Agenda

  1. class_eval & instance_eval
  2. method_missing
  3. Module as a namespace
  4. Gems
  5. require vs load
  6. $LOAD_PATH

class_eval

  1. 首先class_eval是只有类才能调用的，Class#class_eval
  2. class_eval会重新打开当前类的作用域
# class_eval
class User
end
User.class_eval do
  attr_accessor :name
  def hello
    "hello"
  end
end
user = User.new
user.name = "world"
puts user.name
puts user.hello


# module"s self
module Management
  def self.track
    "track"
  end
end
class User
  include Management
end
# User.track # => error
Management.track


# class_eval in project
# requirement: we need to execute a class method when module included
module Manegement
  def self.included base #Manafement模块被其他类Included的时候会执行
    base.extend ClassMethods #User类注入ClassMethod
    base.class_eval do #打开User类
      setup_attribute
    end
  end
 # Manegement 内部模块 当引入Management的时候 会被引用为其他类的类方法
  module ClassMethods
    def setup_attribute
      puts "setup_attribute"
    end
  end
end
class User
  include Manegement #目的是在include Management 的时候执行一些方法或者设置
end

instance_eval

  1. instance_eval 是所有类实例的方法
  2. 打开的是当前实例作用域
# instance_eval, instance methods and class methods
# 1. as a question
class User
end
User.class_eval do
  def hello
    "hello"
  end
end
User.instance_eval do
  def hi
    "hi"
  end
end
puts User.hi
user = User.new
puts user.hello
# puts user.hi #报错

# instance_eval, singleton_method
a = "xxx"
a.instance_eval do
  def to_hello
    self.replace("hello")
  end
end
puts a.to_hello
# b = "world"
# b.to_hello # => error

# class_eval as instance_eval
class User
end
User.class_eval do
  def hello
    "hello"
  end
  # works same as instance_eval
  def self.hi
    "hi"
  end
end
puts User.new.hello
puts User.hi

method_missing

  1. 当当前作用域上下文没有找到方法时就会调用
  2. method_missing方法
# metho missing
#
# 1. how it works
# 2. ancestors
# 3. rails"s AR
class User
  def hello
    "hello from User"
  end
  def method_missing(name, *args)
    "method name is #{name} ,parameters :#{args}"
  end
end
user = User.new
puts user.hello
puts "-" * 30
puts user.hi("hello",19)

Namespace

  1. Module
  2. Class
  3. Constants

使用::来访问

# module as a namespace
module Management
  COMPANY_NAME = "Hello World Company"
  module Track
    def track
      "track from Track module"
    end
  end
  class User
    def hello
      "hello from User class"
    end
  end
end
puts Management::COMPANY_NAME
puts "-" * 30
include Management::Track
puts track

Gems

  1. Ruby的包管理工具，类似于linux的rpm,deb,python的pip,Node的npm,c#的nuget
  2. 社区中Gem包涵盖了各方面开发所需要的工具和组件
  3. 通过gem命令来安装

gem命令

  1. gem list
  2. gem install
  3. gem uninstall
  4. gem sources

关于墙内安装问题，可以使用ruby china的镜像地址

gem sources --add https://gems.ruby-china.org/ --remove https://rubygems.org/

bundle gem

  1. gem本身会有版本依赖问题
  2. bundle是一个gem，被用来管理其他gems
  3. bundle类似于linux的yum apt等等，是一个gems关系管理工具

bundle的基本使用

  1. gem install bundler
  2. Gemfile 文件
  3. bundle install/update/show/list

require vs load

相同点

  1. 都会在$LOAD_PATH下面查找当前要引入的文件

不同点

  1. require 调用文件时不需要.rb的文件后缀，而load需要
  2. require 针对童谣的文件只会调用一次，而load会反复调用
# require vs load
# 1. print require and load result
# require "net/http"
puts require "net/http" # => true
puts require "net/http" # => false
# puts load "net/http.rb"
puts Net::HTTP

$LOAD_PATH

  1. ruby代码的查找路径为当前的$LOAD_PATH环境变量
  2. ruby文件名命名规则: 文件的名字代表了当前 class/module的名字
# load_path
# require "track"