Carry

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:

defmoduleInstrumentdodefstruct[: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.

Credits

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

NOTE

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

Installation

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

defdepsdo[{: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.