Ruby on Rails Tutorial fourth the other data types of ruby behind Rails

1. Arrays and Ranges

2, Block

Convention: Use curly braces when there is only a single line of code in the block, when the block is a long line of code, or when there are many rows using do. End form. For example:

>> (1..5).each{|i| puts 2*i}
(1..5).each do |i|
     Puts 2*i
     Puts ‘-‘
End
>> 3.times{puts "betelgeuse"}
>> (1..5).map{|i| i**2}
>> %w[a b c].map{|char| char.upcase}
>> %w[A B C].map{|char| char.downcase}
>> %w[A B C].map(&:downcase)
>> (‘a‘..‘z‘).to_a.shuffle[0..7].join #Generate a random second-level domain name

3. Hashes and symbols

A hash is essentially an array, and its index is not limited to numbers. The index of the hash can use any object. A hash is represented by a pair of curly braces that contains some key-value pairs. The biggest difference between hashes and arrays is that hash elements do not have a specific order. Hash the value of a key that is not defined is nil

>> user={} #{} is an empty hash
>> user["first_name"]="Amy"
>> user["last_name"]="Sun"
>> user["first_name"]
=> "Amy"
>> user
=> {"first_name"=>"Amy","last_name"=>"Sun"}
>> user["e-mail"]
=> nil

>> user={ "first_name"=>"Amy","last_name"=>"Sun" }
=>{"first_name"=>"Amy","last_name"=>"Sun"}

symbol : A unique data type in Ruby, a string with no constraints

>> user={ :name=>"AmySun",:email=>"12***22@**.com" }
=> {:name=>"AmySun",:email=>"12***22@**.com"}
>> user[:name]
=> "AmySun"
>> user[:password]
=> nil

>> h1={ :name=>"AmySun",:email=>"12***22@**.com" }
=> {:name=>"AmySun",:email=>"12***22@**.com"}
>> h1={ name:"AmySun",email:"12***22@**.com" } #:name=> Same as name:, so { :name=>"AmySun" } and { Name: "AmySun" } is equivalent, but only: name indicates the symbol
=> {:name=>"AmySun",:email=>"12***22@**.com"}
>> h1==h2
=> true

Nested hashes

>> params={}
=> {}
>> params[:user]={ name:"AmySun",email:"12***22@**.com" }
=> {:name=>"AmySun",:email=>"12***22@**.com"}
>> params
=> {:user=>{:name=>"AmySun",:email=>"12***22@**.com"}}
>> params[:user][:email]
=> 12***22@**.com

Each method of hash

>> user={ success:"It worked!",danger:"It failed." }
=> {:success=>"It worked!",:danger=>"It failed."}
User.each do |key,value|
     Puts "Key #{key.inspect} has value #{value.inspect}"
End
# Result
# Key :success has value "It worked!"
# Key :failed has value "It failed."

Where the inspect method returns the string literal representation of the called object, for example:

>> puts (1..5).to_a.inspect
[1,2,3,4,5]
>> puts :name,:name.inspect
Name
:name
>> puts "It worked!","It worked!".inspect
It worked!
"It worked!"
>> p :name # is equivalent to ‘puts :name.inspect’
:name 

4. Introduction of CSS Instructions

' Application ', media:'all','data-trubolinks-track'=>true% >

Description: When calling a function, if the hash is the last argument, you can omit the curly brace, because Data-trubolinks-track has hyphens, so it cannot be written as Data-trubolinks-track: The true style generates HTML source code as follows:

<link data-trubolinks-track="true" href="/assets/application.css " media="alll" rel="stylesheet "/>

Ruby on Rails Tutorial fourth the other data types of ruby behind Rails