From: Gary Wright <gwtmp01@...>
Date: 2010-09-08T03:35:05+09:00
Subject: Re: Dynamic variables in blocks vs constants


On Sep 7, 2010, at 1:26 PM, Krzysztof Loch wrote:

> Hi, I know that dynamic variables created in block it is not accessible
> from outside of that block but I noticed that dynamic constants can be
> accessed and I want to know why it is so.

Because constants are always defined in reference to a module and not
in reference to the execution stack/context:

$ irb
ruby-1.9.2-p0 > module MyLibrary
ruby-1.9.2-p0 ?>  MyConstant = 3
ruby-1.9.2-p0 ?>  1.times {
ruby-1.9.2-p0 >     MyOtherConstant = 4
ruby-1.9.2-p0 ?>  }
ruby-1.9.2-p0 ?> end
 => 1 
ruby-1.9.2-p0 > 
ruby-1.9.2-p0 >   p MyLibrary.constants
[:MyConstant, :MyOtherConstant]
 => [:MyConstant, :MyOtherConstant] 
ruby-1.9.2-p0 > 

If there is no explicit module in scope then Ruby tucks constants
away in the class Object (classes are also modules in Ruby's object model)

$ irb
ruby-1.9.2-p0 > Object::Foo
NameError: uninitialized constant Foo
	from (irb):1
	from irb:17:in `<main>'
ruby-1.9.2-p0 > Foo = 3
 => 3 
ruby-1.9.2-p0 > Object::Foo
 => 3 
ruby-1.9.2-p0 > 

Constants defined in Object are also accessible via at Ruby's top level scope:

ruby-1.9.2-p0 > Object::PI = 3.1415927
 => 3.1415927 
ruby-1.9.2-p0 > PI
 => 3.1415927 
ruby-1.9.2-p0 > 



Gary