defmap

Defmap is a utility which allows you to embed a map into a module for faster/easier lookups. A lot of times you may want to have lookup tables in your app. e.g. when you need to map error codes to messages. Using Defmap, you directly embed the lookup map/table into your module, this improves the performance and decreases the memory used.

Example Usage

Simple lookup which adds a HttpStatusMessages.get method

defmodule HttpStatusMessages do
  use Defmap, map: %{
                       400 => "Bad Request",
                       401 => "Unauthorized",
                       403 => "Forbidden",
                     }
end

IO.inspect HttpStatusMessages.get(401) # => {:ok, "Unauthorized"}
IO.inspect HttpStatusMessages.get(3)   # => :error

Lookup with custom function name

defmodule HttpStatusMessages do
  use Defmap, func_name: :get_message, map: %{
                       400 => "Bad Request",
                       401 => "Unauthorized",
                       403 => "Forbidden",
                     }
end

IO.inspect HttpStatusMessages.get_message(401) # => {:ok, "Unauthorized"}
IO.inspect HttpStatusMessages.get_message(3)   # => :error

Multiple lookups

defmodule HttpStatusMessages do
  use Defmap, func_name: :get_message, map: %{
                       400 => "Bad Request",
                       401 => "Unauthorized",
                       403 => "Forbidden",
                     }

  use Defmap, func_name: :get_detailed_info, map: %{
                       400 => "Bad Request, happens when your input is invalid",
                       401 => "Unauthorized, happens when you don't have enough privileges",
                     }
end

IO.inspect HttpStatusMessages.get_message(401) # => {:ok, "Unauthorized"}
IO.inspect HttpStatusMessages.get_message(3)   # => :error

IO.inspect HttpStatusMessages.get_detailed_info(401) # => {:ok,  "Bad Request, happens when your input is invalid"}
IO.inspect HttpStatusMessages.get_detailed_info(3)   # => :error

Use a CSV file to store the map and then embed it at compile time

Contents of ./http_statuses.csv

417, Expectation Failed
500, Internal Server Error
205, Reset Content
...

defmodule HttpStatuses do
    use Defmap, map: (File.stream!(Path.expand(Path.join(__DIR__, "./http_statuses.csv")))
                      |> CSV.decode
                      |> Enum.reject(& length(&1) != 2)
                      |> Enum.map(fn [k, v] -> {String.to_integer(k), String.strip(v)} end)
                      |> Enum.into(%{})),
  func_name: :get_status
end

IO.inspect HttpStatusMessages.get_status(401) # => {:ok, "Unauthorized"}
IO.inspect HttpStatusMessages.get_status(3)   # => :error

Installation

The package can be installed as:

1. Add defmap to your list of dependencies in mix.exs:

def deps do
  [{:defmap, "~> 0.1.0"}]
end

2. Ensure defmap is started before your application:

def application do
  [applications: [:defmap]]
end