From: Robert Klemme <bob.news@...>
Date: 2006-01-11T00:58:02+09:00
Subject: Re: Use of eval

Rich wrote:
> I was thinking of adding a simple command console to a Ruby project
> I'm working on (something like a domain-specific REPL).  Under what
> execution environment do the "eval"-ed strings execute, relative to
> the execution environment that is calling the eval method?

Normally the binding of the caller is used but you can also provide a
binding explicitely:

class Test1
  def test1(b)
    eval("@foo = 123", b)
  end
  def test2()
    eval("@bar = 123")
  end
end
class Test2
  def test1()
    t = Test1.new
    t.test1(binding)
    [self, t]
  end
  def test2()
    t = Test1.new
    t.test2()
    [self, t]
  end
end


>> Test2.new.test1
=> [#<Test2:0x1019a748 @foo=123>, #<Test1:0x1019a718>]
>> Test2.new.test2
=> [#<Test2:0x10198c18>, #<Test1:0x10198be8 @bar=123>]

>  Can
> classes be opened using eval?

Strings must be syntactic correct Ruby.  You can of course add methods to
classes etc.

>  Finally, is there anything like Perl's
> Safe module available in Ruby?  Thank you.

Yes.  There is the thread global variable $SAFE which controls what can be
done.

Kind regards

    robert