Ruby on rails 在理解Ruby类的初始化(构造函数)中使用self和@in之间的区别时遇到困难
我正在努力阅读这本“基础扎实的红宝石作家”的书,我希望能澄清我对自我与@的理解 您可以使用“self.”创建一个简单的Ticket类来设置地点和日期。概括地说,我理解“self.”正在为Ticket的当前实例设置地点和日期,而@正在设置一个实例变量……但我不太确定为什么不使用实例变量呢 从只是玩弄它,两者似乎都是有效的,因为我可以在一个新的Ticket实例上使用@or self成功访问日期或地点Ruby on rails 在理解Ruby类的初始化(构造函数)中使用self和@in之间的区别时遇到困难,ruby-on-rails,ruby,initialization,instance,local-variables,Ruby On Rails,Ruby,Initialization,Instance,Local Variables,我正在努力阅读这本“基础扎实的红宝石作家”的书,我希望能澄清我对自我与@的理解 您可以使用“self.”创建一个简单的Ticket类来设置地点和日期。概括地说,我理解“self.”正在为Ticket的当前实例设置地点和日期,而@正在设置一个实例变量……但我不太确定为什么不使用实例变量呢 从只是玩弄它,两者似乎都是有效的,因为我可以在一个新的Ticket实例上使用@or self成功访问日期或地点 class Ticket attr_accessor :venue, :date def i
class Ticket
attr_accessor :venue, :date
def initialize(venue, date)
self.venue = venue
self.date = date
end
end
任何帮助我澄清我的理解将不胜感激 当您使用attr\u accessor:vention时,您实际上就是在这样做
def venue
@venue
end
def venue=(value)
@venue = value
end
当你做attr\u writer:vention
,你就是在做
def venue=(val)
@venue = val
end
def venue
@venue
end
当你做attr\u reader:vention
,你就是在做
def venue=(val)
@venue = val
end
def venue
@venue
end
请注意,@instance\u变量
在默认情况下为nil
,或者未初始化。要查看此操作,请在终端中键入irb
,然后按enter键。然后,键入一个@
,并在其后发送一组字符<代码>@ausdhyf934234092348将为零
当您在Ticket#initialize
中时,您作为对象的实例,因此self
将返回当前实例self.class
将返回该类,并允许您访问任何类级方法
class Ticket
VENUE_SIZES = [:small, :large]
def self.venue_sizes
VENUE_SIZES
end
def initialize(venue, date)
# ...
self.venue_sizes # NoMethodError
self.class.venue_sizes # [:small, :large]
end
end
在链的上游,如果您作为类而不是类的实例,则调用self.class
-或self.class.class
如果您作为实例,将返回class
attr\u accessor
只是语法上的糖;之所以这样做,是因为需要一次又一次地编写那些getter/setter方法。还有一些更酷的问题需要解决,比如用Ruby编写我们自己的nadnerb\u访问器
(尽管attr\u访问器
是用C实现的):
舱单
def self.nadnerb_存取器(*名称)
名字。每个人都有名字|
定义方法(名称)do
实例_变量_get(:“@#{name}”)
结束
定义_方法(“#{name}=”)do|值|
实例变量集(:“@#{name}”,值)
结束
结束
结束
纳德纳布大学观众:地点:价格
def初始化(场地、价格)
self.地点
self.price=价格
结束
def检查
"#"
结束
结束
票证=新票证(“StackOverflow”,“5美元”)
检查
基本相同,但一个被视为变量(@),另一个被视为方法(多亏了getter和setter)示例4“揭晓诀窍”。 我希望以下例子可以不言自明:
例1
例2
class Ticket
@@double_arroba = 'class variable' # class variable
attr_accessor :venue
def initialize(venue)
self.venue = venue
end
def whats_self?
p self # instance itself
end
def venue_self
p self.venue # instance itself calling its variable
end
def venue_arroba
p @venue # instance variable directly
end
def whats_double_arroba # instance method using a class variable
p @@double_arroba
end
def self.whats_double_arroba # class method using a class variable
p @@double_arroba
end
def self.whats_self? # class method calling itself
p self
end
end
ticket = Ticket.new('Broadway') # this is an instance of Ticket
p ticket #=> #<Ticket:0x007fb3fb0f1868 @venue="Broadway">
ticket.whats_self? #<Ticket:0x007fb3fb0f1868 @venue="Broadway">
p ticket.venue #=> "Broadway" #thanks to attr_accessor
ticket.venue_self #=> "Broadway"
ticket.venue_arroba #=> "Broadway"
ticket.whats_double_arroba #=> "class variable"
Ticket.whats_double_arroba #=> "class variable"
Ticket.whats_self? #=> Ticket
class Ticket
# attr_accessor :venue #comment out attr_accessor
def initialize(venue)
# self.venue = venue # venue method is not defined
@venue = venue # so you need to use @
end
def venue_self
# p self.venue # not working, self method is not available is nota available
end
def venue_arroba
p @venue # instance variable directly
end
end
ticket = Ticket.new('Broadway') # this is an instance of Ticket
p ticket #=> #<Ticket:0x007fb3fb0f1868 @venue="Broadway">
# p ticket.venue # does not work, no access
ticket.venue_self #=> nil, because commented the method code
ticket.venue_arroba #=> "Broadway"
# ticket.whats_double_arroba # not working
# class with getter and setter
class Ticket
def venue=(value) # setter (attr_reader)
@venue = value
end
def venue # getter (attr_writer)
@venue
end
def self_venue
self.venue # (*) you can omit self and write just venue
end
end
ticket = Ticket.new # ticket is the instance
ticket.venue="Brodway" # setter method .venue= in action
p ticket.venue #=> "Brodway" # getter method .venue in action
p ticket.self_venue #=> "Brodway" # calls the method .self_venue on the instance, which calls the getter method .venue (*)
# or write simply this code below, to let ruby build itself getter and setter
class Ticket
attr_accessor :venue
end