Using agents as an abstraction around states

The Agent module provides a basic server implementation and is a convenient way to spawn a process that needs to maintain a state. Agents in Elixir provide an intuitive API to update and retrieve the state.

In this recipe, we will create a module, phone_book.ex, where we will be able to store and retrieve data.

How to do it…

To create our phone book using an agent to maintain states, follow these steps:

1. Open your code editor and create a file named phone_book.ex.

2. Add the following code to the file you created:

   defmodule PhoneBook do
   
     @name __MODULE__
   
     def start_link do
       Agent.start_link(fn -> %{} end, name: @name)
     end
   
     def insert(user, number) do
       Agent.update(@name, &Map.put(&1, user, number))
     end
   
     def get(user) do
       Agent.get(@name, &Map.get(&1, user))
     end
   
   end

3. Start IEx and load the module:

   > iex phone_book.ex
   

4. Start the process that will hold our phone book data:

   iex(1)> PhoneBook.start_link
   {:ok, #PID...