Rails源码阅读（四）gem_rubygems之require_Rails_require_深入理解（一）

Rails源码阅读（四）rubygems之require_Rails_require_深入理解

 

提出问题：

require的行为为何不同？

require 'pp' 其实是从加载路径中找到了pp这个文件并且加载

require 'active_support' 加载了active_support这个文件，但这个文件并没有在加载路径中的，如果你自己手动加载过active_support库，你一定会知晓这个了

 

irb(main):001:0> require 'active_support'
LoadError: no such file to load -- active_support
	from (irb):1:in `require'
	from (irb):1

 

基本知识：require的寻找方法

 

返回值： 

    require(string) => true or false    

    Ruby tries to load the library named string, returning true if successful.

寻找的路径：

    If the filename does not resolve to an absolute path, it will be searched for in the directories listed in $:.

寻找的文件格式：

    If the file has the extension ``.rb'', it is loaded as a source file;

    if the extension is ``.so'', ``.o'', or ``.dll'', or whatever the default shared library extension is on the current platform, Ruby loads the shared library as a Ruby extension.

    Otherwise, Ruby tries adding ``.rb'', ``.so'', and so on to the name.

不会重复加载；如何判断已经加载过了；加载的文件存储位置：

    The name of the loaded feature is added to the array in $". A feature will not be loaded if it's name already appears in $".

注意：

    However, the file name is not converted to an absolute path, so that ``require 'a';require './a''' will load a.rb twice.      

附：

    require "my-library.rb"     require "db-driver"

    require "directory1/directory2/directory3/xxx" #这样可以根据$:的相对路径寻找。

 

寻找答案： 

在1.9之前，加载gem库的话，需要先加载rubygems，也就是先执行 require 'rubygems' 这个语句。

加载前后，加载路径并没有什么变化，依然如下：

 

irb(main):005:0> pp $:
["/opt/ruby/lib/ruby/site_ruby/1.8",
 "/opt/ruby/lib/ruby/site_ruby/1.8/i686-linux",
 "/opt/ruby/lib/ruby/site_ruby",
 "/opt/ruby/lib/ruby/vendor_ruby/1.8",
 "/opt/ruby/lib/ruby/vendor_ruby/1.8/i686-linux",
 "/opt/ruby/lib/ruby/vendor_ruby",
 "/opt/ruby/lib/ruby/1.8",
 "/opt/ruby/lib/ruby/1.8/i686-linux",
 "."]

但是执行了require 'activesupport'语句之后，就有变化了

 

irb(main):005:0> require 'activesupport'
DEPRECATION WARNING: require "activesupport" is deprecated and will be removed in Rails 3. Use require "active_support" instead.. (called from /opt/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/activesupport.rb:2)
=> true

irb(main):006:0> pp $:
["/opt/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/vendor/i18n-0.1.3/lib",
 "/opt/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.5/bin",
 "/opt/ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib",
 "/opt/ruby/lib/ruby/gems/1.8/gems/builder-2.1.2/bin",
 "/opt/ruby/lib/ruby/gems/1.8/gems/builder-2.1.2/lib",
 "/opt/ruby/lib/ruby/gems/1.8/gems/memcache-client-1.8.5/bin",
 "/opt/ruby/lib/ruby/gems/1.8/gems/memcache-client-1.8.5/lib",
 "/opt/ruby/lib/ruby/gems/1.8/gems/tzinfo-0.3.27/bin",
 "/opt/ruby/lib/ruby/gems/1.8/gems/tzinfo-0.3.27/lib",
 "/opt/ruby/lib/ruby/site_ruby/1.8",
 "/opt/ruby/lib/ruby/site_ruby/1.8/i686-linux",
 "/opt/ruby/lib/ruby/site_ruby",
 "/opt/ruby/lib/ruby/vendor_ruby/1.8",
 "/opt/ruby/lib/ruby/vendor_ruby/1.8/i686-linux",
 "/opt/ruby/lib/ruby/vendor_ruby",
 "/opt/ruby/lib/ruby/1.8",
 "/opt/ruby/lib/ruby/1.8/i686-linux",
 "."]

这里可以推测，require方法做了某些特殊的处理。

请留意一下，当前路径即“.”路径在最后，这个设计是多么周到，想想看，为什么～

 

查看源码

ruby的require源码，只是个stub：

 

  def require(string)
    #This is a stub, used for indexing
  end

 

应该仔细阅读下注释，还是比较重要的：

#1 并不是只加载.rb文件，你知道么

#2 加载次数问题和名字问题

#3 怎么防止重复加载，防止的机制是什么

 

rubygems重载了require这个最基本的方法：

 

alias gem_original_require require

  def require(path) # :doc:
    gem_original_require path
  rescue LoadError => load_error
    if load_error.message =~ /#{Regexp.escape path}\z/ and
       spec = Gem.searcher.find(path) then
      Gem.activate(spec.name, "= #{spec.version}")
      gem_original_require path
    else
      raise load_error
    end
  end

 注释写的比较清楚，

#1 如果没有找到例如active_support，则使用Gem来activate，之后再require

#2 Gem来activate做了哪些事情呢：

     that gem is activated (added to the loadpath).

 

    所以这里改变了加载的路径

 

接下来要不要看看Gem做的事情呢。

应该的。不过可以推测一下，整体上还是做了些java世界里mvn做的一部分工作。

 

先占个位：

深入理解ruby安装，require，load，gem，等等

http://www.skorks.com/ #这个人不错阿，技术人的性格，deep into ruby！

http://www.skorks.com/2009/08/digging-into-a-ruby-installation-require-vs-load/

--deep into rails command line

http://www.skorks.com/2011/08/when-developers-go-to-great-length-to-save-typing-4-letters/

--deploy rails to tomcat 很好很强大for javaer

http://www.skorks.com/2010/02/using-ruby-on-rails-with-oracle-and-deploying-it-all-to-tomcat/

 

http://rubylearning.com/satishtalim/including_other_files_in_ruby.html#一个require和load的解释

 

====本文结束==== ----EOF---- 。。。。END。。。。

 

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