Make the Iterator API public

[Diegovsky]

I'm writing code where Rhai can produce an iterable value such as an Array or a Range. It would be nice to be able to do value.iter() or something similar like the for x in value expression allows for. The page about iterators only mentions you can register custom ones, but not how to use them,

On a similar note, it would be cool for Rhai to have some sort of Iterator type, which is just a Box<dyn Iterator<Item=Dynamic>>, instead of eagerly evaluating iterators into arrays.

Related: #130

[Diegovsky]

As a workaround, I registered a global module with the following contents:

fn array(arg) {
    let it = [];
    for x in arg {
        it.push(x);
    }
    return it;
}

That way, scripts and rust-side can do array(<value>) and consistently get an array from an iterator.

Though, a proper Iterator API is still needed.

[schungx]

On a similar note, it would be cool for Rhai to have some sort of Iterator type, which is just a Box<dyn Iterator<Item=Dynamic>>, instead of eagerly evaluating iterators into arrays.

That would actually be a great idea. What if you register Box<dyn IntoIterator<Item=Dynamic>> into Rhai as an interator type? I suppose it should work?

EDIT: I tried it, and so far it doesn't work. Bummer. The Box needs to implement Clone which requires the trait object to implement Clone, which is not a trivial matter.

[schungx]

That way, scripts and rust-side can do array(<value>) and consistently get an array from an iterator.

It is not necessary. Rhai doesn't use actual pull-based iterators. It is merely syntactic sugar. At each step an iterators chain, it builds an array for the next step. Therefore you already get an array out of them.

Iterators are used primarily in the for loop, in which you'd need to use push to build an array.