exception_classes.rb

class WrappedError
  def initialize(error)
    @error = error
  end

  def exception
    @error.exception
  end
end

class CustomError < StandardError
end

begin
  raise WrappedError.new(CustomError.new)
rescue CustomError
  puts 'got custom error'
end

begin
  raise WrappedError.new(CustomError.new)
rescue WrappedError
  puts 'got wrapped error' # it does not happen!
end