Top Level Environment and Object main in Ruby

本文只是将有关ruby top level environment 和main Object的sample进行简单比较，仔细看完比较的结果后您自然会得结论。

运行环境是在文件中，与irb运行环境在某些地方会有出入，请参照http://www.iteye.com/topic/125046

1.top level environment 中默认receiver是一个叫main的Object

 

p self#main
p self.class#Object

 2.默认情况，在top level environment定义的方法称为main的私有方法，在irb中貌似默认是public method。

 

def m
end
p self.singleton_methods(false).include? "m" #false
p Object.singleton_methods(false).include? "m" #false
p self.methods(false).include? "m" #false
p self.public_methods(false).include? "m" #false
p self.private_methods(false).include? "m"#true
p Object.instance_methods(false).include? "m" #false
p Kernel.private_methods(false).include? "m" #false

 

3.top level environment可以和像在普通类中一样用public声明方法定义，并且被public声明后称为所有Object实例的public method

 

public
def m
end
p self.singleton_methods(false).include? "m" #false
p Object.singleton_methods(false).include? "m" #false
p self.methods(false).include? "m" #false
p self.public_methods(false).include? "m" #true
p self.private_methods(false).include? "m"#false
p Object.instance_methods(false).include? "m" #true
p Kernel.private_methods(false).include? "m" #false

 4.和在一般class中一样，局部变量不能被top level方法调用。

 

var="hooopo"
def get_var
  p var
end
get_var #in `get_var': undefined local variable or method `var' for main:Object (NameError)

 5.和在一般class中一样，top level定义的实例变量可以被top level中的方法调用。

 

@var="hooopo"
def get_var
  p @var
end
get_var #"hooopo"

 6.在top level定义的实例变量属于默认receiver main Object，并且不属于任何非main Object的Object。

 

@var="hooopo"
obj=Object.new
p obj #=>#<Object:0x2a62f64>
p self #=>#<Object:0x494f9e0 @var="hooopo">

 7.top level中定义的类变量成为Object的类变量，由于类变量可以被继承到子类，并且被子类改变，才有了慎用类变量 - 实例变量靠谱量又足

中“类变量(@@xx)的问题在于它本质跟全局变量一样”的说法。。

 

@@var="hooopo"
def Object.get_var_in_obj
  p @@var
end
class String
  def String.get_var_in_str
    class_variable_get("@@var")
  end
  def String.set_var_in_str
    class_variable_set("@@var","hooopo is changed")
  end
end
Object.get_var_in_obj #"hooopo"
p Object.class_variables #["@@var"]
p String.class_variables #["@@var"]
p String.get_var_in_str #"hooopo"
String.set_var_in_str
p @@var #"hooopo is changed"

 8.全局变量是名副其实的全局变量，无论是在top level还是class中定义，都可以被获取。

 

$var="hooopo"
def get_var
  p $var
end
get_var #"hooopo"
class C
  $var_c="Hooopo"
  def get_var
    p $var_c
  end
end
p $var_c #"hooopo"
c=C.new #"hooopo"
c.get_var #"Hooopo"
p $var_c #"Hooopo"

 9.可以为main Object定义单体方法...

 

class << self
  def m
    p "singleton method of top-level Object instance"
  end
end
m#"singleton method of top-level Object instance"
self.m #"singleton method of top-level Object instance"
o=Object.new
o.m # undefined method `m' for #<Object:0x2a62dfc> (NoMethodError)

 10.main Object的单体方法调用优先于instance method。

 

def m
  p "instance method of top level Object instance"
end
class << self
  def m
    p "singleton method of top-level Object instance"
  end
end
m#"singleton method of top-level Object instance"
self.m #"singleton method of top-level Object instance"

 11.top level环境更像是在一个类中...

 

def m
  p "instance method of top level Object instance"
end
#class << self
 # def m
 #   p "singleton method of top-level Object instance"
 # end
#end
m#"instance method of top level Object instance"
self.m #private method `m' called for main:Object (NoMethodError)

 12.public声明，让top level方法真正top level

 

public
def m
  p "instance method of top level Object instance"
end
#class << self
 # def m
 #   p "singleton method of top-level Object instance"
 # end
#end
m#"instance method of top level Object instance"
self.m #"instance method of top level Object instance"

 13.在类中可以调用top level method

 

def top_level_method
  p "hooopo"
end
class C
  def instance_method_of_c
    top_level_method
  end
end
c=C.new
c.instance_method_of_c #"hooopo"

 13.同11

 

def top_level_method
  p "hooopo"
end
class C
  def instance_method_of_c
    self.top_level_method
  end
end
c=C.new
c.instance_method_of_c #`instance_method_of_c': private method `top_level_method' called for #<C:0x2a62d34> (NoMethodError)

 14.优先级问题，类中实例方法优先于top level 方法

public

def top_level_method

  p "hooopo"
end
class C
  def top_level_method
    p "hooopo-in instance method of C"
  end
  def instance_method_of_c
    top_level_method
  end
end
c=C.new
c.instance_method_of_c #"hooopo-in instance method of C"

 15.优先级问题，类中实例方法优先于top level 方法，也优先于Kernel模块中方法

def puts
  STDOUT.puts "from top level"
end
class C
  def puts
    STDOUT.puts "from insctance method of C"
  end
  def self.puts
    STDOUT.puts "from sington method of C"
  end
  def call_puts
    puts
  end
end
c=C.new
c.call_puts #from insctance method of C

 16.top level中方法优先于Kernel模块中的方法。

 

def puts
  STDOUT.puts "from top level"
end
class C
  #def puts
  #  STDOUT.puts "from insctance method of C"
  #end
  def self.puts
    STDOUT.puts "from sington method of C"
  end
  def call_puts
    puts
  end
end
c=C.new
c.call_puts #from top level

 17.同16

 

#def puts
#  STDOUT.puts "from top level"
#end
class C
  #def puts
  #  STDOUT.puts "from insctance method of C"
  #end
  def self.puts
    STDOUT.puts "from sington method of C"
  end
  def call_puts
    puts
  end
end
c=C.new
c.call_puts #"\n"=>from Kernel?

18. 关于main Object 实现的猜测：

 

class Object
  Object.new.instance_eval do
    def self.to_s
      "main"
    end
   private
    ##
    # Your program gets inserted here...
    ##

  end
end

  

还有就是top level 常量的问题

irb(main):001:0> CONST="HOOOPO"
=> "HOOOPO"
irb(main):002:0> class T
irb(main):003:1>  CONST="hooopo"
irb(main):004:1>  def get_top_level_const
irb(main):005:2>   ::CONST
irb(main):006:2>  end
irb(main):007:1>  def get_class_const
irb(main):008:2>    CONST
irb(main):009:2>  end
irb(main):010:1> end
=> nil
irb(main):011:0> t=T.new
=> #<T:0x496e200>
irb(main):012:0> t.get_top_level_const
=> "HOOOPO"
irb(main):013:0> t.get_class_const
=> "hooopo"
irb(main):014:0> ::CONST
=> "HOOOPO"