isabella232 / modular.co-dependency

Co-dependency support for com.stuartsierra.component

juxt.modular/co-dependency

Releases and Dependency Information

[juxt.modular/co-dependency "0.2.0"]

Usage

Add co-dependency to your project dependencies

(defproject your-project "your-version"
   ...
   :dependencies [[juxt.modular/co-dependency "0.2.0"]]
   ...
   )

Add component and co-dependency to your ns:

(ns your-app-ns
  (:require [com.stuartsierra.component :refer (using)]
            [modular.component.co-dependency :refer (co-using)]))

Define your system

Same as you do with stuartsierra/component lib but adding co-dependencies with co-dependency/co-using fn In this case :b depends on :a and :a co-depends on :b

(defn system-1 []
  (map->System1 {:a (-> (component-a)
                        (co-using [:b]))
                 :b (-> (component-b)
                        (using [:a]))
                 :c (-> (component-c)
                        (using [:a :b]))
                 :d (-> (component-d)
                        (using {:b :b :c :c}))
                 :e (component-e)})

Start your system

(def system-started-with-co-deps (co-dependency/start-system (system-1)))

Retrieving co-dependencies values

(def a (-> system-started-with-co-deps :a))
(def a-from-b (:a @(-> system-started-with-co-deps :a :b)))
;; checking identity equality
(assert (= a a-from-b))

Using stuartsierra reloaded workflow

If you use stuartsierra "reloaded" workflow then update original stuartsierra dev/start function by:

(defn start
  "Starts the current development system."
  []
  (alter-var-root #'system co-dependency/start-system))

Do you need more help?

Follow the test provided to learn how to use it :)

Drawbacks

In contrast with normal dependencies that you get using clojure map functions

(:dependency-key component)
;;=> dependency

when you want to retrieve a co-dependency you need to deref the co-dependency value

@(:co-dependency-key component)
;;=> co-dependency

Co-dependencies are NOT bound during a component's start phase.

Co-dependencies are bound after a component's start phase. Therefore, a component's co-dependencies will not be accessible, even via a dereference of the co-dependency, during a component's start.

Re-read that last paragraph until you understand that you cannot make use of a co-dependency's data until after the start phase of a given component. You can make use of a co-dependency's data after the component has been fully started, which usually means in a function (such as a Ring handler).

The penalty for not understanding this point is days spent figuring out why you can't see a co-dependency's data. It's because you're still trying to access this data within the start phase of your component. Don't do this. Defer the lookup until after the entire start phase of your system has completed.

License

Copyright © 2014 Juan Antonio Ruz (juxt.pro)

Distributed under the Eclipse Public License, the same as Clojure