symbol

change string to symbol:

use to_sym or intern

ex:

"test".to_sym

--->  :test

change symbol to string

method 1: use to_s

method 2: use #{ }

ex:

"#{:abc}"

---> "abc"

methods

methods:

A.methods:

show class methods

A.methods(false):

only show class methods of A, not including inherited methods

a.methods:

show instance methods of a

instance_methods:

A.instance_methods equals a.methods

A.instance_methods(false):

show only instance_methods 0f A, not including inherited methods

private_methods, public_methods, protected_methods, singleton_methods

compare: equal?, Comparable module

check  whether  two objects are the same object

define how to compare

use Comparable module & define <=> method

the return value of method <=> ,  1, 0 , & -1 decides greater than, equal than, & less than

ex:

class Rabbit

     include Comparable 

     attr_accessor  :name

     def  <=> (other_rabbit)

          if  self.name <>

                  -1

          elsif  self.name > other_rabbit.name

                  1

          else

                  0

          end 

     end

end

if the thing to compare know how to compare, there is a shorter definition

ex:

def  <=> (other_rabbit)

       self.name<=> other_rabbit.name

end

true, false & nil

In Ruby, nil & false  are the only two objects have boolean value of false

for, each

for

ex:

for a in [1,2,3]

puts a

end

each

ex:

[1,2,3].each do |i|

puts i

end

loop, while, until

loop

ex:

loop do

    a=a+1

    break if a>3

end

loop do 

     a=a+1

     next if a <3

     break

end

while

ex:

while a<3

end

until:

ex:

until a>3

end

case

ex:

case  name

when "peter"

puts "peter"

when "andy"

puts  "andy"

else

puts  "others"

end

how it works

translate to 

if "peter" === name

note: the === method can be customarily defined

private & protected methods

private method:

(1) use private  with argument

ex:

private  :test,  :run

(2) use private

ex:

private

def  test

end

def run 

end

the methods after private are private

protected method:

use protected

can call the object's protected method as long as self is an instance of the same class  as the object whose protected method is called

global variable

start with $

built-in global variables:

$: the directories that make up the path Ruby searches for external file

$0: name of the file Ruby is executing

$$: process id of Ruby process

ps:  use English.rb to replace these built-in global variables with meaningful names

instance variable

In the class definition, the instance variable insides method & outside method are not the same

the instance variable inside method belongs to object

the instance variable outside method belongs to class

class & self

In the class definition, self = class

so Rabbit.run = self.run

In the class-method definition,  self = class

:: access

(1) access constant

(2) access nested class

ex:

module ActionController

       module  Routing

              class Route

....

end

ActionController::Routing::Route.new

ex:

class  Rabbit <>

end

class ApplicationController <>

end

(3) access nested module

method_missing

If the message sent to object is the message object can't understand, it will trigger execution of method_missing

Rails use method_missing to look up database & create methods 

super keyword

call the method of superclass or module

ex:

class A

    def test(num)

           puts "A test #{num}"

    end

end

class B  <>

     def test( num)

           super

   puts "B test #{num}"

     end

end

b= B.new

b.test(2)

--->  A test 2

         B  test 2

super will pass the parameters to superclass or module

another usage:  call super will parameters to pass specific parameters

root module & root class

root class:  Object

root module:  Kernel

attr_reader, attr_writer,

the getter:

ex:

attr_reader  :name

the setter:

ex:

attr_writer :name

getter & setter:

ex:

attr_accessor :name

respond_to?

check if the object has specific method

ex:

test.respond_to?("methods")

---> true

object_id

Object's method

return the id of the object

ex:

a=3

b=a

now a & b have the same object id 

the data controller can access

CGI data:

access @params  via params method

ex:

params[:id],  params[:user][:age]

session information:

access @session via session method

ex:

session['user']

model's data

ex: 

model Car has a name field

car is an instance of model Car

car.name

mysql command

start mySQL:

sudo /usr/local/mysql/bin mysqld_safe

stop mySQL:

sudo /usr/local/mysql/bin mysqladmin shutdown

create an account for a database:

grant  all on *.*  to 'deeplove'@'localhost'  identified by  '111';

create new user account "deeplove", with password 111, 

connect to database from "localhost", all  means you can do anything( SELECT, INSERT, ...)

