Starting many keys

(ns darkleaf.di.tutorial.h-starting-many-keys-test
  (:require
   [darkleaf.di.core :as di]
   [clojure.test :as t]))

A single di/start can start several components at once — a webserver and a worker queue and a scheduler in production, or a few independent components a test wants to poke at. Rather than writing an explicit root component that pulls all of them in, hand di/start a vector or a map of keys directly. The returned root supports the matching kind of destructuring.

(def a :a)
(def b :b)

Vector — Indexed root

A vector of keys produces a root that implements clojure.lang.Indexed. Sequence destructuring works directly — use di/with-open (a drop-in replacement for clojure.core/with-open that supports destructuring):

(t/deftest indexed-test
  (di/with-open [[a b] (di/start [`a `b])]
    (t/is (= :a a))
    (t/is (= :b b))))

Map — ILookup root

A map of label → key produces a root that implements clojure.lang.ILookup. Associative destructuring works:

(t/deftest lookup-test
  (di/with-open [{:keys [a b]} (di/start {:a `a :b `b})]
    (t/is (= :a a))
    (t/is (= :b b))))

The next chapter shows how to wire components into plain data — reitit routes, scheduler tables — with di/template and di/ref.