From: Ken Bloom <kbloom@...>
Date: 2009-03-16T01:07:41+09:00
Subject: Re: Basics of Require

On Sun, 15 Mar 2009 09:10:39 -0500, Mike Stephens wrote:

> I don't have access to an instance of Ruby at the moment and I am not
> clear what is being said in The Ruby Programming Language (Flanagan &
> Matsumoto). It says require code is executed immediately. It also says
> you can't insert the require code in the middle of something as if you
> are copy-and-pasting, so can you explain some basics of what actually
> happens?
 
> What are the differences between wrapping require code in 'Module',
> 'Def' and 'Class'?

def method
  require 'foo'
end

only loads 'foo' when you call the method. The contents of 'foo' are 
visible globally. (Unlike a #include in C)

module Foo
  require 'foo'
end

class Foo
  require 'foo'
end

These are exactly the same. They both load 'foo', and the contents of 
'foo' are NOT wrapped in the module or class Foo.

> The final question is in typical web environments like webrick, apache
> or eruby, does the require code get loaded and 'compiled' everytime any
> program refers to it or is there some mechanism to cache common code in
> 'compiled' form?

That depends on the environment. Webrick, which is a web server written 
in Ruby, keeps the same ruby interpreter running the whole time your 
server is running, so if you 'require' once, then the code stays loaded 
the whole time the server is running. With apache, it would depend on how 
you've set up apache to run the ruby interpreter. Eruby is a library that 
runs within a ruby interpreter, so it's not really relevant to this 
question.



-- 
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/