Frankie Bagnardi wrote:
First, you shouldn’t assume this would be based on the Symbol.iterator protocol.Would |Object.create(null, {[Symbol.iterator]: value: ...})| work as it does in for..of?
No, as with instanceof and @@hasInstance in general, you wouldn't get membership test for free.
But unlike instanceof, you wouldn't get common case behavior for free either, so that's the downside. You'd have to provide a value such as Array#includes for the property named by Symbol.hasElement (or whatever the best name analogous to @@hasInstance is).
It seems like the main problem would be infinite sequences. That means either infinite loops (ugh), or the language/user setting an arbitrary number of max values to check (ew).
Neither.
If I do have an arbitrary iterable, I need to easily create something I can pass to for..of with |if (x of fn(xs))| where fn is provided by ecmascript.
You'd need to implement a separate MOP hook, let's call it @@hasElement for now.
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