On 2010-12-21 08:27, David-Sarah Hopwood wrote: > The private names and soft field proposals are similar in the > visibility mechanisms they can simulate, but soft fields are slightly > more general. In either proposal, visibility can be restricted to a > particular lexical scope. In the soft fields proposal, because > SoftFields are first-class values, it can also be restricted to any > set of objects that can get access to a given SoftField.
Correction: the #.id syntax also allows private names to be treated as first-class values, so the proposals are equivalent in this respect. > I don't > claim this to be a critical benefit, but it is occasionally > useful in object-capability programming. For example, in > <http://www.erights.org/elib/capability/ode/ode-capabilities.html#simple-money>, > a Purse of a given currency is supposed to be able to access a > private field of other Purses of the same currency, but not other > Purses of different currencies. The implementation at > <http://www.eros-os.org/pipermail/cap-talk/2007-June/007885.html> > uses WeakMaps to do this, and could just as well use soft fields or private names > if transliterated to ECMAScript. -- David-Sarah Hopwood ⚥ http://davidsarah.livejournal.com
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