*.* means you can connect to every database ( Dog.* means you can only connect to Dog database)

join:

collect information from two or more tables & present it as a single table

left join  ...  on ...  :

return all matching rows from first table, even if there are no matching rows in the second table

group by

combine two tables using the filed both tables have 

select syntax

select columns from table where condition

rails source code location in mac

/Library/Ruby/Gems/1.8/gems/rails-2.0.2

/Library/Ruby/Gems/1.8/gems/actionpack-2.0.2/lib

action_controller.rb & action_view.rb are in this folder

/Library/Ruby/Gems/1.8/gems/activerecord-2.0.2

require vs load

ex:

require  'test'

require  'test'

second require is useless

ex:

load  'test'

load  'test'

second load will load test again 

puts and print

puts will print new line

print will not

gets

get a line of input( in string)

paginate

divide large collections into pages

ex:

in the controller:

def  car_list

     @car_pages,  @cars = paginate ( :cars,  :order_by => 'name')

end

@car_pages is a paginator object.

@cars contain 10 rows.  ( default is 10 rows)

in the view:

table

  for car in @cars

       tr  td  car.name  td  tr

  end

table

hr

   pagination_links(@car_pages) 

hr

pagination_links  show the current page, two page numbers on either side of current page, first page & last page 

helper

remove the logic from view to helper

ex:

module   TestHelper

              def  run

                       "test_title"

              end

end

in the test controller

<%=  run  %>

originally the function in the helper file can only be accessed by related view,

but there is method for sharing helper

sharing helper:

method 1:

define the method in application_helper.rb

method  2:

ex:

add  TestHelper  to controller

helper  :test

h( )

escape html tag

ex:

<%= "<b>test</b>"% >

show test in bold

<%= h("<b>test</b>") %>

show  <b%>test</b>

xml template

builder template:

xml builder:

xml.tagName

ex:

xml.productName ( "car")

-->   <productName>car</productName>

cache

the page is cached .

Hence,  after first request, the same URL's response is deliver from cache, rails is no involved 

3 caches:

page caching,  action caching  & fragment caching

page caching:

ex:

caches_page  :test

action caching:

execute filter before return cached pages

ex:

before_filter  :test_filter

caches_action  :test2

turn on caching( in environment.rb) :

ActionController::Base.perform_caching = true

removing cache:

expire_page

ex:

expire_page  :action=>test

expire_action:

ex:

expire_action :action=>test2

sweeper:

observe the model. When the model is changed, the sweeper expire the cached pages that 

depend on the model

ex:

in app/models

class  TestSweeper <>

         observe  Car

         def  after_create(car)

                   expire_car_page

         end

end

in app/controllers

class Test <>

    cache_sweeper  :test_sweeper

end

the location to store cached pages:

ex:

http://localhost:3000/content/show/1  is stored in app/public/content/show/1.html

verification

verify that certain conditions are met

verify:

ex:

verify   :session => :user_id,

             :add_flash => { :note=> "you are wrong" }

             :redirect_to => index

if the session does not contain key :user_id,  

a note is added to flash & request is redirected to index

redirect_to

three forms:

1. redirect_to ( options ... )

ex:

redirect_to (:action=>jump)

2. redirect_to (path)

ex:

redirect_to ("/test/run")

show /view/test/run.html.erb

3. redirect_to( url)

ex:

redirect_to("http://www.google.com")

logger

4 levels:

warn,  info,  error,  fatal

ex

logger.warn("invalid number")

log file:

/log/development.log,  /log/test.log,  /log/production.log

group controllers into module

For example,  two directories  Test1  & Test2,
controller Rabbit1Controller in Test1,  Rabbit2Controller in Test2

url_for( :controller=> "rabbit1", :action=>"jump")
--->  http://localhost:3000/test1/rabbit1/jump

rails program load sequence

ex:  http://localhost:3000/rabbit/list

when getting request above, the load sequence is as follows:

1. load rabbit_controller.rb

2. instantiate an object of class RabbitController

3. look in app/helpers for rabbit_helper.rb.

    If found, the module RabbitHelper is mixed into RabbitController

4 look in app/models for rabbit.rb. If found, load it

define the models used in controller:

ex:

model  :car,  :clothes

define the observers used in controller:

ex:

observer   :car_observer

define the model used in controller 

flash

the value stored in the flash in the first request is available in the second request.

After processing 2nd request, the value is removed from flash

main use:

error message

ex:

def  test

    flash[:note] = "error"

    redirect_to :action=>test2

end

test2.html.erb

<%= @flash[:note] %>

session & cookie

controller action, view tempelate, render

controller裡定義的action(method)會對應到view下的templelate

例如index對應到index.html.erb

所以如果controller要做的action是index，

browser顯示的網頁即是index.html.erb

為何action是index，即顯示index.html.erb ?

