一元运算符的行为 [英] Unary operators behavior

问题描述

在Ruby上的Fixnum类上重新定义一元+运算符时，出现了一些奇怪的结果.不确定原因为何发生(特别是009行).

Had some weird results when redefining the unary + operator in Ruby on the Fixnum class. Not exactly sure why things are happening the way they are (specifically line 009).

irb:003> class Fixnum
irb:004>   def +@ #define unary +
irb:005>     15
irb:006>   end
irb:007> end
=> nil
irb:008> 2
=> 2
irb:009> +2
=> 2
irb:010> +(2)
=> 15
irb:011> ++2
=> 15

推荐答案

我怀疑您在解析器解释数字文字时看到了解析器行为的副作用.

I suspect you're seeing a side effect of the parser's behavior in how it interprets numeric literals.

如果我们创建自己的类:

If we create our own class:

class C
  def +@
    11
  end
end

然后看一些事情:

> c = C.new
> +c
 => 11 
> ++c
 => 11 

这正是我们期望发生的事情.如果我们使用您的Fixnum一元+覆盖和Fixnum变量:

That's exactly what we expect to happen. If we use your Fixnum unary + override and a Fixnum variable:

> n = 23
> +n
 => 15 
> ++n
 => 15 

然后我们再次看到您的期望.在这两种情况下，我们都看到对非文字对象调用+@方法的结果.

then again we see what you're expecting. In both cases, we see the result of calling the +@ method on a non-literal.

但是当我们在您的操作员就位的情况下查看+6时:

But when we look at +6 with your operator in place:

> +6
 => 6 

+@方法未调用.同样，如果我们覆盖-@:

the +@ method is not called. Similarly if we override -@:

class Fixnum
  def -@
    'pancakes'
  end
end

并查看其作用:

> -42
 => 42

那么这是怎么回事?好吧，Ruby看到+6和-42并不是作为6.send(:+@)和42.send(:-@)方法调用，而是作为正6和负42的单个文字.

So what's going on here? Well, Ruby is seeing +6 and -42 not as 6.send(:+@) and 42.send(:-@) method calls but as single literals for positive six and negative forty-two.

如果您开始添加括号+(6)和-(42)，则Ruby会看到非文字表达式并最终调用一元方法.同样，当您将一元运算符加倍时.

If you start adding parentheses, +(6) and -(42), then Ruby sees non-literal expressions and ends up calling the unary methods. Similarly when you double the unary operators.

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