[hibernate-dev] Returning Iterable

Emmanuel Bernard emmanuel at hibernate.org
Fri Mar 6 05:45:18 EST 2015

I heard it the first time, no need to draw guns :)
I just added another viewpoint as I happened to also ponder Iterable vs dedicated API on another pull request. 

> On 6 mars 2015, at 11:01, Sanne Grinovero <sanne at hibernate.org> wrote:
> I was already aware of that blog, and while he makes some interesting
> observations, I strongly disagree on it being a general rule. Like
> many of the people commenting on the blog post, and the author himself
> admits the title was too broad ;-)
> First of, it's an SPI that we consume ourselves. We *know* that all we
> need is to iterate, and the "for each" idiom is all we need.
> Exposing a List in this case was an error, as it's a leaky
> abstraction: there is no ordering requirement, and in fact I was
> hoping to replace the implementation with a Set but I couldn't do that
> as we committed to a contract which exposes a List.
> We all know the rules of encapsulation: expose the least possible, but
> no less... obviously the blog poster has a point in his case as he was
> bitten by the "no less" problem.
> I guess we all like encapsulation of classes, or we could as well move
> back to public static fields rather than accessors. And you all return
> "Set", and not "HashSet" right? Even though I often prefer to keep the
> private field to use the type of the concrete collection, as
> *privately* it may be useful (that's a case by case call).
> You expose the highest abstraction which satisfies the need, aiming at
> a good balance of practicality for both the implementor of the
> contract and the consumer.
> There also is a performance aspect. By returning List or Set, decency
> rules require me to wrap them in their immutable counterparts, or make
> defensive copies.
> But then when the collections' whole point is to actually mutate,
> you'd need to do such a wrap (or such a copy) on a per-invocation of
> the read.. even if you don't agree on it being a good enough
> performance reason, it adds on the readability of the code.
> Often that's not a big deal, still why do I need to pay for any cost
> if its reason to be is completely moot.
> Many of our internal contracts should be Iterable, especially if it's
> only about iterating _some collection_.
> It's different of course if you expose it as a domain model to a user
> API: in that case you don't really know what the use case's practical
> needs are going to need, and then like the blog states being able to
> run "size()" is often too compelling.
>> On 6 March 2015 at 08:12, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>> We had that debate in one of the PR. We ended up not returning it for other reasons.
>> A small additional stone to the discussion is here http://alexruiz.developerblogs.com/?p=2519
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