A Ractor-backed `Map` riffing on https://bugs.ruby-lang.org/issues/21121#note-1

map.rb

class Ractor
  module Channel
    def self.new(&block)
      channel = Ractor.new do
        loop do
          Ractor.yield Ractor.receive
        end
      end

      return block.call(channel) if block_given?

      channel
    end
  end
end

class Map
  def initialize
    @reactor = Ractor.new do
      cache = {}

      loop do
        channel, payload = Ractor.receive
        channel << cache.public_send(*payload)
      end
    end

    freeze
  end

  def []=(key, value)
    pipe __method__, key, value
  end

  %i[[] delete key? value?].each do |meth|
    define_method(meth) { |key| pipe meth, key }
  end

  %i[clear empty? keys length size to_a to_h values].each do |meth|
    define_method(meth) { pipe meth }
  end

  private

  def pipe(*payload)
    Ractor::Channel.new do |channel|
      @reactor << [channel, payload]
      channel.take
    end
  end
end