From: matt@... (matt neuburg)
Date: 2009-03-16T02:57:40+09:00
Subject: Re: Basics of Require

Mike Stephens <rubfor@recitel.net> wrote:

> Ken Bloom wrote:
> >
> > 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.
> 
> I can't see the logic there. You're saying if the require is inside a
> method, Ruby will not doing anything until your program calls that 
> method. However if the require is inside a class, Ruby will go and fetch
> the code before you ever refer to that class?

The thing to grok here that is a class or module definition is itself
executable code. That, after all, is how the class gets defined! When
you say:

class MyClass
end

you really are executing code in order to bring the class into existence
(the constant name is created, etc).

When you think about it this way, you realize, aha! That's how stuff
like attr works. A big hunk of the coolness of Ruby depends upon this
very fact.

class MyClass
  attr :howdy # executes right now!
end

Similarly if you say

class MyClass
  puts "howdy"
end

... then "howdy" is output as soon as this code is encountered. It is
executable code.

But a method definition just defines a method. So when you say:

class MyClass
  def howdy
    puts "howdy"
  end
end

then "howdy" is not output, because all you did was define a method -
you haven't called it yet. The "def" is executed right now (i.e. the
method is indeed brought into existence) but its *contents* are not
executed (though of course the interpreter is applied to them, to make
sense of them). m.

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