domenic at domenicdenicola.com (2013-11-03T22:03:43.418Z)
On Tue, Oct 29, 2013 at 10:04 AM, Brendan Eich <brendan at mozilla.com> wrote: > You bet, but special forms exist to have primitive semantics, which can be > meta-programmed only in certain ways (we try to preserve certain > invariants). With .equals, anything goes. With == where both operands are > object references, there has been an invariant. Allowing operator > customization to break that invariant might be worth the downside, but it > deserves discussion. Got it, worthy of discussion. My user data point is that I've never assumed == has that invariant. Overloading equals is a bigger deal, but it's not clear users should expect invariance given existing toString/valueOf issues. So +1 for this not being a blocker to extending your operator proposal more broadly.
On Tue, Oct 29, 2013 at 10:04 AM, Brendan Eich <brendan at mozilla.com> wrote: > Tristan Zajonc wrote: > >> >> if (mutMatA == mutMatB) { >> accidentallyMutate(mutMatA); >> assumeStillEqual(mutMatA, mutMatB, data); >> } >> >> >> Is this bug related to operator overloading? It seems just the nature of >> the beast with mutable reference types. Pretty much all JS matrix libraries >> today use: >> >> if (mutMatA.equals(mutMatB)) { >> accidentallyMutate(mutMatA); >> assumeStillEqual(mutMatA, mutMatB, data); >> } >> >> which I assume would suffer from the same bug? >> > > You bet, but special forms exist to have primitive semantics, which can be > meta-programmed only in certain ways (we try to preserve certain > invariants). With .equals, anything goes. With == where both operands are > object references, there has been an invariant. Allowing operator > customization to break that invariant might be worth the downside, but it > deserves discussion. > > Got it, worthy of discussion. My user data point is that I've never assumed == has that invariant. Overloading equals is a bigger deal, but it's not clear users should expect invariance given existing toString/valueOf issues. So +1 for this not being a blocker to extending your operator proposal more broadly. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20131029/3470e845/attachment-0001.html>