Ruby10 Class Module Gem 深入

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 NetVERSION puts Track::Parser.parse