Carry is a super simple, dependency free package that transforms a map from this form:

%{"carillon" => "sound", "marimba" => "percussion"}

to the corresponding Elixir struct.

For example, given this struct:

  defmodule Instrument do
    defstruct [:carillon]
  end

by invoking the function with the expanded struct:

iex> Carry.on(%{"carillon" => "sound", "marimba" => "percussion"}, %Instrument{})
%Instrument{carillon: "sound"}

or with the atom representing the struct

iex> Carry.on(%{"carillon" => "sound", "marimba" => "percussion"}, Instrument)
%Instrument{carillon: "sound"}

or as a syntactic sugar functionality

iex> Carry.on(%Instrument{carillon: "sound"}, Instrument)
%Instrument{carillon: "sound"}

which will just call struct(module, Map.from_struct(struct)) under the hood

This is usually useful when having a decoded payload from json (a map) and we want to convert to an Elixir struct.

This implementation does not use String.to_atom/1 in order to not exhaust the BEAM atom table limits, since atoms are not garbage collected.

I was using exconstrutor, however I noticed that it seems to generate new atoms in some corner cases. See appcues/exconstructor#25 to get more context.

Thanks to to the https://hex.pm/packages/poison library for heavy influence =)

If you are using Poison, you can just do Poison.decode(json_string, as: %YourStruct{})

If available in Hex, the package can be installed by adding carry to your list of dependencies in mix.exs:

def deps do
  [
    {:carry, "~> 0.1"}
  ]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/carry.