红宝石中`nil`私有方法的目的是什么？

使用ruby 2.3和pry REPL,我有这个有趣的结果,我无法理解:

nil.private_methods
# [:DelegateClass, :Digest, :sprintf, :format, :Integer, :Float, :String, :Array, :Hash, :throw, :iterator?, :block_given?, :catch, :loop, :Rational, :trace_var, :untrace_var, :Complex, :at_exit, :gem_original_require, :URI, :set_trace_func, :select, :caller, :caller_locations, :test, :fork, :`, :exit, :sleep, :respond_to_missing?, :load, :exec, :exit!, :syscall, :open, :printf, :print, :putc, :puts, :readline, :readlines, :p, :abort, :gets, :system, :spawn, :proc, :lambda, :srand, :pp, :rand, :initialize_copy, :initialize_clone, :initialize_dup, :Pathname, :trap, :gem, :BigDecimal, :require, :require_relative, :autoload, :autoload?, :binding, :local_variables, :warn, :raise, :fail, :global_variables, :__method__, :__callee__, :__dir__, :eval, :method_missing, :singleton_method_added, :singleton_method_removed, :singleton_method_undefined, :initialize]

看起来好像那些私有方法链接到加载的模块:

methods = nil.private_methods.dup
require "json"
nil.private_methods - methods
# [:j, :JSON, :jj]

我想知道这些私人方法的目的,并没有在互联网上找到任何相关的东西.

NilClass不会自己声明任何私有实例方法.他们来自Kernel和BasicObject:

NilClass.ancestors
#? [NilClass, Object, PP::ObjectMixin, Kernel, BasicObject]
NilClass.private_instance_methods -
  (NilClass.ancestors - [NilClass]).flat_map(&:private_instance_methods)
#? []

任何ruby类都源自BasicObject并包含Kernel.

另外,Module#private_instance_methods接受boolean参数,当设置为false:时,它禁止继承方法的输出:

NilClass.private_instance_methods false
#? []

JSON另一方面,猴子补丁NilClass在所有其他类别中:

require 'json'
NilClass.ancestors
#? [NilClass, JSON::Ext::Generator::GeneratorMethods::NilClass,
#   Object, JSON::Ext::Generator::GeneratorMethods::Object,
#   PP::ObjectMixin, Kernel, BasicObject]