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Re: Opacity considered harmful

This page is part of the web mail archives of SRFI 76 from before July 7th, 2015. The new archives for SRFI 76 contain all messages, not just those from before July 7th, 2015.

Tony Garnock-Jones wrote:
> Michael Sperber wrote:
>> Without opacity and with reflection, a client who
gets its hands on a
>> record can get at its fields, thus breaking the
abstractions provided
>> by the maker of that record.
> I see this as an unqualified benefit. [...]
> Sealedness and opacity have given me nothing but
trouble, and have on
> occasion cost my clients real money.

This sort of dilemma usually tells me that one should
think of
other alternatives. So how about this one?:

Provide opaque records but also provide clients with a
mechanism to get to the internal structure by force.
Ideally, the mechanism is highly visible
(syntactically), and too inconvenient to use 'by

A minimal design for this proposal is adding

So the final choice is with the client: Respect
opacity, or ignore it.

(The only compelling reason I see to have the final
choice with
the designer of the record type is security, and I
agree with
Mike that SRFI 76 is not the beast to send into that