The reasons of making object extends its companion class?

[Shark.Z]

When using Lift Mappers, it's common to see code like this

object Post extends Post with LongKeyedMetaMapper[Post]

And there're several places in Lift API, I can see object extends its companion class.

object BindHelpers extends BindHelpers{ }

What's the meaning of this kind of usage?

[David Pollak]

On Mon, Feb 14, 2011 at 6:01 AM, Shark.Z <evo...@gmail.com> wrote:

When using Lift Mappers, it's common to see code like this

object Post extends Post with LongKeyedMetaMapper[Post]

So the MetaMapper can get the fields in the Mapper.
 

And there're several places in Lift API, I can see object extends its companion class.

object BindHelpers extends BindHelpers{ }

So that there's a trait available with various methods that you can mix into your classes.

The design of the traits that compose into Helpers is probably the biggest mistake in Lift.  It should have been all one big singleton.  Maintaining the separate traits is a real bear.  Finding the methods you want in traits scattered all over the place is a real bear.  People mix the various traits into classes and then have implicit mismatches (although this is less common in Scala 2.8).
 

What's the meaning of this kind of usage?

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