dry-rb/dry-core

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lib/dry/core/class_attributes.rb

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# frozen_string_literal: true

require "dry/core/constants"
require "dry/core/errors"

module Dry
  module Core
    # Internal support module for class-level settings
    #
    # @api public
    module ClassAttributes
      include Constants

      # Specify what attributes a class will use
      #
      # @example
      #  class ExtraClass
      #    extend Dry::Core::ClassAttributes
      #
      #    defines :hello
      #
      #    hello 'world'
      #  end
      #
      # @example with inheritance and type checking
      #
      #  class MyClass
      #    extend Dry::Core::ClassAttributes
      #
      #    defines :one, :two, type: Integer
      #
      #    one 1
      #    two 2
      #  end
      #
      #  class OtherClass < MyClass
      #    two 3
      #  end
      #
      #  MyClass.one # => 1
      #  MyClass.two # => 2
      #
      #  OtherClass.one # => 1
      #  OtherClass.two # => 3
      #
      # @example with dry-types
      #
      #  class Foo
      #    extend Dry::Core::ClassAttributes
      #
      #    defines :one, :two, type: Dry::Types['strict.int']
      #  end
      #
      # @example with coercion using Proc
      #
      #  class Bar
      #    extend Dry::Core::ClassAttributes
      #
      #    defines :one, coerce: proc { |value| value.to_s }
      #  end
      #
      # @example with coercion using dry-types
      #
      #  class Bar
      #    extend Dry::Core::ClassAttributes
      #
      #    defines :one, coerce: Dry::Types['coercible.string']
      #  end
      #
      def defines(*args, type: ::Object, coerce: IDENTITY) # rubocop:disable Metrics/PerceivedComplexity
        unless coerce.respond_to?(:call)
          raise ::ArgumentError, "Non-callable coerce option: #{coerce.inspect}"
        end

        mod = ::Module.new do
          args.each do |name|
            ivar = :"@#{name}"

            define_method(name) do |value = Undefined|
              if Undefined.equal?(value)
                if instance_variable_defined?(ivar)
                  instance_variable_get(ivar)
                else
                  nil
                end
              elsif type === value # rubocop:disable Style/CaseEquality
                instance_variable_set(ivar, coerce.call(value))
              else
                raise InvalidClassAttributeValue.new(name, value)
              end
            end
          end

          define_method(:inherited) do |klass|
            args.each { |name| klass.send(name, send(name)) }

            super(klass)
          end
        end

        extend(mod)
      end
    end
  end
end