From: "Julian I. Kamil" <julian.kamil@...>
Date: 2006-03-18T07:43:48+09:00
Subject: Selective runtime provision of instance methods

I'd like to get some comments and suggestions from anyone who may have
an opinion on this or know of a better way to accomplish this.

I have an object with a lot of methods and variables some of which (but
not all) I'd like to make callable from another object that happens to
be evaluated by ERB.  So I did this:

<code>
class LotsOfMethods
    # to be made callable
    def method1 ... end
    def method2 ... end
    ...

    # not callable
    def methodX ... end

    def delegate
        d = OpenStruct.new({
            :var1 => var1,
            :var2 => var2,
            ...
            })

        my = self
        d_singleton = class << d; self end
        d_singleton.send(:define_method, :method1) { my.method1 }
        d_singleton.send(:define_method, :method2) { my.method2 }
        ...

        d
    end
end

class Sandbox
    def self.env(delegate)
        Proc.new {}
    end
end

sacred_object = LotsOfMethods.new
output = ERB.new(text).result(Sandbox.env(sacred_object.delegate))
</code>

The idea is that the embedded Ruby code in "text" will be able to
access the specified variables and methods in 'delegate' but not any
others.  So, for example:

text = '<%= delegate.method1 %>'

will be allowed; but:

text = '<%= delegate.methodX %>'

will raise an exception.

Does anyone know of a better way to accomplish the same effect?

Best regards,

Julian I. Kamil <julian.kamil@gmail.com>
http://pandora.rubyveil.com/ - Pandora Publisher
http://books.rubyveil.com/ - The Ruby Bookshelf