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From "Kenneth Knowles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (BEAM-2980) BagState.isEmpty needs a tighter spec
Date Wed, 23 May 2018 20:33:00 GMT

    [ https://issues.apache.org/jira/browse/BEAM-2980?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16487985#comment-16487985
] 

Kenneth Knowles commented on BEAM-2980:
---------------------------------------

I can dig that perspective, too. The issue hitting users is probably that "current" isn't
as obvious to them.

Unfortunately I don't see a good transcript anywhere of the conversation between the options
of "XYZState is always a changing view of an underlying ref cell" versus having a future-like
API. It does see that the utility of readLater() is tied to a particular implementation strategy
wherein local changes are buffered separately from whatever is read because of the hint.

TBH I just think futures are simpler. But I see that you'd need to refactor bits of the API,
for prefetching hint methods to cause futures to be delivered elsewhere, versus imperative
readLater() calls in the prefetch methods.

> BagState.isEmpty needs a tighter spec
> -------------------------------------
>
>                 Key: BEAM-2980
>                 URL: https://issues.apache.org/jira/browse/BEAM-2980
>             Project: Beam
>          Issue Type: Bug
>          Components: beam-model
>            Reporter: Kenneth Knowles
>            Assignee: Daniel Mills
>            Priority: Major
>
> Consider the following:
> {code}
> BagState<X> myBag = // empty
> ReadableState<Boolean> isMyBagEmpty = myBag.isEmpty();
> myBag.add(bizzle);
> bool empty = isMyBagEmpty.read();
> {code}
> Should {{empty}} be true or false? We need a consistent answer, across all kinds of state,
when snapshots are required.



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