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Base

A base is similar to a component except for two things:

It doesn’t have an interface.
It exposes a public API to the outside world.

The lack of an interface makes bases less composable than components. This is fine; the sole purpose of a base is to act as a bridge between the real world and the components it delegates to (via the components' interfaces). This structure gives us the modularity we need to build simple, understandable services and tools.

Let’s continue with our tutorial. The last thing you did was create a component. Run the following create base command to create a cli base:

poly create base name:cli

Your workspace should now look like this:

example
├── bases
│   └── cli (1)
│       ├── deps.edn
│       ├── resources
│       │   └── cli
│       ├── src
│       │   └── se
│       │       └── example
│       │           └── cli
│       │               └── core.clj
│       └── test
│           └── se
│               └── example
│                   └── cli
│                       └── core_test.clj
├── components
│   └── user
│       ├── deps.edn
│       ├── resources
│       │   └── user
│       ├── src
│       │   └── se
│       │       └── example
│       │           └── user
│       │               ├── core.clj
│       │               └── interface.clj
│       └── test
│           └── se
│               └── example
│                   └── user
│                       └── interface_test.clj
├── deps.edn
├── development
│   └── src
│       └── dev
│           └── lisa.clj
├── logo.png
├── projects
├── readme.md
└── workspace.edn

1	new `cli` base

Edit your ./deps.edn to add your newly created base:

 :aliases  {:dev {:extra-paths ["development/src"]

                  :extra-deps {poly/user {:local/root "components/user"}
                               poly/cli  {:local/root "bases/cli"}  (1)

                               org.clojure/clojure {:mvn/version "1.11.1"}}}

            :test {:extra-paths ["components/user/test"
                                 "bases/cli/test"]} (2)

1	Add the `cli` base as a dependency
2	Add the `cli` base tests

Cursive users: refresh your IDE to pick up the updates.

Now, add some code to the base:

(ns se.example.cli.core
  (:require [se.example.user.interface :as user])
  (:gen-class)) (1)

(defn -main [& args] (2)
  (println (user/hello (first args)))
  (System/exit 0))

1	:gen-class tells the Clojure compiler to generate a Java class
2	which allows the JVM to invoke `-main` when the `cli` base is invoked from the command line

The poly tool generated a deps.edn file for the cli base:

{:paths ["src" "resources"]
 :deps {}
 :aliases {:test {:extra-paths ["test"]
                  :extra-deps {}}}}

This is identical to the deps.edn poly generated when you created the user component. It will soon be needed when we create a project.

You never add a dependency from a base deps.edn to a component. The poly tool will automatically wire the cli base to the user component via its interface after you’ve added them to your project. Bases, or bricks for that matter, are unaware of concrete components; they only talk to interfaces.

We are getting closer to building a deployable artifact, which will turn your code into something useable, a command-line tool. To get there, you must first create a project.

❮Interface Project❯

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