Question

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.

Answer 1

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