一般在controller定義的action，

例如index，

預設都會呼叫如下的render 指令，

所以controller在做index action時，

即會顯示index.html.erb

render command:

ex:

render :template => “test/index”

顯示 view/test/index.html.erb

:template後接的path是相對於view

如果改成:file，之後的path是絕對路徑

如果render顯示的是另一個page，

改變的是顯示的內容，

URL還是原page的URL，

若要連URL一起改變，

要代用redirect_to

ex:

render  :action=>”index”

顯示 index.html.erb

(注意render不會做action，只會顯示頁面，

若要做action，要用redirect_to) 

ex:

render :text=> “hello”

顯示hello

:status

ex:

render  :status=>404

html response的status

可以不定義action，但一定要定義顯示的頁面

例如index action沒定義，

但index.html.erb有定義，

則browser還是可以顯示正確的頁面。

the instance variable of the controller is available in the template

the template can access instance variable set in the controller action. Hence, rabbit's view can access dog's controller's instance variable if it is triggered from dog's action

form helper

form_tag:   和model無關

ex:

<% form_tag do %>

<p><label for=”login”>Login</label>

<%= text_field_tag  ‘login’ %></p>

<p><%= submit_tag ‘Log in’ %> </p>

<% end %>

1.如果form_tag後沒有接action，那麼action就是form目前所在的

  頁面對應到的method

2存取使用者輸入的資料，例如param, such as params[:login], log對應

  到text_filed_tag的值

ex:

<% form_tag  :action=>'play'  do %>

<p><label for=”login”>Login</label>

<%= text_field_tag  'car',  ‘login’ %></p>

<p><%= submit_tag ‘Log in’ %> </p>

<% end %>

1. text_field_tag後接的car是model name，login是car的attribute

   , the controller can access it using  params[:car][:login]

submit_tag 後接的字串是submit button上的文字

form_for : 和model有關

ex:

 <% form_for :person, @person, 

    :url => { :action => "create" } do |f| %>

      <%= f.text_field :first_name %>

      <%= f.text_field :last_name %>

      <%= submit_tag 'Create' %>

  <% end %>

對應的html

 <form action="/persons/create" method="post">

      <input id="person_first_name" name="person[first_name]" size="30" type="text" />

      <input id="person_last_name" name="person[last_name]" size="30" type="text" />

    <input name="commit" type="submit" value="Create" />

    </form>

存取使用者輸入的資料:

以上面為例子，Person.new(params[:person] )

ex:

<% form_for :rabbit ,  url=>{ :controller=>:rabbit, :action=>create},

      :html=> {:id=>’peter’ } do |t| %>

對應的html

<form action="/rabbit/create" id="peter" method="post">

text_field & text_field_tag

regular form helper is usually end with tag

model form helper is usually not end with tag 

ex:

text_field :customer, :name

create customer in the action of controller:

@customer = Customer.new(params[:customer])

text_field:

hidden_field:

password_field:

text_area:

radio_button(:variable, :attribute,  tag_value,  options):

check_box:

select:

selection list

ex:

save & save!

save object into database

save! will raise a exception if the save is not successful 

save only return false when save is not successful 

update_attributes, updat & update_all, save

update column of table

update will change the state of object and database

update_attributes

ex:

rabbit.update_attributes( :name=> "peter",  :age=> 13)

update

ex:

Rabbit.update( 5, :name=>"peter", :age=>13)

update rabbit with id =5

update_all:

Rabbit.update_all(:name=>"peter")

all rabbits' names become "peter"

use save:

ex:

rabbit.name="peter"

rabbit.save

use save to update database

find method in rails

without dynamic find_by_all

@task = Task.find( :all, :conditions=> [‘complete= ?’ ,false] )

with dynamic find_by_all

@task = Task.find_all_by_complete(false)

without dynamic find_by

@task = Task.find( :first, :conditions=> [‘complete= ?’ ,false],

                                :order=>’created_at DESC’ )

with dynamic find_by

@task = Task.find_by_complete(false,   :order=>’created_at DESC’)

find by id

find( params[:id], :conditions=>[“name=?”, “peter” ] )

find through association

ex:

project has many tasks

task belongs to project

without association:

@task = Task.find(:all, :conditions=> [ ‘proect_id=? AND complete =?’  , @project_id,  false] )

with association:

@project = Project.find(params[:id])

