumbers=[]numbers.blank?# => truenumbers=[1,2,3]numbers.blank?# => false# Hashparams=nilparams.blank?# => trueparams={}params.blank?# => trueparams={name:"Tom",email:"hoge@hoge.com"}params.blank?# => false

# Stringname=""name.present?# => falsename="Tom"name.present?# => true

ifuser.name.blank?name="What's your name?"elsename=user.nameend

name=user.name.presence||"What's your name?"

name=""putsname.presence||"What's your name?"# => What's your name?

# Newsが1件でも存在すればメール送信＆ツイート発信good_news=company.good_newsifgood_news.count>0send_mail(good_news)tweet(good_news)end

ifgood_news=company.good_news.presencesend_mail(good_news)tweet(good_news)end

# nameがnilや空文字列（""）だったらメッセージを表示したくないname=blog.user.nameifname.present?show_message("Hello,#{name}!")end

ifname=blog.user.name.presenceshow_message("Hello,#{name}!")end

ifuser# userがいれば、何かを実行する# =>「もしuserがいれば」ではなく「もしuserなら」と読めてしまうendunlessusers.empty?# usersが空ではないなら、何かを実行する# => empty?の逆がないので、否定形で条件を書かざるを得ないend

ifuser.present?# userがいれば、何かを実行する# =>「もしuserがいれば」と明示的に読めるendifusers.present?# usersに1つ以上の要素があれば、何かを実行する# => 肯定形で条件が書けるend

ifemail.nil?# => emailが "" なら入力済みとして扱われてしまい、コールされないputs"Please input email!"end

ifemail.blank?# => emailが "" や " " の場合でも未入力と扱われるので、コールされるputs"Please input email!"end

defadmin_usersUser.all.select(&:admin?)end

defadmin_usersUser.where(admin:true)end

defadmin_user_idsUser.where(admin:true).map(&:id)end

defadmin_user_idsUser.where(admin:true).pluck(:id)end

defbuild_userUser.new.tapdo|user|user.email="hoge@hoge.com"user.name="Taro Yamada"endend

defbuild_userUser.newdo|user|user.email="hoge@hoge.com"user.name="Taro Yamada"endend

Date.current# => Tue, 05 Nov 2013Date.yesterday# => Tue, 04 Nov 2013Date.tomorrow# =>  # => Tue, 06 Nov 2013

Date.current# => 2013-11-052.years.ago# => 2011-11-05 06:21:40 +09002.years.since# => 2015-11-05 06:21:40 +09002.months.ago# => 2013-09-05 06:21:40 +09002.months.since# => 2014-01-05 06:21:40 +0900

date=Date.current# => 2013-11-05date.yesterday# => 2013-11-04date.tomorrow# => 2013-11-06date.prev_day# => 2013-11-04date.next_day# => 2013-11-06date.prev_day(2)# => 2013-11-03date.next_day(2)# => 2013-11-07date-2.days# => 2013-11-03date+2.days# => 2013-11-07date.ago(2.days)# => 2013-11-03date.since(2.days)# => 2013-11-07date.prev_month# => 2013-10-05date.next_month# => 2013-12-05date.prev_month(2)# => 2013-09-05date.next_month(2)# => 2014-01-05date-2.months# => 2013-09-05date+2.months# => 2014-01-05date.months_ago(2)# => 2013-09-05date.months_since(2)# => 2014-01-05date.ago(2.months)# => 2013-09-05date.since(2.months)# => 2014-01-05

date=Date.current# => 2013-11-05date.beginning_of_month# => 2013-11-01date.end_of_month# => 2013-11-30date.beginning_of_day# => 2013-11-05 00:00:00 +0900date.end_of_day# => 2013-11-05 23:59:59 +0900datetime=Time.current# => 2013-11-05T06:43:53+09:00datetime.beginning_of_hour# => 2013-11-05T06:00:00+09:00datetime.end_of_hour# => 2013-11-05T06:59:59+09:00

time=Time.current# => Mon, 23 Nov 2015 16:45:23 JST +09:00# その日の始まりと終わりの日時を取得time.all_day# => Mon, 23 Nov 2015 00:00:00 JST +09:00..Mon, 23 Nov 2015 23:59:59 JST +09:00# その日から見た月の始まりと、月の終わりの日時を取得するtime.all_month# => Sun, 01 Nov 2015 00:00:00 JST +09:00..Mon, 30 Nov 2015 23:59:59 JST +09:00# その日から見た年の始まりと、年の終わりの日時を取得するtime.all_year# => Thu, 01 Jan 2015 00:00:00 JST +09:00..Thu, 31 Dec 2015 23:59:59 JST +09:00

date=Date.current# => 2013-11-05date.tuesday?# => truedate.prev_week(:monday)# => 2013-10-28date.next_week(:monday)# => 2013-11-11

# キャメルケースにする"my_book".camelize# => "MyBook"# アンダースコア区切り(スネークケース)にする"MyBook".underscore# => "my_book"# ダッシュ(ハイフン)区切りにする"my_book".dasherize# => "my-book"# 複数形にする"book".pluralize# => "books""person".pluralize# => "people""fish".pluralize# => "fish""book_and_person".pluralize# => "book_and_people""book and person".pluralize# => "book and people""BookAndPerson".pluralize# => "BookAndPeople"# 単数形にする"books".singularize# => "book""people".singularize# => "person""books_and_people".singularize# => "books_and_person""books and people".singularize# => "books and person""BooksAndPeople".singularize# => "BooksAndPerson"# 人間が読みやすくする(一文字目は大文字 + スペース区切り)"my_books".humanize# => "My books"# タイトル形式にする(各単語の一文字目が大文字 + スペース区切り)"my_books".titleize# => "My Books"# クラス名にする(キャメルケース + 単数形)"my_book".classify# => "MyBook""my_books".classify# => "MyBook"# テーブル名にする(アンダースコア区切り + 複数形)"my_book".tableize# => "my_books""MyBook".tableize# => "my_books"

"    My\r\n\t\n   books       ".squish# => "My books"

"index,new,create".split(',')# => ["index", "new", "create"]

"index,new,create".split(?,)# => ["index", "new", "create"]

defprocess_usersusers.eachdo|user|process_user(user)endenddefprocess_user(user)send_mail_to(user)user.mail_sent_at=Time.nowuser.saveend

defprocess_usersusers.each(&method(:process_user))enddefprocess_user(user)send_mail_to(user)user.mail_sent_at=Time.nowuser.saveend

defdestroy_aged_admins(users,limit_age)users.select{|user|user.admin?&&user.age>limit_age}.each(&:destroy)end

defdestroy_aged_admins(users,limit_age)aged_admin=->(user){user.admin?&&user.age>limit_age}users.select(&aged_admin).each(&:destroy)end

defdestroy_aged_admins(users,limit_age)aged_admins=users.select{|user|user.admin?&&user.age>limit_age}aged_admins.each(&:destroy)end

!!nil# => false!!false# => false!!0# => true!![]# => true!!true# => true

nil.!.!# => falsefalse.!.!# => false0.!.!# => true[].!.!# => truetrue.!.!# => true

puts"User exists!"ifuser.nil?.!puts"Some users exist!"ifusers.empty?.!