Understanding Join Internals

[Atri Sharma <at...@gmail.com>]

Hi All,


I needed some help in understanding join internals please. I
understood EnumerableJoin and its internals, but not sure as to how
the translation to EnumerableDefaults went through. Specifically, I
did not understand why EnumerableJoin does not have a physical
equivalent that implements EnumerableDefaults#join and why it goes
through to EnumerableDefaults. Is EnumerableDefaults is the physical
conversion operator for all Enumerable* logical operators?

Please advise.

Regards,

Atri

Re: Understanding Join Internals

[Julian Hyde <jh...@apache.org>]

Enumerable is a “wide” interface with a lot of methods, and I didn’t want every implementation to have to implement every method. So I created the class EnumerableDefaults to hold those default implementations. The methods are static but the first argument is always the Enumerable.

If we only supported JDK 8 and above I would have used the feature that allows default implementations of interface methods[1]. I was basing the linq4j API on LINQ[2] and lack of default methods was galling, because C# has had default methods for a long time.

Julian

[1] https://docs.oracle.com/javase/tutorial/java/IandI/defaultmethods.html <https://docs.oracle.com/javase/tutorial/java/IandI/defaultmethods.html>

[2] https://msdn.microsoft.com/en-us/library/system.linq.enumerable(v=vs.110).aspx <https://msdn.microsoft.com/en-us/library/system.linq.enumerable(v=vs.110).aspx> 

> On Jul 17, 2017, at 9:51 AM, Atri Sharma <at...@gmail.com> wrote:
> 
> Hi All,
> 
> 
> I needed some help in understanding join internals please. I
> understood EnumerableJoin and its internals, but not sure as to how
> the translation to EnumerableDefaults went through. Specifically, I
> did not understand why EnumerableJoin does not have a physical
> equivalent that implements EnumerableDefaults#join and why it goes
> through to EnumerableDefaults. Is EnumerableDefaults is the physical
> conversion operator for all Enumerable* logical operators?
> 
> Please advise.
> 
> Regards,
> 
> Atri