Create Component

Create a new Clojure component following project conventions. Before starting, read docs/clojure.org.

Component Structure

Every component namespace follows this structure:

(ns bits.foo
  (:require
   [bits.spec]
   [clojure.spec.alpha :as s]
   [com.stuartsierra.component :as component]))

;;; ----------------------------------------------------------------------------
;;; API

(defn do-thing
  [foo-component arg]
  ;; Component as first argument
  ...)

;;; ----------------------------------------------------------------------------
;;; Component

(defrecord Foo [config-val other-val]
  component/Lifecycle
  (start [this]
    ;; Initialize, return updated this
    this)
  (stop [this]
    ;; Cleanup, return this
    this))

(defn make-foo
  [config]
  {:pre [(s/valid? :bits.foo/config config)]}
  (map->Foo config))

(defmethod print-method Foo
  [foo ^java.io.Writer w]
  (.write w "#<Foo>"))

Specs in bits.spec

To avoid cyclic dependencies, put component config specs in bits.spec:

;; In bits.spec (use literal keywords)
(s/def :bits.foo/config-val string?)
(s/def :bits.foo/config
  (s/keys :req-un [:bits.foo/config-val]))

Configuration in bits.app

All defaults live in bits.app/read-config:

;; In bits.app
(defn read-config []
  {:foo {:config-val "default"}
   ...})

BANNED:

• Defaults in component namespace
• System/getenv outside bits.app
• Optional parameters on make-* functions

Wire into System

Add to bits.app/make-system:

(component/system-map
  ...
  :foo (component/using
         (foo/make-foo (:foo config))
         [:dependency-component]))

Checklist

1. Spec in bits.spec with literal keywords
2. Config defaults in bits.app/read-config
3. Record implements component/Lifecycle
4. Factory is make-<name> with :pre validation
5. Print method hides sensitive data
6. API functions take component as first arg
7. Wired into system with dependencies

$ARGUMENTS