[infinispan-dev] Fwd: Lambda Serialization

[William Burns]

Sent that message a bit too soon.  Fixed a typo and added 9.0 version for
stream methods.

---------- Forwarded message ---------
From: William Burns <mudokonman at gmail.com>
Date: Tue, Feb 9, 2016 at 3:21 PM
Subject: Re: Lambda Serialization
To: infinispan -Dev List <infinispan-dev at lists.jboss.org>


Also I should note that this is not binary compatible since map/filter and
other intermediate operations will need to return a CacheStream instead of
a Stream as they do currently.   This is to make sure the terminal operator
when invoked is done upon the CacheStream which defines the Serializable
interfaces.  Thus it would have to wait until Infinispan 9.0.

This however would be used with [1], which is targeted for 8.2, to allow
for much easier way to provide Callable/Runnable instances through lambdas
without having to do the ugly casting.

[1] https://issues.jboss.org/browse/ISPN-6074

On Tue, Feb 9, 2016 at 11:36 AM William Burns <mudokonman at gmail.com> wrote:

> I wanted to propose a pretty simple way of making the lambdas serializable
> by default that I stumbled upon while working on another issue.
>
> I noticed that in the method resolution of the compiler it does some nice
> things [1].  To be more specific when you have 2 methods with the same name
> but vary by argument types, it will attempt to pick the most "specific"
> one.  Specific in this case you can think of if I can cast one argument
> type to the other but it can't be cast to this type, then this one is most
> specific.
>
> Here is an example, given the following class
>
> interface SerializableFunction<T, R> extends Serializable, Function<T, R>
>
> The stream interface already defines:
>
>    Stream map(Function<? super T, ? extends R> mapper);
>
> But we could add this to the CacheStream interface
>
>   CacheStream map(SerializableFunction<? super T, ? extends R> mapper);
>
> In this case you have 2 different map methods accessible from your
> CacheStream instance.  When passing a lambda the Java compiler will
> automatically choose the most specific one (in this case the
> SerializableFunction one since Function can't be cast to
> SerializableFunction).  This will then make the lambda automatically
> Serializable.  In this way nothing special has to be done (ie. explicit
> cast) to make the instance Serializable.
>
> This allows anyone using our Cache interface to immediately get lambdas
> that are Serializable when using Streams.
>
> The main problem however would be ambiguity because the Serialization
> would only be applied assuming you are using a defined class of CacheStream
> etc.  Also this means there are 2 methods (but that seems fine to me), so
> it could cause a bit of confusion.  The non serialization method is still
> helpful if people want to their own Externalizer, since their
> implementation doesn't have to implement Serializable then.
>
> What do you guys think?  It seems like a decent compromise to me.
>
>  - Will
>
>
>
>
>
> [1]
> https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.12.2.5
>
>
>
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