Vavr: Add syntactic sugar for Iterator creation

[danieldietrich]

It would be great to have an additional factory method

interface Iterator<T> {

    static <T> Iterator<T> iterate(Supplier<Boolean> hasNext, Supplier<? extends T> next) {
        return new AbstractIterator<>() {
            @Override
            public boolean hasNext() {
                return hasNext.get();
            }
            @Override
            public T getNext() {
                return next.get();
            }
        };
    }

}

It makes sense to also add this method to Stream:

interface Stream<T> {

    static <T> Stream<T> iterate(Supplier<Boolean> hasNext, Supplier<? extends T> next) {
        return Stream.ofAll(Iterator.iterate(hasNext, next));
    }

}

Hint: The addition might introduce ambiguities regarding existing iterate() methods.

[nfekete]

Another factory method worth considering could be one accepting a Supplier<Option<? extends T>>,
which would repeatedly invoke the supplier while it's a Some and end on the first None.

[chb0github]

I like @nfekete idea because it allows the data and the predicate to be tied together.

[chb0github]

what about

interface Iterator<T> {

    static <T> Iterator<T> iterate(Supplier<? extends T> next, Predicate<? extends T> until);
}

so you can do Iterator.iterate(StringUtils::randomString,s -> s.length() > 10)

[valery1707]

@chb0github your Iterator#iterate(Supplier<T>, Predicate<T>) can be replaced with exists Iterator.continually(Supplier<T>).takeUntil(Predicate<T>): Iterator.continually(StringUtils::randomString).takeUntil(s -> s.length() > 10)

[valery1707]

Variant iterate(Supplier<Option<? extends T>>) is more suitable as I think.
This situation looks like the https://github.com/vavr-io/vavr/issues/2134#issuecomment-342297157

[ruslansennov]

iterate(Supplier<Boolean> hasNext, Supplier<? extends T> next) requires synchronized common state of both suppliers. In fact, one should implement Supplier<Option> factory and pass it to Iterator.iterate(Supplier, Supplier). I believe Iterator.iterate(Supplier<Option>) is enough.

[danieldietrich]

I believe Iterator.iterate(Supplier) is enough.

Yes, I also think @ruslansennov is right. Will close this ticket.

Solved with #2193