Thanks @karlosmid and @Eiji ! I had not seen either of those libraries and are exactly what I was curious about, I’ll have to dig into them… we’re not likely to replace our in-house tool because we use it extensively and it works well, but, good to be aware of/make easier for others to discover from this discussion perhaps…

For what it’s worth/in case anyone is interested, here’s the code from our in homebrewed solution, including an extension for Absinthe integration and for supporting constraints in migrations via a versioning convention… for usage, you use the module defining a new Enum, and then import or require your enum module to expose the macros for usage in your code…

defmodule Optimizer.Ecto.Types.Enumerable do
  @moduledoc """
  Enumerable type for Ecto fields.  Main benefit vs Ecto.Enum being first class `values` and macro functions for each
  value so that compilation will fail if they are removed/renamed.

  NOTE:  if an enum is stored in the database, DO NOT simply drop a value,
  it should be deprecated first, then removed after a migration to remove the value from the database.
  deprecation is a new feature used via an optional keyword argument to the `use` macro, e.g.

  use Optimizer.Ecto.Types.Enumerable, values: [:foo, :bar], deprecated: [:baz]

  Based on:
  https://github.com/KamilLelonek/exnumerator/blob/2e72dd1a34e119e5198aebf18ebfb4bed77f3646/lib/exnumerable.ex
  """
  # credo:disable-for-this-file
  defmacro __using__(opts) do
    quote location: :keep,
          bind_quoted: [current_values: opts[:values], deprecated_values: opts[:deprecated] || []] do
      @behaviour Ecto.Type

      require Logger

      @impl Ecto.Type
      def type, do: :string
      def __current_values, do: unquote(current_values)
      def __values, do: unquote((current_values ++ deprecated_values) |> Enum.sort())

      # these are used in guards hence macros
      defmacro current_values, do: unquote(current_values)
      defmacro values, do: unquote((current_values ++ deprecated_values) |> Enum.sort())

      values = current_values ++ deprecated_values

      for value <- values, atom = value, string = Atom.to_string(value) do
        deprecated? = deprecated_values |> Enum.member?(value)

        downcased_atom =
          string
          |> String.downcase()
          |> String.to_atom()

        upcased_string = String.upcase(string)

        @impl Ecto.Type
        def cast(unquote(string)), do: {:ok, unquote(atom)}

        if upcased_string != string do
          def cast(unquote(upcased_string)), do: {:ok, unquote(atom)}
        end

        def cast(unquote(atom)), do: {:ok, unquote(atom)}

        @impl Ecto.Type
        if deprecated? do
          def load(unquote(string)) do
            Logger.warning(
              "Deprecated value #{unquote(string)} loaded for #{inspect(__MODULE__)}"
            )

            {:ok, unquote(atom)}
          end
        else
          def load(unquote(string)), do: {:ok, unquote(atom)}
        end

        @impl Ecto.Type
        if deprecated? do
          def dump(unquote(string)) do
            Logger.warning(
              "Deprecated value #{unquote(string)} dumped for #{inspect(__MODULE__)}"
            )

            {:ok, unquote(string)}
          end

          def dump(unquote(atom)) do
            Logger.warning("Deprecated value #{unquote(atom)} dumped for #{inspect(__MODULE__)}")
            {:ok, unquote(atom)}
          end
        else
          def dump(unquote(string)), do: {:ok, unquote(string)}
          def dump(unquote(atom)), do: {:ok, unquote(string)}
        end

        if deprecated? do
          defmacro unquote(downcased_atom)() do
            IO.warn(
              "Deprecated enum value #{unquote(downcased_atom)} used, please update code, this is only supported for legacy compatibility",
              Macro.Env.stacktrace(__ENV__)
            )

            unquote(atom)
          end
        else
          defmacro unquote(downcased_atom)(), do: unquote(atom)
        end
      end

      def cast(_), do: :error
      def load(_), do: :error
      def dump(_), do: :error

      def cast!(term) do
        case cast(term) do
          {:ok, value} ->
            value

          :error ->
            raise Ecto.CastError,
              message: "cannot cast #{inspect(term)} as #{inspect(__MODULE__)}"
        end
      end

      @impl Ecto.Type
      def embed_as(_), do: :self

      @impl Ecto.Type
      def equal?(value_1, value_2), do: value_1 === value_2
    end
  end
end

and our absinthe EnumBuilder

defmodule EnumBuilder do
  @moduledoc """
  This module is used to dynamically build an enum type for the GraphQL schema.
  """

  alias Absinthe.Blueprint
  alias Absinthe.Blueprint.Schema
  alias Absinthe.Schema.Notation
  alias Absinthe.Type.Deprecation

