A protocol for converting custom Elixir structs into a Msgpack-encodable format.

This protocol provides a hook into the Msgpack.encode/2 function, allowing developers to define custom serialization logic for their structs.

Contract

An implementation of encode/1 for a struct must return a basic Elixir term that the Msgpack library can encode directly. This includes:

• Maps (with string, integer, or atom keys that will be converted to strings)
• Lists
• Strings or Binaries
• Integers
• Floats
• Booleans
• nil

It is important that the returned term must not contain other custom structs that themselves require an Encodable implementation. The purpose of this protocol is to perform a single-level transformation from a custom struct into a directly encodable term. Returning a nested custom struct will result in an {:error, {:unsupported_type, term}} during encoding.

Example

defimpl Msgpack.Encodable, for: User do
  def encode(%User{id: id, name: name}) do
    # Transform the User struct into a map, which is directly encodable.
    {:ok, %{"id" => id, "name" => name}}
  end
end