Yep.
Cheers,
Alan
>________________________________
>From: David Barbour <[email protected]>
>To: Fundamentals of New Computing <[email protected]>
>Sent: Wednesday, September 7, 2011 1:50 PM
>Subject: Re: [fonc] Tension between meta-object protocol and encapsulation
>
>
>On Wed, Sep 7, 2011 at 12:48 PM, Casey Ransberger <[email protected]>
>wrote:
>
>It seems to me that there is tension here, forces pulling in orthogonal
>directions. In systems which include a MOP, it seems as though encapsulation
>is sort of hosed at will. Certainly I'm not arguing against the MOP, it's one
>of the most powerful ideas in programming. For some things, it seems
>absolutely necessary, but then... there's the abuse of the MOP.
>>
>>
>>Is this tension irreconcilable?
>
>
>There are patterns for meta-object protocol that protect encapsulation (and
>security).
>
>
>Gilad Bracha discusses capability-secure reflection and MOP by use of
>'Mirrors' [1][2]. The basic idea with mirrors is that the authority to reflect
>on an object can be kept separate from the authority to otherwise interact
>with the object - access to the MOP is not universal.
>
>
>Maude's reflective towers [3] - which I feel are better described as 'towers
>of interpreters' - are also a secure basis. Any given interpreter is
>constrained to the parts of the model it is interpreting. By extending the
>interpreter model, developers are able to achieve ad-hoc extensions similar to
>a MOP.
>
>
>These two classes of mechanisms are actually quite orthogonal, and can be used
>together. For example, developers can provide frameworks or interpreters in a
>library, and each interpreter 'instance' can easily export a set of mirror
>capabilities (which may then be fed to the application as arguments).
>
>
>[1] Mirrors: Design Principles for Meta-level Facilities of Object-Oriented
>Programming Language. Gilad Bracha and David
>Ungar. http://bracha.org/mirrors.pdf
>[2] The Newspeak Programming
>Platform. http://bracha.org/newspeak.pdf (sections 3,4).
>[3] Maude Manual Chapter 11: Reflection, Metalevel Computation, and
>Strategies. http://maude.cs.uiuc.edu/maude2-manual/html/maude-manualch11.html
>
>
>We can use power responsibly. The trick is to control who holds it, so that
>power is isolated to the 'responsible' regions of code.
>
>
>Regards,
>
>
>Dave
>
>
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