Module: Kernel::Enum

Defined in:
lib/patch/enum.rb

Overview

The Enum module provides a factory method [] to dynamically create simple, lightweight enum-like classes. These classes allow defining a set of named constants with associated numeric values.

Enums are defined by passing symbols, strings, or hashes to the [] method.

Usage examples:

OS = Enum[:Arch, :BSD] # OS.Arch => 0, OS.BSD => 1
Bool = Enum[nil: 1, :t 10] # Bool.nil => 1, Bool.t => 10
Way = Enum["↑", { ↓: 50 }, :→ ] # Way.↑ => 0, Way.↓ => 50, Way.→ => 51
Pet = Enum[:Dog, :Cat] { |v| 0.5 * v } # Pet.Dog => 0.0, Pet.Cat => 0.5

The generated enum class provides:

  • Class methods to access each constant’s value (e.g., Way.↑).

  • A size method to get the number of defined constants.

  • An each class method to iterate over value-name pairs.

  • A to_h class method to get a hash of name-value pairs.

Class Method Summary collapse

Class Method Details

.[](*args, &block) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/patch/enum.rb', line 20

def self.[](*args, &block)
  # At least one argument should be provided
  raise ArgumentError, "Enums must have at least one constant" if args.empty?

  # Initialize tracking variables
  pairs = {}
  current = 0

  args.flatten!(1)

  # Process all arguments to extract name-value pairs
  args.each do |arg|
    current = case arg
      when Symbol, String
        # Single enum value - assign current value and increment
        pairs[arg.to_sym] = current
        current + 1
      when Hash
        # Hash with explicit key-value mapping
        arg.each do |key, value|
          unless key.is_a?(Symbol) || key.is_a?(String)
            raise ArgumentError, "Enum names must be Symbol|String: #{key.inspect}"
          end
          raise ArgumentError, "Enum values must be Numeric: #{value.inspect}" unless value.is_a?(Numeric)
          pairs[key.to_sym] = value
          current = value + 1
        end

        current
      else
        raise ArgumentError, "Invalid enum argument: #{arg.inspect}"
      end
  end

  # Apply block transformation if provided
  if block_given?
    values = Set.new
    pairs.each do |prop, value|
      hash = block.call(value, prop)

      # Make sure block result is Numeric
      unless hash.is_a?(Numeric)
        raise ArgumentError, "Block must return a Numeric, got #{hash.class}: #{hash.inspect}"
      end

      # Check that result is unique
      if values.include?(hash)
        raise ArgumentError, "Block must return unique values, duplicate: #{hash}"
      end

      values.add(hash)
      pairs[prop] = hash
    end
  end

  # Create enum class and include this module
  klass = Class.new
  klass.include(Enum)

  # Store enums data for instance methods
  klass.instance_variable_set(:@pairs, pairs.freeze)

  # Define getter methods for each constant
  pairs.each do |prop, value|
    begin
      klass.define_singleton_method(prop) { value }
    rescue => e
      raise ArgumentError, "Invalid const name '#{prop}': #{e.message}"
    end
  end

  klass.define_method(:initialize) do
    raise RuntimeError, "Enums are not meant to be instantiated"
  end

  # Define utility methods directly on the class
  klass.define_singleton_method(:size) do
    @pairs.size
  end

  klass.define_singleton_method(:to_h) do
    @pairs.dup
  end

  klass.define_singleton_method(:each) do |&block|
    return enum_for(:each) unless block

    @pairs.each do |prop, value|
      block.call(value, prop)
    end
  end

  klass
end