From: Phrogz <gavin@...>
Date: 2006-02-27T02:23:34+09:00
Subject: Scope of constants in instance_eval

I'm writing a DSL, and I want to use some constants. To be clean, I
don't want to pollute the global constant space. To be tight, I also
don't want the user to have to scope the constant using Foo::BAR, but
instead be able to use just BAR.

The following surprised me. As the scope of the block is an instance of
Foo, I had hoped/assumed that it would have access too Foo's constants.
Alas, no.

class Foo
  BAR = 1
  def initialize( &block )
    instance_eval &block
  end
  def bork
    puts "bork: self is #{self}"
    puts "bork: BAR is #{BAR}!"
  end
end

Foo.new{
  bork
  puts "block: self is #{self}"
  puts "block: BAR is #{BAR}!"
}

#=> bork: self is #<Foo:0x32c808>
#=> bork: BAR is 1!
#=> block: self is #<Foo:0x32c808>
#=> NameError: uninitialized constant BAR


For now, I'll just shove my constants into global space before the
instance_eval, and remove them afterwards. Is there a better/cleaner
way to accomplish my goals?