Adding stream operators to list flyweight

[jitsni]

Need streaming operators on list flyweight to filter and reduce. For e.g: To filter an item, one could use the following:

listFW.stream().filter(x -> x.id() == key).findFirst()

Otherwise, forEach() needs to be used and store the item in a temporary holder and it is not convenient.

[dpwspoon]

I couldn't find a way to return a stream without creating a backing of the individual instances. I tried the following ways of generating the stream

1. static <T> Stream<T> iterate(T seed, UnaryOperator<T> f) and
2. static <T> Stream<T> generate(Supplier<T> s)

Perhaps we could add the Stream methods directly to the flyweight (like rename the flyweight StreamFlyweight).

Otherwise we could look at stream support

[dpwspoon]

What about adding:

public boolean anyMatch(Predicate<T> filter) {
    for (int offset = offset(); offset < maxLimit(); offset = itemRO.limit()) {
        itemRO.wrap(buffer(), offset, maxLimit());
        if (filter.test(itemRO)) {
            return true;
        }
    }
    return false;
}

[dpwspoon]

Added anyMatch here: #22. This or related functionality is very useful as doing it in downstream code via forEach requires effectively final variable to be set (aka, need a reference to containing object field).

[jitsni]

anyMatch would be good addition as I am running into the same. For e.g: I want to check if there is any error in one of the items in the list. I am doing this now:

        boolean[] errors = new boolean[1];
        listFW.forEach(h -> errors[0] = errors[0] || h.error());

Stream has the same method, but signature is slightly different.

    boolean anyMatch(Predicate<? super T> predicate);

can you update the signature in the PR ?

[dpwspoon]

The PR currently generates

public boolean anyMatch(Predicate<T> predicate)

Are you saying it should be Predicate<? super T> predicate ?

or Predicate<T> predicate ?

I’m not sure which is correct but Predicate<T> predicate matches the current implementation of forEach

[jitsni]

I think it should be Predicate<? super T> which is more allowing. For eg if I have ListFW<Http2DataFrame> then I can use Predicate<Http2Frame>. I think even forEach also. But right now, I am not running into this (though I have inheritance relations among the HTTP2 frame types)

[dpwspoon]

Ok, I'll change both on the PR. Also, I would like to remove the quotes on the toString as I just spent quite some time debugging an issue where I did toString() instead of asString()... thoughts?

[dpwspoon]

I hit the above today and needed the <? super T> for the forEach :-). PR is updated

[cmebarrow]

@jitsni Can we close this given that PR #22 (for anyMatch) has been merged?

[dpwspoon]

Reopening, I would still like this or something equivalent. Because stream().filter() requires intermediate objects (I believe), perhaps we could implement:

matchFirst(x -> x.id() == key) or firstMatch(x -> x.id() == key)