@task = @project.tasks.find(:all,     :conditions=>[‘complete=?’,   false])

or

@task = @project.tasks.find_all_by_complete(false) 

find method in model

將find method定義在model比較好

ex:

Task的model

def  self.find_incompletet 

    find_all_by_complete(false, :order=>’created_at DESC’ )

end    

 注意: 此find method要定義成class method

          到時候可呼叫 @project.tasks.find_incomplete

          若定義成instance method，則會error

find_by_sql:

use sql syntax in the find_by_sql

pros:  faster

ActionMailer & gmail

use ActionMailer to send email ( with gmail)

ex:

require 'rubygems' 

require 'action_mailer' 

require 'smtp_tls'

class Emailer <>

  def test_email(email_address, email_body) 

    recipients(email_address) 

    from "peter@gmail.com" 

    subject "This is a test e-mail" 

    body email_body 

  end 

end

ActionMailer::Base.smtp_settings = { 

  :address => "smtp.gmail.com", 

  #25 ,465

  :port => 587, 

  #:domain => "localhost.localdomain",

  :authentication => :plain, 

  :user_name => "peter", 

  :password => "xxxxxx", 

}

Emailer.deliver_test_email('jack@yahoo.com', 'this is a test email')

smtp_tls is for sending email from gmail

send by gmail in rails:

1. add smtp_tls.rb in configure directory

2. add  require 'smtp_tls'  in environment.rb

access table's column in the model

ex:

the table rabbits has column  name

the model  rabbit can access name by  self.name

before_create

like before_filter,  but before_create is used in the model

is executed when the record is created

filter

define the actions to do before(after) some actions

two define syntaxes:

1. use method to define filter

2. use class to define filter

before_filter:

define the actions to do before some actions

ex:

before_filter :check

do check before any action. 

If check return false,  the action is not done

after_filter:

define the actions to do after some actions

filter & inheritance :

B extends A, then A's filter is done first, then B's filter is done

filter's scope:

only for some actions:

ex:

before_filter :check,  :only=>:index

before_filter :check,  :only=>[:index,  :new]

not for some actions:

before_filter :check,  :except=>:index

around_filter:

the combination of before_filter & after_filter

ex:

class TestFilter

    def  before(controller)

         @name="peter"

    end

    def  after(controller)

         @name ="andy"

    end

end

around filter  TestFilter.new

mongrel

a web server 

faster than WEBrick

install:

sudo gem install mongrel

start:

mongrel_rails  start

start options:

-d:  run in background 

-e:  rails environment to run

stop:

mongrel_rails stop

restart:

mongrel_rails restart

link

link to css

stylesheet_link_tag   'test'

test.css is in /public /stylesheets

link to image

image_tag  'test.jpg'

test.jpg is in  /public/images

link to page

link_to  "go to" ,  :controller=>"test", :action=>"index"

link to javascript:

javascript_indclude_tag  :defaults

link to prototype, effects, dragdrop, controls, application in /public/javascripts

url_for:

generate url according to route.rb

ex:

url_for ( :controller=>"rabbit", :action=>jump )

-->  http://localhost:3000/rabbit/jump 

layout

the layout for all website:

method 1:

use application.html.erb, it is the layout for all website

method 2:

ex:

define the layout test.html.erb

add following line to app/controllers/application.rb

layout "test"

yield:

render the template.  The template is rendered at this location within layout

layout can access variable defined in the template 

rails routing

config/route.rb

set the page of webSite root:

map.root  :controller => "test"

note: remember to remove  /public/index.html

default route

map.connect  ':controller/:action/:id'

map.connect  ':controller/:action/:id.:format'

ex: 

http://localhost:3000/test/apple/3.xml

test map to :controller,  apple map to :action, 3 map to :id, xml map to :format

the parameter get from default route:

params[:controller],  params[:action],  params[:id]

set controller & action:

map.connect  'test/:var',  :controller=>rabbit,  :action=>jump

ex: 

http://localhost:3000/test/apple

apple map to :var

:requirements

set the requirement the component must match

ex:

map.connect  ":day",  :requirements => { :day => /[0-3]?\d }

the pattern for remaining components in the URL ( not specify in the URL)

use * with a name

ex:

map.connect  "*anything",  :action=> "unknown_action"

named route:

replace map.connect with map.routeName,

replace  url_for with routeName_url

ex:

 map.run  :controller=>"test", :action=>"run"

 redirect_to (run_url)

 link_to(" run" , run_url )

generate command, rails command, rake command, console

rails:

rails -d mysql  test

create files for rails project, using mysql  

( default is sqlite)

generate:

script/generate  controller rabbit index 

create rabbit controller with index action,  rabbit test, rabbit helper  & index template in the rabbit view

rake:

rake db:migrate

create the table in the database based on the migration file

script/console:

