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
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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
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irb(main):001:0> require 'active_support'LoadError: no such file to load -- active_supportfrom (irb):1:in `require'from (irb):1
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基本知识：require的寻找方法
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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。
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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：
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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
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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)=> trueirb(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～
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查看源码
ruby的require源码，只是个stub：
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def require(string) #This is a stub, used for indexing end
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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
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rubygems重载了require这个最基本的方法：
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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).
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? ? 所以这里改变了加载的路径
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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。
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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/
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http://rubylearning.com/satishtalim/including_other_files_in_ruby.html#一个require和load的解释
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====本文结束==== ----EOF---- 。。。。END。。。。
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