Designing Elixir Systems With OTP

Maps and Structs

The map has rapidly become the go-to data structure for Elixir programmers. For the purposes of this section, we’re going to treat maps and structs as basically the same thing. In IEx, you can see that a struct is actually implemented as a map. Let’s take a peek under the hood:

iex(1)> defmodule User do
...(1)>   defstruct [:name, :email]
...(1)> end
{:module, User, ...}
iex(2)> map = %User{}
%User{email: nil, name: nil}
iex(3)> is_map(map)
true
iex(4)> map.__struct__
User

So a User is actually a map. All structs have a __struct__ field that plain Elixir maps don’t have. Let’s look at the functions User supports. In IEx, type “User.” and then type tab, twice:

iex(5)> User.__struct__
__struct__/0 ...