Thread by @redrapids

Struct wizards Activate!

#elixirnewbie

1. The shorthand sigil syntax is great for structs.

defmodule User do
destruct ~w[name email]a
end

The ~w is a sigil with an array of words; the trailing a makes these atoms; the [] instead of () is a valid use of delimiters.

2. Structs are maps, with one extra key:

u = %User{}
-> %User{email: nil, name: nil}
Map.keys u
-> [:__struct__, :email, :name]
u.__struct__
-> User

3. Structs don't implement any Map protocols:

u[:name]
-> ...User does not implement the Access behaviour
u |> Enum.map(f(x) -> x end)
-> ...protocol Enumerable not implemented for %User...

4. Create a new struct by piping with the __struct__ function:

def new(fields)
fields
|> User.__struct__
|> validate
|> ...
end
...
User.new(name: "BT", email: "[e-mail]")

5. Require struct fields with @enforce_keys. To require name:

...
@enforce_keys [:name]
destruct [:name, :email]
...