The url shortener Elixir app

So far my Elixir journey has focused more on independent features of the language and less about real app construction. The next 15/20 days will be a bit different because I'm now ready to apply everything I've learned in hopes of going deeper. With each iteration I'll be adding something new or improving some functionality from a previous post.

The application itself will be simple and much less the focus of this series as you might imagine. The url shortener has a small api surface area and offers enough (primitive) "real world" requirements that it should make for a great learning playground.

Part 1: mix new

The first step is to run `mix new` from the command line. This will scaffold everything we need to kickstart a simple project in Elixir.

    mix new example
  

Before we dive into building the web interface or anything to make this concurrent I first wanted to write the most basic module required. Start by adding a module called `Shortener`. In this module we will first implement a function called `create_short_url` that is responsible for inserting the url and hash (alias). Next implement a function called `get_url` that is responsible for retrieving the url given some hash (alias).

    defmodule Shortener do
      def new(), do: %{}
    
      def create_short_url(state, hash, url) do
        Map.put(state, hash, url)
      end
    
      def get_url(state, hash) do
        Map.get(state, hash, :undefined)
      end
    end
  

To see this in action we next write a unit test to exercise the 2 functions together. You can run this from the command line using `mix test`.

    defmodule ShortenerTest do
      use ExUnit.Case, async: true
    
      setup do
        Shortener.new()
      end
    
      test "create will add key/value given url and hash", state do
        assert Shortener.get_url(state, "x") === :undefined
    
        new_state = Shortener.create_short_url(state, "x", "google.com")
    
        assert Shortener.get_url(new_state, "x") === "google.com"
      end
    end
  

Note: the state returned from `setup` is made available to each unit test as `state` just before the `do`

To play around with this module in IEx run this command `iex -S mix run`

    state = Shortener.new()
    new_state = Shortener.create_short_url(state, "x", "google.com")
    Shortener.get_url(new_state, "x")
  

You can track my progress on github commit by commit. If you just want the code for this post checkout this commit.