[resending to all, in case Dave isn't subscribed to es-discuss]
On Tue, Jan 20, 2015 at 3:20 PM, David Ungar <[email protected]> wrote: > Funny you should send this to me now; I’ve been thinking it was time to > look up and chat with those of you whom I know. > > But on topic, the question in my mind would be: “Why does your language > support === in the first place?” > > In the Self/Smalltalk world, if A === B (it was called == in those > languages), it meant that no base-level message you could send would have > an observable difference > between sending to A vs B. > For instance the code (in JS syntax) > > setA.add(“foo”) > setA.print() > > would be the same as > > setB.add(“foo”) > setA.print // notice the setA > > iff it were true that setA === setB > > In order to support proxies, the language needs to allow for the > overriding of ===, and Self did exactly that. > > But it depends on the context, of course. > > - David > > > > On Jan 20, 2015, at 3:01 PM, Mark S. Miller <[email protected]> wrote: > > [+ungar, +tvcutsem] > > > On Tue, Jan 20, 2015 at 2:36 PM, Brendan Eich <[email protected]> wrote: > >> Mark S. Miller wrote: >> >>> >>> IIRC David Ungar's question to Tom was "why not enable proxies to >>> mega-program every base-level operation in the language?" I took >>> this to mean nothing like a nominal type check could evade >>> proxying, in David's vision. Is this plausible in your view? >>> >>> >>> No it is not. It destroys the whole point of branding if passing a brand >>> check guarantees nothing. >>> >> >> The counter-argument I inferred from the Q&A (this was in 2011, IIRC you >> were there too ;-) > > > > I was not there, but I talked to Tom soon afterward. CC'ing Dave and Tom, > who's memory of their conversation may also be informative ;) > > > >> would answer in two parts: >> >> 1. Needless-nominal type tests should be replaced by structural-type >> tests. >> >> 2. Any remaining brand or trademark test can use object identity or >> equivalent unforgeable capability. >> >> (2) can't be meta-programmed to spoof identity. But it doesn't leave >> anything like nominal types as found in many languages lying around as an >> attractive nuisance (and how, in Java!). >> > > What I think I remember hearing from Tom is that Dave's main point, and > the main argument with Tom, was precisely allowing proxies to intercede on > === checks, in which case you wouldn't even have that as a reliable > indicator. > > > >> >> Now plausible? > > > No. > > >> >> >> /be >> > > > > -- > Cheers, > --MarkM > > > -- Cheers, --MarkM
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