你如何覆盖 ruby​​ case 相等运算符?(===) [英] How do you override the ruby case equality operator? (===)

问题描述

我有一个类，我想在 case 语句中与字符串和符号进行比较，所以我认为我只是覆盖了我的类的 ===() 方法，一切都将是黄金.然而，我的 ===() 方法在 case 语句中永远不会被调用.有什么想法吗?

这是一些示例代码，以及在 irb 会话中发生的情况:

A 类定义初始化(x)@x=x #注意这个例子甚至不需要结尾def ===(其他)把在==="返回真结尾结尾

<块引用>

irb(main):010:0> a=A.new("hi")
=> #
irb(main):011:0> case a
irb(main):012:1> 当hi"然后 1
irb(main):013:1> 否则 2
irb(main):014:1> 结束
=> 2

(它从不打印消息，无论如何都应该返回 true)请注意，理想情况下我想做一个

def ===(其他)#puts "in ==="返回@x.===(其他)结尾

提前致谢.

解决方案

'case' 关键字后的表达式在 === 表达式的右侧，'when' 关键字后的表达式在左侧手边的表情.所以，被调用的方法是 String.===，而不是 A.===.

反转比较的快速方法:

class Revcomp定义初始化(对象)@obj = 对象结尾def ===(其他)其他 === @obj结尾def self.rev(obj)Revcomp.new(obj)结尾结尾课堂测试def ===(其他)把这里"结尾结尾t = 测试.new案例t当 Revcomp.rev("abc")把那里"别的把某处"结尾

I have a class that I want to compare to both strings and symbols in a case statement, so I thought that I just override the ===() method for my class and all would be gold. However my ===() method never gets called during the case statement. Any ideas?

Here is some example code, and what happens in a irb session:

class A
   def initialize(x)
      @x=x #note this isn't even required for this example
   end
   def ===(other)
      puts "in ==="
      return true
   end
end

irb(main):010:0> a=A.new("hi")
=> #
irb(main):011:0> case a
irb(main):012:1> when "hi" then 1
irb(main):013:1> else 2
irb(main):014:1> end
=> 2

(it never prints the message and should always return true anyway) Note that ideally I'd like to do a

def ===(other)
          #puts "in ==="
          return @x.===(other)
end

Thanks in advance.

解决方案

The expression after the 'case' keyword is the right hand side of the === expression, and the expression after the 'when' keyword is on the left hand side of the expression. So, the method that is being called is String.===, not A.===.

A quick approach to reversing the comparison:

class Revcomp
    def initialize(obj)
        @obj = obj
    end

    def ===(other)
        other === @obj
    end

    def self.rev(obj)
        Revcomp.new(obj)
    end
end

class Test
    def ===(other)
        puts "here"
    end
end

t = Test.new

case t
when Revcomp.rev("abc")
    puts "there"
else
    puts "somewhere"
end

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