Protoss

Evil and Powerful Protocols for Elixir

Protocols are just modules! And sometimes you just want to do module things in protocols. And when you're in control of both the protocol and the module you're implementing for, colocating the code in the module you're writing just makes sense. This library does this automatically for you.

Usage

Protocol definition

use Protoss

defprotocol MyProtocol do
  # this works like a normal protocol forward definition.
  def fun_must_be_implemented(argument)

  # delegations forward to the passed module.  Currently
  # this is not currently runtime-checked, but it will be 
  # in the future under a flag.
  #
  # call as:
  # `MyProtocol.from_json(MyStruct, ...)`
  #
  defdelegate from_json(module, argument)

  # after block separates protocol code from module code
after

  # struct protocol implementations MUST implement these
  # extra callbacks:
  @callback extra_callback() :: term

  # this can be called directly as: `MyProtocol.root_function()`
  def root_function do
    :ok
  end
endcopy

Protocol implementation

In your (struct) protocols, the implementation of MyProtocol from above would look like this.

defmodule MyStruct do
  defstruct [:value]

  use MyProtocol

  @impl MyProtocol
  def fun_must_be_implemented(%__MODULE__{value: value}), do: value

  # note the arity change!
  @impl MyProtocol
  def from_json(%{"value" => value}), do: %__MODULE__{value: value}

  @impl MyProtocol
  def extra_callback, do: "I was required to implement this"
endcopy

Formatter changes

In order to get proper formatting, you should add the following option to your .formatter.exs

locals_without_parens: [defdelegate: 1]

Installation

The package is available on hex and can be installed by adding protoss to your list of dependencies in mix.exs:

def deps do
  [
    {:protoss, "~> 0.2"}
  ]
endcopy

Documentation can be found at https://hexdocs.pm/protoss.