A completely stupid example of how to implement classes/objects in Ruby with Procs and Proc#method_missing

functional_object_spec.rb

class Proc
  def method_missing(name, *args)
    self[name, *args]
  end
end

MyCrazyClass = ->(message, *args) {
  case message
  when :new
    ->(message, *args) {
      case message
      when :foo
        "foo"
      when :upcase
        args.first.upcase
      end
    }
  else
    raise NoMethodError.new
  end
}

describe MyCrazyClass do
  it "responds to new" do
    expect {
      MyCrazyClass.new
    }.to_not raise_error
  end

  it "does not respond to arbitrary messages" do
    expect {
      MyCrazyClass.foobarbazquux
    }.to raise_error(NoMethodError)
  end
end

describe MyCrazyClass do
  subject { MyCrazyClass.new }

  its(:foo) { should eq "foo" }
  
  it "can upcase strings" do
    subject.upcase("a string").should eq "A STRING"
  end
end