Summer Update

Hi there!

I'll be taking a month-long vacation starting this weekend (family road trip), and I wanted to drop a quick line before I head off, and give a status update on longevity.

First off, I made a video tutorial last week that's pretty nice. It's about 70 minutes, but it's probably a comfortable watch for most people at 1.5x speed.

I've been playing around with early steps in migrating to shapeless on a feature branch. The first bite I broke off for this is to rewrite my test data generation tools using Arbitrary from ScalaCheck. It's not finished yet, but I got through the most worrisome part, which was, how am I going to generate all the implicit stuff used by shapeless libraries? In this case, I need a bunch of implicits to generate an Arbitrary[P] using scalacheck-shapeless. The worrisome part is that I have to generate the class for a user-provided type P. This is problematic in general, because in order to get things like a Generic[P], you have to have the actual type P right there in your hands. Nothing else will do - not a TypeTag, nothing else along those lines. Thankfully, I already have macros that produce scaffolding around the type P, so I can generate the code to produce the Arbitrary[P], and it ends up getting inserted right there in the user code, where P is well known. I'm sure happy about that because it means the major worry I had about implementing things with shapeless is now solved.

So that's on a branch, and I put that aside because I decided I really need to start focusing in on providing users a schema migration tool. It's really the last "absolutely must have" feature for longevity, and while working on making longevity more functional is very enticing, I need to keep my priorities straight. The last two functionalization tasks - the ModelEv, PEv, and Key type classes, and the finally tagless, were both super important, but most importantly, user-facing changes. Most of the rest of the functionalization work I want to do is more internal, and shouldn't affect the user API too much. So I can definitely de-prioritize it. Only thing is, I want to support options in queries, and I've sort of been delaying that until after shapeless is in place. I could actually do it before then, but it just isn't the most efficient course, as I would have to rewrite most of it in shapeless.

So when I come back in September, I'll definitely be focusing on schema migration tool first. Once I have a rudimentary working tool out, I'll probably start splitting my time between that and migrating to shapeless.

Have a great August everybody!

Longevity Release 0.23 - Use Type Classes to Improve Type Safety of Persistent API

This longevity release has been a long time in the making. The main improvement here, and the one that has taken by far the most effort, is instituting the use of type classes to provide type safety for the persistence API. I've done a technical writeup on this work in my previous blog post. It's actually pretty interesting because I've never seen type classes quite this way before, so I think it's worth the read. The TLDR is that the repository API is now fully type safe, and the last instance of forcing users to inherit from a longevity trait has been removed.

Here are some of the other major improvements in this release:

An Interesting Use for Type Classes in Scala

This is a technical writeup of the major new feature in the longevity 0.23 release.

There are more than enough writeups on using type classes in Scala already. I normally wouldn't bother to write about it, but I will now, for three reasons. First, the usage of type classes in longevity seems unique to me; I haven't seen type classes used quite this way before. Second, I want to write this up as documentation for any future contributors to the longevity project. Third, I'd really like to get your feedback into what I've done here, and hear your advice about how I might further improve on things.