-s:  Any modifications you make will be rolled back on exit

erube

deal with the file includes html & ruby code

install:

get eruby from  http://www.modruby.org/en/index.rbx/eruby/download.html

set link:

sudo ln -s /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/eruby /usr/local/bin/eruby

combine apache & erube:

set link:

     ln -s /usr/local/bin/eruby /Library/WebServer/CGI-Executables/eruby

edit /etc/apache2/httpd.conf

(1) red part

    
    AllowOverride None

    Options FollowSymLinks

(2) add following to 

    AddHandler rubypage .erb .rhtml

    Action rubypage /cgi-bin/eruby

run eruby:

eruby  test.html.erb

erb 

cgi

require 'cgi'

cgi's method name equals the tag it create

Hence, cgi.h1 create h1 tag

use + to combine the same level tag

ex:

cgi = CGI.new('html4')

cgi.out do

    cgi.html do

          cgi.head  do

                 "test head"

          end  +

          cgi.body do

                cgi.h1 {  "hello" } 

          end

    end

end

--->

<HTML><HEAD>test head </HEAD><BODY><H1>hello</H1></BODY></HTML>

cgi.params:

represent query string

ex:

http://localhost/cig-bin/test.cgi?name=peter&age=3

cgi.params =  { 'name'=>'peter',   'age'=>'3' }

send

dynamically call a method with unknown name

ex:

def  test_rabbit(name)

       puts name

}

a="rabbit"

send("test_#{a}", "peter")

---->  peter

1st parameter is method name,  second parameter is parameter

usage: get method from user input

note:

some_object.send(  function_name,  args )  is the same as 

some_object.function_name(args )

show message with debug

write to stand error

ex:

warn "error"  if ($DEBUG)

enable $DEBUG

ruby -d 

xml library

require 'rexml/document'

<=>

ex:

3 <=> 3

--->  0

3 <=> 4

---> -1

4 <=> 3

--->  1

test

require  'test/unit'

assert_equal

if two parameter are equal, return true

ex:

assert_equal("dd", "ee")

ri command

read the information about ruby API

ex:

ri  Test::Unit

alias

define another method name

ex:

alias  :puts_2  :puts

puts_2  “ hello”

--->  “hello”

system

call extern program 

ex:

System( “ls”)

method naming ( end with ? or ! )

method that returns true or false ends with ?

ex: 

empty?

method that changes the state of the object ends with!

ex: 

save!

built-in methods with !

upcase!,  chomp!,  sort!,  reverse!

change value to string( interpolation)

use  “#{  }”

ex:

a= 123

b= “#{a}”+ “4”

--->  b= “1234”

file methods

read  a file:

input_file =File.new (filename, ‘r’)

write a file:

output_file= File.new( filename, ‘w’)

‘w+’: 

read and write.  When creating the file, the old file is overwritten 

'a':

append

read:

return the content of the file in the string

readlines:

output_file.readlines()

return an array with each line of the file

puts:

output_file.puts(“hello”)

write “hello” to output_file

close:

output_file.close()

close the file

show the files and directories under directory:

ex:

Dir.open("Desktop").entries

---> [ "." , "..", "test.c", "book"]

directory?

ex:

File.directory?("test")

extname:

ex:

File.extname("test.exe")

--> ".exe"

environment variable

ENV[‘HOME’] (for unix-like)

ENV[‘HOMEDRIVE’]+ ENV[‘HOMEPATH’] (for windows)

return the path of home directory

ex:

on my mac , output is “/Users/Pan”

ARGV

the parameter to the ruby program

ex:

ruby test.rb  123

ARGV[0]  is 123

comment

start with #

=begin  & =end

use in multiple-line

if , else, elsif, unless

if and else:
ex:
if a==3
    puts “a==3”
else
    puts “a!=3”
end

elsif

use elsif,  not elseif

unless

if ! (x==1)  

equals

unless x==1

plugin install

install for ruby

remote install:

ex:

gem  install sqlite3-Ruby

local install:

ex:

1. get gem file from  http://rubyforge.org

2. gem install  scruffy-0.2.2.gem 

    ( in the directory with scruffy-0.2.2.gem)

install for rails project

remote install:

ex:

script/plugin  install  http://svn.techno-weenie.net/projects/plugins/acts_as_authenticated/

local install:

