A rough and naive declarative syntax for class reloading.

bouncy.rb

module Bouncy
  def self.mappings
    @@mappings ||= []
  end

  def self.bounce!
    mappings.each(&:bounce!)
  end

  def self.runner(const_name)
    lambda{|env|
      eval(const_name).call(env)
    }
  end

  class Middleware
    def initialize(app)
      @app = app
    end

    def call(env)
      Bouncy.bounce!
      @app.call(env)
    end
  end

  class Mapping
    attr_reader :constant, :path

    def self.add(*args)
      Bouncy.mappings << new(*args)
    end

    def initialize(constant, path)
      @constant = constant
      @path = path
    end

    def parent_const
      eval(constant.split("::")[-2] || "Object")
    end

    def const_name
      constant.split("::").last.to_sym
    end

    def load_path
      [File.dirname(__FILE__), path].join('/') + '.rb'
    end

    def bounce!
      parent_const.send :remove_const, const_name
      load load_path
    end
  end
end

def map(constant, path)
  Bouncy::Mapping.add(constant, path)
end

# and now the payoff....

map 'Some::Constant', 'some/constant'