From: Robert Klemme <bob.news@...>
Date: 2005-03-31T16:39:44+09:00
Subject: Re: changing the context in which a block executes


"John-Mason P. Shackelford" <john-mason@shackelford.org> schrieb im
Newsbeitrag news:424B14FE.3020000@shackelford.org...
> Greetings.
>
> I'd like to define a method which accepts a block such callers can
write:
>
> some_method do
>    op1(arg)
>    op2(arg)
> end
>
> instead of:
>
> some_method do |obj|
>    obj.op1(arg)
>    obj.op2(arg)
> end
>
> Since within a block self.class.name always returns Object (not the
> object of the method which takes the block) it is necessary to use
> instance_eval to expose methods available within the context of the
> block. This however, breaks encapsulation exposing an object's instance
> data and private methods to the block.

In Ruby you can *always* directly access an instance's state and thus
encapsulation is never really enforced:

>> class Foo
>> attr_accessor :bar
>> end
=> nil
>> f=Foo.new
=> #<Foo:0x101c8928>
>> f.bar = 10
=> 10
>> f.instance_variables
=> ["@bar"]
>> f.instance_variable_get "@bar"
=> 10

So strictly speaking, you cannont prevent someone from accessing instance
state.  There might be ways but they are usually far too complex to bother
to use them.

Kind regards

    robert