1. 用svn抓plugin下來

    ex:

    svn checkout http://svn.techno-weenie.net/projects/plugins/acts_as_authenticated/

2. 將plugin放到rails project下的vendor/plugins/

textmate & rails 2.0

install rails 2.0 bundle

1.  download rails 2.0 bundle  rails 2.0 bundle

2.  move rails 2.0 bundle to  Library/Application Support/TextMate/Bundles,

     rename the bundle as  Ruby on Rails.tmbundle

3.  reload bundle in textmate

4. mv Builder.rb Builder.rb.off   

    in  Applications/TextMate.app/Contents/SharedSupport/Support/lib

textmate shortcut

select word:

ctrl + w

show bundle list

ctrl + esc

select bundle item:

ctrl + command + t

show bundle editor:

ctrl + option+ command + b

ToDo bundle:

show ToDo list

ctrl + shift + t

Define TODO: ,  FIXME: ,  CHANGED:   in the comment of the file.

Then show ToDo list will find there lines in the files

html  bundle:

insert open & close tag with current word

ctrl + <

ex:

enter head, then with this short cut,  it becomes

ex:

enter this short cut, then enter abc, it becomes

wrap selection in open & close tag

ctrl + shift + w

ex:

enter hello, then enter this short cut,  then enter head, it becomes hello

tab completion :

1. head:   

    head+ meta + title

2. style:

3. script:

4. doctype:

insert a link(with the word in the clipboard)

ctrl + shift + L

webpage preview:

ctrl + option+ command + p

ruby  bundle:

run ruby program

command + r

# =>  mark

add # => mark

# + tab

execute the line with # => mark

ctrl + shift + command + e

find doc about the word

ctrl + h

tab completion :

1. cla :

    for class

2. def :

     for method

3.  r ,  w,  rw

     for attr_reader(),  attr_writer(),  attr_accessor()

4. while 

5.  if

6.  inj: 

     for inject

7. ea:

    for each

8. tim:

    for times

9. sorb:

    for sort_by

10. eawi:

      each_with_index

rubyOnRails bundel:

activate rubyOnRails bundle:

ctrl + option + shift + r + 3

params completion:

ctrl + p

session completion:

ctrl + j

call generate script:

ctrl + | + 1

tab completion:

for model: 

1. mccc 

    for model create column continue

2.  t.

     提示column type

3. mcol

    create column

visor : terminal access

1. install SIMBL

2. install visor

provides a systemwide terminal window accessible via a hotkey 

my hot key:  command + 1

date and time method

require 'date'

require 'time'

Time.now  or Time.new

-->  Fri May 02 16:50:08 +0800 2008

Time.now.strftime('%Y-%m-%d')

-->  "2008-05-02"

SECOND_IN_A_DAY

兩個時間相減得到的單位是秒 

Date.today:

%Y, %y:  year

%b, %B: month

%m : month(number)

%d, %e:  day of month

%a, %A: dat name( such as Tue)

%H, %I: hour

%M: minute

%S: second

%c:  equals "%a %b %d %H:%M:%S %Y"

%x:  equals "%m/%d/%y"

block and yield

yield: 

run what block defines

ex:

def  test(*args, &block)

        yield(*args)

end

test("hello"){ |i| puts i }

---> hello

note:

yield(*args)  = block.call(*args)

when defining a method that receives blocks,

there are two ways

(1)  define method with block arguments

ex:

def test( &block)

end

(2)define method without block arguments

ex:

def test

end

pass arguments to blocks

in the method definition, call yield with arguemtns

ex:

yield (a, b, c)

in the block, use | | to receive arguments 

ex:

| a, b, c|

return value from call block

the return value is last expression evaluated in block

ex:

in the method definition

a= yield

here doc

build up a long string

ex:

NAME= <<END_MY_STRING

      hello

      how are you

END_MY_STRING

puts NAME

--->   hello

         how are you

required, optional, default-valued parameters

required parameter:

def  test1( name)

end

default value parameter

def  test2(name=”peter”)

end

呼叫test2時，若是沒傳參數，則name=”peter”, 

若是傳參數”andy”，則name=”andy”

optional parameter

use *

ex:

def test(*abc)

end

abc可接受多個參數，以array表示

例如呼叫test(1,2)

則p abc 印出 [1, 2]

note: optional parameter must be last parameter of the method