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It bears mentioning, by the way, that this is largely just a neat exhibition of some of Ruby's metaprogramming magic. The with statement itself isn't *that* useful, I think, and this implementation in particular is probably slow enough to not merit the tradeoff. But the implementation is (IMO) kinda neat :-)

Personally, I think he should have stuck with the instance_eval implementation. After all, Ruby is all about trusting programmers to follow the rules (typing, method checking etc...) and the result has been some impressively dynamic algorithms. Why not just carry that to the next level and trust developers to respect encapsulation? After all, if it's not in the public API and you're using it, it's your own fault if something goes wrong. :-)

Yes, but sticking with instance_eval is kind of useless. After all, if you're going to use instance_eval, use instance_eval :-) with is supposed to operate differently -- in a more limited way, encapsulation-wise, and a broader way, in terms of the access to the original binding scope.