Ruby 元编程 类的真相
什么是对象：对象无非就是一组实例变量外加一个指向其类的引用。对象的方法并不存在与对象本身，而是存在与对象的类中。在类中，这些方法被称为类的实例方法
什么是类 ： 类无非是一个对象（class 的实例）外加一组实例方法和一个指向其超类的引用。Class类是Module类的子类，因此一个类也是一个模块
跟任何其他对象一样，类有自己的方法如new()，这些是Class的实例方法，跟其他类一样，需要引用才能用访问
1.Array.each_with_index
beikong-eshare(demo): irb
2.0.0p247 :001 > a=['1','a','b','c']=> ["1", "a", "java", "c"]
2.obj.instance_variables
2.0.0p247 :009 > class MyClass
2.0.0p247 :010?> def my_method
2.0.0p247 :011?> @v = 1
2.0.0p247 :012?> end
2.0.0p247 :013?> end
2.0.0p247 :017 > obj.instance_variables
=> [:@v]
2.0.0p247 :018 >
2.0.0p247 :019 > MyClass.instance_methods
=> [:my_method, :nil?, :===, :=~, :!~, :eql?, :hash, :<=>, :class, :singleton_class, :clone, :dup, :taint, :tainted?, :untaint, :untrust, :untrusted?, :trust, :freeze, :frozen?, :to_s, :inspect, :methods, :singleton_methods, :protected_methods, :private_methods, :public_methods, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :instance_of?, :kind_of?, :is_a?, :tap, :send, :public_send, :respond_to?, :extend, :display, :method, :public_method, :define_singleton_method, :object_id, :to_enum, :enum_for, :==, :equal?, :!, :!=, :instance_eval, :instance_exec, :__send__, :__id__]
2.0.0p247 :020 >
3.重访类
2.0.0p247 :022 > String.superclass
=> Object
2.0.0p247 :023 > Object.superclass
=> BasicObject
2.0.0p247 :024 > BasicObject.superclass
=> nil
2.0.0p247 :025 >
2.0.0p247 :026 > Class.superclass
=> Module
2.0.0p247 :027 > Module.superclass
=> Object
2.0.0p247 :028 >
4.常量的路径
2.0.0p247 :036 > module M
2.0.0p247 :037?> class C
2.0.0p247 :038?> X = "a constant"
2.0.0p247 :039?> end
2.0.0p247 :040?> C::X
2.0.0p247 :041?> end
=> "a constant"
2.0.0p247 :042 > module M
2.0.0p247 :043?> Y = 'another constant'
2.0.0p247 :044?> class C
2.0.0p247 :045?> ::M::Y
2.0.0p247 :046?> end
2.0.0p247 :047?> end
=> "another constant"
2.0.0p247 :048 > M.constants
=> [:C, :Y]
2.0.0p247 :054 > module M
2.0.0p247 :055?> class C
2.0.0p247 :056?> module M2
2.0.0p247 :057?> Module.nesting
2.0.0p247 :058?> end
2.0.0p247 :059?> end
2.0.0p247 :060?> end
=> [M::C::M2, M::C, M]
2.0.0p247 :061 >
5.调用一个方法是发生了什么
1.找到这个方法，称为方法查找 (向右一步，再向上)
2.0.0p247 :064 > Kernel.private_instance_methods
=> [:initialize_copy, :initialize_dup, :initialize_clone, :sprintf, :format, :Integer, :Float, :String, :Array, :Hash, :warn, :raise, :fail, :global_variables, :__method__, :__callee__, :__dir__, :eval, :local_variables, :iterator?, :block_given?, :catch, :throw, :loop, :respond_to_missing?, :trace_var, :untrace_var, :at_exit, :syscall, :open, :printf, :print, :putc, :puts, :gets, :readline, :select, :readlines, :`, :p, :test, :srand, :rand, :trap, :exec, :fork, :exit!, :system, :spawn, :sleep, :exit, :abort, :load, :require, :require_relative, :autoload, :autoload?, :proc, :lambda, :binding, :caller, :caller_locations, :Rational, :Complex, :set_trace_func, :gem, :gem_original_require]
2.0.0p247 :066 > Kernel.private_instance_methods.grep(/^pr/)
=> [:printf, :print, :proc]
2.0.0p247 :067 >
2.执行这个方法，Ruby需要一个self
一 如果调用方法的接受者不是你自己，则必须明确指明一个接受者
二 私有方法只能被隐含接受者调用
2.0.0p247 :067 > String.ancestors
=> [String, Comparable, Object, Kernel, BasicObject]
