While static analysis is one advantage, there are additional reasons for
this to be a syntactic proposal. A helper method like `Map.fromObject`
could indeed be a useful addition to the language (though it is simple
enough to do already: `new Map(Object.entries(obj))`) — however that does
not work for maps whose keys are not also valid property keys.

In general I’m in the less-new-syntax camp, but I find this idea
intriguing. My initial impression is that it’s fairly convincing, mainly
because my (purely anecdotal) experience is that it is an attempt to solve
a real problem — many devs seem to be reluctant to use `Map` and `Set`,
despite knowing they exist and are sometimes more appropriate models, and I
think it is in part due to their "second class" nature; in ES folks are
accustomed to "seeing" data structures. Similarly there is reluctance to
work with subclasses of data structures, which are put on equal-footing by
this proposal.

The `#` is indeed ugly, but the particular symbol I imagine is highly
bikesheddable and consideration of it could probably be deferred till it’s
determined whether the core ideas of the proposal represent a worthwhile
addition.
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While static analysis is one advantage, there are additional reasons for
this to be a syntactic proposal. A helper method like `Map.fromObject`
could indeed be a useful addition to the language (though it is simple
enough to do already: `new Map(Object.entries(obj))`) — however that does
not work for maps whose keys are not also valid property keys.

In general I’m in the less-new-syntax camp, but I find this idea
intriguing. My initial impression is that it’s fairly convincing, mainly
because my (purely anecdotal) experience is that it is an attempt to solve
a real problem — many devs seem to be reluctant to use `Map` and `Set`,
despite knowing they exist and are sometimes more appropriate models, and I
think it is in part due to their "second class" nature; in ES folks are
accustomed to "seeing" data structures. Similarly there is reluctance to
work with subclasses of data structures, which are put on equal-footing by
this proposal.

The `#` is indeed ugly, but the particular symbol I imagine is highly
bikesheddable and consideration of it could probably be deferred till it’s
determined whether the core ideas of the proposal represent a worthwhile
addition. FWIW though, one alternative might be _no_ symbol; `Map {}` (with
a "No Line Terminator Here") is currently invalid syntax.