  @spec run(Blueprint.t(), atom(), module()) :: Blueprint.t()
  def run(blueprint = %Blueprint{}, name, enum_module) do
    %{schema_definitions: [schema]} = blueprint

    new_enum = build_dynamic_enum(enum_module, name)

    new_schema = %{schema | type_definitions: [new_enum | schema.type_definitions]}

    %{blueprint | schema_definitions: [new_schema]}
  end

  defp build_dynamic_enum(enum_module, name) do
    %Schema.EnumTypeDefinition{
      name: name |> Atom.to_string() |> Absinthe.Utils.camelize(),
      identifier: name,
      module: __MODULE__,
      __reference__: Notation.build_reference(__ENV__),
      values: values(enum_module)
    }
  end

  defp values(enum_module) do
    # require enum_module
    {current_values, values} = extract_module_values(enum_module)

    for value <- values do
      deprecated? = value not in current_values

      define_value(
        value,
        String.upcase("#{value}"),
        enum_value_description(enum_module, value),
        deprecated?
      )
    end
  end

  defp extract_module_values(enum_module) do
    {
      enum_module.__current_values(),
      enum_module.__values()
    }
  end

  defp enum_value_description(enum_module, value) do
    if function_exported?(enum_module, :to_description, 1) do
      enum_module.to_description(value)
    else
      nil
    end
  end

  defp define_value(key, name, description, deprecated?) do
    %Schema.EnumValueDefinition{
      identifier: key,
      value: key,
      name: name,
      description: description,
      deprecation:
        if deprecated? do
          %Deprecation{reason: "deprecated"}
        else
          nil
        end,
      module: __MODULE__,
      __reference__: Notation.build_reference(__ENV__)
    }
  end

  defmacro __using__(_options) do
    quote do
      Module.register_attribute(__MODULE__, :dynamic_enums, accumulate: true, persist: true)
      @before_compile unquote(__MODULE__)
      import unquote(__MODULE__)
    end
  end

  defmacro __before_compile__(_env) do
    quote do
      def __all_dynamic_enums__ do
        @dynamic_enums
      end
    end
  end

  defmacro dynamic_enum(enum_identifier, enum_module) do
    %{module: mod} = __CALLER__

    quote bind_quoted: binding() do
      Module.put_attribute(mod, :dynamic_enums, {enum_identifier, enum_module})
    end
  end
end

and middleware

defmodule DynamicEnumCreationPhase do
  @moduledoc """
  based on Absinthe phases https://hexdocs.pm/absinthe/1.5.0/Absinthe.Phase.html
  """
  alias Absinthe.Blueprint
  alias Absinthe.Pipeline
  alias Absinthe.Phase

  @behaviour Phase

  @spec get_module :: __MODULE__
  def get_module, do: __MODULE__

  @spec pipeline(Pipeline.t()) :: Pipeline.t()
  def pipeline(pipeline) do
    Pipeline.insert_after(pipeline, Phase.Schema.TypeImports, __MODULE__)
  end

  @impl Phase
  def run(blueprint = %Blueprint{}, _) do
    {:ok,
     Enums.__all_dynamic_enums__()
     |> Enum.reduce(blueprint, fn {identifier, enum_module}, acc ->
       EnumBuilder.run(acc, identifier, enum_module)
     end)}
  end
end

We also add in our repo.ex file, though this is purely optional/we use less now than we used to

  @spec create_enum_constraint(atom | binary, any, :array | :string, maybe_improper_list) :: %{
          :__struct__ => Ecto.Migration.Constraint | Ecto.Migration.Index | Ecto.Migration.Table,
          :prefix => any,
          optional(any) => any
        }
  def create_enum_constraint(table, field, field_type, enum_list) when is_list(enum_list) do
    check = build_enum_constraint_check(field, enum_list, field_type)

    Migration.create(Migration.constraint(table, :"valid_#{field}", check: check))
  end

  @spec drop_enum_constraint(atom | binary, any) :: %{:prefix => any, optional(any) => any}
  def drop_enum_constraint(table, field) do
    Migration.drop(Migration.constraint(table, :"valid_#{field}"))
  end

  defp build_enum_constraint_check(field, enum_list, :string) do
    "#{field} ~ '^(#{Enum.join(enum_list, "|")})$'"
  end

  defp build_enum_constraint_check(field, enum_list, :array) do
    array = form_array_string(enum_list, [])

    ~s(#{field} <@ ARRAY[#{array}])
  end

  defp form_array_string([head | []], acc) do
    [wrap_in_io_list(head, false) | acc]
    |> Enum.reverse()
    |> to_string()
  end

  defp form_array_string([head | tail], acc) do
    form_array_string(tail, [wrap_in_io_list(head) | acc])
  end

  defp wrap_in_io_list(val, trailing_comma? \\ true) do
    initial =
      if trailing_comma? do
        [","]
      else
        []
      end

    [[~S('), to_string(val), ~S(')] | initial]
  end

Could publish as a library, but, not a ton of code and not sure how it compares yet to above existing libraries I wasn’t aware of so just throwing out there for feedback/interest

I do recall looking at typedstruct at some point and its nice it saves some typing and all, but, I’m not sure if I realized the direction it went, allowing you to use types in your struct definition as opposed to saving you tying up a type for your struct… that’s interesting… but given the direction of Elixir’s support for static typing more directly in the language, I’m not likely to start taking up a tool now that relies on the… what I’ll call deprecated type syntax? Since my understanding is there may be support for migrating that to the new type system, but the syntax and behavior will definitely be different.

But while the compile time errors there are nice, it does nothing to address use of the values elsewhere in code, as in my experience when you have enums, you need to reference specific values in multiple places, and one of the things I find inadequate about Ecto.Enum is it doesn’t help you do that in a DRY or safe way protecting from typos etc… our module (mostly) does, as long as its used “correctly”…

GitHub - gjaldon/ecto_enum: Ecto extension to support enums in models · GitHub works pretty well for my needs. And it generates functions that allow you to use the enums elsewhere in the codebase, e.g.

iex> MyApp.SomeEnum.valid_value?("standard")
true
iex> MyApp.SomeEnum.valid_value?("bogus_value")
false