>> class Left
>> def ===(other)
>> puts '=== on left'
>> end
>> end
=> nil

>> class Right
>> def ===(other)
>> puts '=== on right'
>> end
>> end
=> nil

>> l = Left.new
=> #<Left:0x111bd44>
>> r = Right.new
=> #<Right:0x1118f2c>
>> l === r
=== on left
=> nil

>> case l
>> when /blah/; puts 1
>> end
=> nil