Ah. Crossed in the mail. Yes, Alan raises the same issues regarding the TDZ vs non-writable worry.
Thanks for the pointer. On Wed, Oct 24, 2018 at 11:01 AM Logan Smyth <[email protected]> wrote: > Here's one other post about this from Allen: > https://github.com/tc39/ecma262/issues/749#issuecomment-265637923 > > On Wed, Oct 24, 2018 at 10:42 AM T.J. Crowder < > [email protected]> wrote: > >> I'm curious if I've inferred the rationale for something correctly. >> >> The module namespace object properties for exports have `writable: true` >> in their property descriptors, but of course, they aren't writable (the >> module namespace object has its own [[Set]] implementation that returns >> false). I wondered why they weren't `writable: false`, so I went looking. >> >> I found discussion in the March 24 2015 meeting notes about whether to >> even have `getOwnPropertyDescriptor` work. The consensus was yes, it should >> work (mixins!), and that it should report a basic data property that isn't >> configurable -- but is writable. Yahuda Katz points out that: >> >> > it is writable, but it's not writable by you >> >> though that's not always true (it may be declared `const`; that >> information isn't leaked from the module, though). >> >> In the May 25 2017 notes I found a comment from Mark S. Miller in >> relation to `writable: true`: >> >> > Non-writeable provides guarantee. Writable provides no guarantee. >> >> And this exchange between Yahuda Katz, Allen Wirfs-Brock, and Adam Klein: >> >> > YK: There is a a new property that we define as writable that is not >> writable. >> > >> > AWB: Not new. >> > >> > AK: Since... Proxys! >> >> There was some discussion of considering some flag basically saying what >> YK said, e.g., it's writable, but not by you :-) -- but that was more a >> brief digression that didn't go anywhere. >> >> So, then, what I infer is: They're marked writable because: >> >> 1. They may be writable by the exporting module, so code can't assume the >> value won't change; `writable: false` would make that assumption valid >> 2. Whether or not they're writable by the exporting module isn't >> information that should leak out of it >> 3. Non-writable `writable: true` data properties were already a thing >> (Proxies) >> >> So the most sensible thing was `writable: true` rather than `writable: >> false`. >> >> How'd I do? :-) >> >> -- T.J. Crowder >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > -- Cheers, --MarkM
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