View Source Structs

A Struct is an extension of a Map and is defined inside a Module. It allows you to define fields at compile-time, require certain fields, set default values, and it raises if you try to set a field that doesn't exist. You can define a struct with defstruct/1.

defmodule RunElixir.Profile do
  # Make the :name field required
  @enforce_keys [:name]
  defstruct [:name, :age, status: :active] # <- Set the default value of :status to :active

  # You can match against the struct like this.
  # This function raises if it receives a plain map and not a struct.
  def adult?(%RunElixir.Profile{age: age}) do
    age >= 18
  end
end

You can create a struct like this:

struct = %RunElixir.Profile{name: "Peter", age: 21}

# You can access the struct's fields using the dot-notation
struct.name # => "Peter"
struct.status # => :active

Structs give you some nice checks for free, like an exception if you try to set a field that doesn't exist.

struct = %RunElixir.Profile{height: 190}

** (KeyError) key :height not found
    expanding struct: RunElixir.Profile.__struct__/1

Structs can also require fields and raise if they are not set.

struct = %RunElixir.Profile{age: 21}

** (ArgumentError) the following keys must also be given when building struct RunElixir.Profile: [:name]
    expanding struct: RunElixir.Profile.__struct__/1