Managing Clojure app state since (reset)

After shipping two large projects with component, and having several in works, I decided, Component is not for me, and wrote mount.

Here are the differences between mount and Component, and below is the story of why.

Java is Good


For the last several years Java started to get a bad rep by many people who now like “better” languages. Java is too verbose, too complex, too mutable, too ugly, too last century, etc..

I like Java, I liked it 10 years ago, I like it now. I did work in many languages, who doesn’t now days, and I still like Java. Java is solid. Java is simple. Yes, it is.

There are many corner cases that are well documented, and there are more that are not documented, but it does not make it complex. You can learn about Monads and Endofunctors on your own, while completing and shipping successful Java projects. Category Theory is not a prerequisite. Java is stable. I like Java.

Love is not solid, it’s more


Now I can’t say I love Java. Java is my good friend, we have a solid relationship. Sometimes we go to work together, but I do not have a feeling of excitement, I am not running (well, not too fast at least) to my laptop to try this cool Java thing, I would not spend a weekend with it unless we need to.

That’s where Clojure comes in. I love it. I won’t go into details on why I love it, first of all its personal, second of all there are plenty of other blog posts, books, videos that make Clojure shine. I just want to state that I love it. There is a difference.

Clojure. The Beginning.


I came to Clojure several years ago from a pretty common background: lots of Java and Spring. I like Spring a lot. It makes Java world shine, it taught me great ways to approach problems, it has great documentation and friendly community, I love friendly communities.

As I wrote more and more Clojure I fell in love with each new discovery, it made me think of time in a way Java didn’t. It greatly extended my reach into science behind a language.

Time went on and I started doing Clojure professionally. It is quite a different experience between using Clojure side by side with Java / Scala projects, using Clojure for tools and libraries, and using Clojure professionally: for products/applications. Products are very different and very stateful beings.

Clojure Developers are People


The question of state beyond a “map” or a “vector” in a lexical scope, but a product state, became the one of great importance. And the choices are not great here.

From talking to people I concluded that

* some people keep their product (application) states in “def”s
* some in “atoms”
* others in Component

The “Clojure Gods” talk a lot about state, but very rarely about an application state and codebase organization. I doubt Datomic uses Component, but I don’t know.

Since Component was gaining popularity, and I talked to JUXT people (great people btw), they seem to be very enthusiastic about it, I decided to give it a go.

Component Framework


When I started creating projects with Component, I already learned to like the Clojure way of functions and namespaces, so an object (record) oriented approach of Component was immediately suspicious.

Component is not exactly Spring of course. It aims to structure a stateful application, so it is reloadable in REPL, since REPL restart time is, well, slow.

In order to do that effectively, Component requires a whole app buy in, which makes it a framework rather than a library: another “unClojure” feeling that stayed with me while using Component.

Spring is a framework, and I like it. But in Java world that’s the culture. “Frameworks” is the approach. It is well accepted and tools are built around this.

Clojure world is all about libraries, and I love it, the same way I love open source solutions vs. closed packaged ones, i.e. open systems vs. closed systems. High cohesion, loose coupling, win win.

At Large


I understand that many people like Component, and I think their projects are based on it. Although it is not exactly evident, since most of products, Component would be needed for, are proprietary: enterprise (a.k.a. “at large”), “startups”, etc.. But there are several open source ones that look really good. A couple examples:

* Onyx
* BirdWatch

although BirdWatch switched from Component to system-toolbox:

“I have thrown out the Component library in master on GitHub, and I find using the systems-toolbox much more straight-forward”

I like Scotch


Long story short, while I delivered with Component, it did not deliver for me.

I rewrote Component projects with mount, and already shipped two of them. Both are live and blooming in prod.

Another team I work with liked this approach a lot, and rewrote one of their products in mount as well. First thing one of their developers said after trying it: “oh.. look, it’s like Clojure again!”.

It is, it is Clojure again for me too. I get it, Component may “do it” for many people, but alternatives are great!

I like Java, I love Clojure.