Use JsValue for webidl sequence.

[derekdreery]

No description provided.

[alexcrichton]

Thanks for this! I'm not sure though if js_sys::Array is the right binding here, it looks like according to WebIDL it may suffice to take/return iterators as well? (I'm not super familiar with many of these APIs that take a sequence)

Do you know if other non-array types are accepted/returned?

[derekdreery]

I wasn't sure exactly what the semantics are. It sounds like sequences should be valid, but all the examples use Arrays. Maybe some experimentation is required.

[alexcrichton]

Ah yeah it's probably worth playing around with this a bit and some of the newly exposed API. One option is to just bind this as JsValue and let users interpret it though

[derekdreery]

I've done some experimentation on browsers in #1038

[derekdreery]

I've just set it to use JsValue for now.

[alexcrichton]

Ok looks good to me! Want to add a small test as well exercising this?

Also mind taking a look @fitzgen as well and confirming you're good w/ this strategy?

[fitzgen]

Is there a reason not to use js_sys::Iterator instead of JsValue?

https://docs.rs/js-sys/0.3.8/js_sys/struct.Iterator.html

[alexcrichton]

@fitzgen I think an Array couldn't be passed in because it's not a superclass, right?

[fitzgen]

@fitzgen I think an Array couldn't be passed in because it's not a superclass, right?

I'm not suggesting Array, only js_sys::Iterator which is a duck-typed thing for any JS object that implements the iterator protocol.

Maybe we are talking past each other here?

[alexcrichton]

@fitzgen oh sorry what I mean is that if we have fn foo(x: &js_sys::Iterator) then you can't easily-ish pass in &js_sys::Array

[fitzgen]

Is this issue specifically for parameters?

I would expect js_sys::Iterator for iterable return values, and I guess &JsValue for parameters.

[Pauan]

@alexcrichton Can't you just use foo(&x.values())? And we can provide a similar method on other iterable types. Maybe even backed by a trait.

[alexcrichton]

@fitzgen ah yeah sorry I'm thinking about parameters, but I think we still need Array on return types as well because there's not a next method on the Array types in JS, right? Ideally we'd return like a IntoIterator of some form I think?

@Pauan it's true yeah .values() would work! I think we ideally, though, want to expose the capabilities of web engines which is to accept both iterators and arrays so conversions that aren't necessary don't pull in overhead by accident.

[fitzgen]

@fitzgen ah yeah sorry I'm thinking about parameters, but I think we still need Array on return types as well because there's not a next method on the Array types in JS, right? Ideally we'd return like a IntoIterator of some form I think?

D'oh. yeah. I don't think we can rely on sequences being arrays though. I guess the most correct thing would be something like -> impl IntoIterator<Item = JsValue> or something like that...

Edit: See comment below

[fitzgen]

https://heycam.github.io/webidl/#es-sequence

IDL sequence values are represented by ECMAScript Array values.

[fitzgen]

That is pretty definitive. Ignore my comment about "I don't think we can rely on..."

[alexcrichton]

Ok I think we're probably good to go in this case with argument position as JsValue and return position as js_sys::Array. @derekdreery want to update the PR to return Array and it should be good to go then!

[derekdreery]

Ok sounds good!

[derekdreery]

Done. Also rebased and squashed.