A struct used to represent the MessagePack Extension type.

Examples

Let’s say we want to be able to serialize a custom type that consists of a byte data repeated reps times. We could represent this as a RepByte struct in Elixir:

defmodule RepByte do
  defstruct [:data, :reps]
end

A simple (albeit not space efficient) approach to encoding such data is simply a binary containing data for reps times: %RepByte{data: ?a, reps: 2} would be encoded as "aa".

We can now define the Msgpax.Packer protocol for the RepByte struct to tell Msgpax how to encode this struct (we’ll choose 10 as an arbitrary integer to identify the type of this extension).

defimpl Msgpax.Packer, for: RepByte do
  def transform(%RepByte{data: b, reps: reps}) do
    Msgpax.Ext.new(10, String.duplicate(<<b>>, reps))
    |> Msgpax.Packer.transform()
  end
end

Now, we can pack RepBytes:

iex> packed = Msgpax.pack!(%RepByte{data: ?a, reps: 3})
iex> Msgpax.unpack!(packed)
#Msgpax.Ext<10, "aaa">