BinStructCustomType is user defined type when you need most control of how data are parsed.

Such custom type can be used in place you would use BinStruct.

The only currently limitation it can't be used directly inside variant_of (variant_of dispatching relays on elixir struct).

Required functions to be defined by custom type:

• either parse_returning_options/3 or parse_exact_returning_options/3
• size/2
• known_total_size_bytes/2
• dump_binary/2
• from_unmanaged_to_managed/2
• from_managed_to_unmanaged/2

Optional functions to be defined by custom type:

• init_args/1

Basic Example

defmodule SimpleCustomTypeTwoBytesLong do
  use BinStructCustomType

  def parse_returning_options(bin, _custom_type_args, opts) do
    case bin do
      <<data::2-bytes, rest::binary>> -> {:ok, data, rest, opts}
      _ -> :not_enough_bytes
    end
  end

  def size(_data, _custom_type_args), do: 2
  def known_total_size_bytes(_custom_type_args), do: 2
  def dump_binary(data, _custom_type_args), do: data
  def from_unmanaged_to_managed(unmanaged, _custom_type_args), do: unmanaged
  def from_managed_to_unmanaged(managed, _custom_type_args), do: managed
endcopy