Defconst

This package provides defconst macro for defining a single constant and defenum macro for defining a list of enumerated constant values. The defined constants and enumerated constants are referencable in any expression as well as in guards statements.

Documentation is published at hexdocs.pm/defconst.

Requirements

Elixir ~> 1.15 (tested on 1.15–1.19 / OTP 26–28). The library has no runtime dependencies.

Installation

Defconst can be installed by adding defconst to your list of dependencies in mix.exs:

def deps do
  [
    {:defconst, "~> 0.4.0"}
  ]
end

Usage

defconst

Define ConstType1 module with constants

defmodule ConstType1 do
  use Defconst

  defconst :one, 1
  defconst :two, 2
end

Use ConstType1 module

defmodule ConstUse1 do
  require ConstType1

  def const_value(x) do
    case x do
      ConstType1.one -> "one"
      ConstType1.two -> "two"
    end
  end

  def const_guard(x) when x == ConstType1.two do
    "two"
  end
end

Introspection

Modules that use Defconst also expose:

• constants/0 — all constants as [{name, value}, ...]
• value_of/1 — the value for a constant name
• constant_of/1 — the constant name for a value (a list if several share the value, nil if none)

ConstType1.constants()        #=> [{:one, 1}, {:two, 2}]
ConstType1.value_of(:one)     #=> 1
ConstType1.constant_of(2)     #=> :two

defenum

Define EnumType1 module with default values

defmodule EnumType1 do
  use Defconst

  defenum [
    :zero,
    :one,
    :two
  ]
end

Use EnumType1 module

defmodule EnumUse1 do
  require EnumType1

  def enum_value(x) do
    case x do
      EnumType1.zero -> "zero"
      EnumType1.one -> "one"
      EnumType1.two -> "two"
      _ -> "unknown"
    end
  end

  def enum_guard(x) when x == EnumType1.two do
    "two"
  end
end

Define EnumType2 with specific values

defmodule EnumType2 do
  use Defconst

  defenum [
    {:one, 1},
    {:nine, 9},
    {:ten, "ten"}
  ]
end

Define EnumType3 using EnumGenerator3

defmodule EnumGenerator3 do
  @behaviour Defconst.Enum.Generator

  def next_value(_constant_name, previous_value) do
    previous_value <> previous_value
  end
end

defmodule TestEnumType3 do
  use Defconst

  defenum [
    {:one, "one"},
    {:nine, "nine"},
    :ten
  ],
  EnumGenerator3
end

Development

mix deps.get
mix test
mix format --check-formatted
mix credo --strict
mix dialyzer
mix docs

The toolchain is pinned in .tool-versions (Elixir 1.19.5 / OTP 28). CI runs the test suite across Elixir 1.15–1.19 / OTP 26–28, a formatting check, and a quality job (mix credo --strict + mix dialyzer).

Releasing

Releases are published to Hex automatically by CI (.github/workflows/release.yml):

1. Bump @version in mix.exs and update CHANGELOG.md; merge to main.
2. Sync and confirm the merged main carries the target version:

   git fetch origin --tags
   git show origin/main:mix.exs | grep '@version'   # expect the version you're releasing
   

3. Create the tag on the released commit and push it (don't let the Release UI auto-create the tag — that can place it on the wrong commit):

   git tag vX.Y.Z origin/main
   git push origin vX.Y.Z
   

4. Create the GitHub Release from that existing tag:

   gh release create vX.Y.Z --verify-tag --title "vX.Y.Z" --notes "See CHANGELOG.md"
   

5. CI (release.yml) re-verifies the tag matches mix.exs and runs mix hex.publish (package + docs).

This requires a HEX_API_KEY secret (a write-scoped Hex key) configured in the repository's Actions secrets.

License

Apache-2.0 — see LICENSE.