+ @是什么意思作为ruby中的方法

I was reading some code and I saw something along the lines of

我正在阅读一些代码,我看到了一些类似的东西

module M
  def +@
    self
  end
end

I was surprised that this was legal syntax, yet when I ran ruby -c on the file (to lint) it said it was valid. -@ was also a legal method name yet when I tried *@ or d@ both of those were illegal. I was wondering what +@ means and why is it legal?

我很惊讶这是合法的语法,但当我在文件上运行ruby -c(对于lint)时,它说它是有效的。 - @也是一个合法的方法名称,但当我尝试* @或d @时,这些都是非法的。我想知道+ @是什么意思,为什么合法?

2 个解决方案

#1

Ruby contains a few unary operators, including +, -, !, ~, & and *. As with other operators you can also redefine these. For ~ and ! you can simply just say def ~ and def ! as they don't have a binary counterpart (e.g. you cannot say a!b).

Ruby包含一些一元运算符,包括+, - ,!,〜,&和*。与其他运营商一样,您也可以重新定义这些运营商。对于〜和!你可以简单地说def~和def!因为他们没有二元对应物(例如你不能说a!b)。

However for - and + there is both a unary, and a binary version (e.g. a+b and +a are both valid), so if you want to redefine the unary version you have to use def +@ and def -@.

但是对于 - 和+有一元和二元版本(例如+ + b和+ a都有效),所以如果你想重新定义一元版本,你必须使用def + @和def - @。

Also note that there is a unary version of * and & as well, but they have special meanings. For * it is tied to splatting the array, and for & it is tied to converting the object to a proc, so if you want to use them you have to redefine to_a and to_proc respectively.

另请注意,*和&有一元版本,但它们有特殊含义。因为*它与splatting数组相关联,并且它与将对象转换为proc绑定在一起,因此如果要使用它们,则必须分别重新定义to_a和to_proc。

Here is a more complete example showing all kinds of the unary operators:

这是一个更完整的示例,显示了各种一元运算符:

class SmileyString < String
  def +@ 
    SmileyString.new(self + " :)")
  end

  def -@ 
    SmileyString.new(self + " :(")
  end

  def ~ 
    SmileyString.new(self + " :~")
  end

  def !
    SmileyString.new(self + " :!")
  end

  def to_proc
    Proc.new { |a| SmileyString.new(self + " " + a) }
  end

  def to_a
    [SmileyString.new(":("), self]
  end
end

a = SmileyString.new("Hello")
p +a                 # => "Hello :)"
p ~a                 # => "Hello :~"
p *a                 # => [":(", "Hello"]    
p !a                 # => "Hello :!"
p +~a                # => "Hello :~ :)"
p *+!-~a             # => [":(", "Hello :~ :( :! :)"]
p %w{:) :(}.map &a   # => ["Hello :)", "Hello :("]

In your example the Module just simply defines an unary + operator, with a default value of not doing anything with the object (which is a common behaviour for the unary plus, 5 and +5 usually mean the same thing). Mixing in with any class would mean the class immediately gets support for using the unary plus operator, which would do nothing much.

在你的例子中,模块只是简单地定义一个一元+运算符,其默认值是对对象没有做任何事情(这是一元加号的常见行为,5和+5通常意味着相同的事情)。混入任何类都意味着该类立即获得使用一元加运算符的支持,这将不会做任何事情。

For example (using ruby <=2.2):

例如(使用ruby <= 2.2):

module M
  def +@
    self
  end
end

p +"Hello"     # => NoMethodError: undefined method `+@' for "Hello":String

class String
  include M
end

p +"Hello"     # => "Hello"

Note that in this example you can clearly see from the error message that the +@ method is missing from the class

请注意,在此示例中,您可以从错误消息中清楚地看到类中缺少+ @方法

Note that the above example will be different from Ruby 2.3, as the unary minus and plus are defined for Strings since that version, and they refer to returning a frozen and unfrozen string from the original.

请注意,上面的示例与Ruby 2.3不同,因为从该版本开始为字符串定义了一元减号和加号,它们指的是从原始字符串返回冻结和未冻结的字符串。

#2

The method names +@ and -@ are used to overload the unary operators + and - in Ruby (1.9+). Unary operators are operators which only take a single value (e.g. value = -value).

方法名+ @和 - @用于在Ruby(1.9+)中重载一元运算符+和 - 。一元运算符是仅采用单个值的运算符(例如,value = -value)。

#1