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.
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
endIn 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"
endIn order to get proper formatting, you should add the following option to your .formatter.exs
locals_without_parens: [defdelegate: 1]
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"}
]
endDocumentation can be found at https://hexdocs.pm/protoss.