Question

Possible Duplicate:
=== vs. == in Ruby

Fixnum == 2.class 
#=> true

Fixnum === 2.class
#=> false

why === doesn’t work? and how can I know the method .=== belong to(right now I guess it invoke the Object#==, or Object#===), but how can I make sure of that?

Answer 1

Duplicates:

• === vs. == in Ruby
• What does the "===" operator do in Ruby?
• === vs. == in Ruby
• Ruby compare objects

Case equality. See the documentation for Object#===. This method is usually overridden in subclasses of Object. For example, Module#===:

Case Equality–Returns true if anObject is an instance of mod or one of mod’s descendants. Of limited use for modules, but can be used in case statements to classify objects by class.

>> Module.new === Module
=> false
>> Module === Module.new
=> true

Regexp#=== is another one, in which case it’s a synonym of =~:

a = "HELLO"
case a
when /^[a-z]*$/; print "Lower case\n"
when /^[A-Z]*$/; print "Upper case\n"
else;            print "Mixed case\n"
end

An example in IRB:

>> "a" === /a/
=> false
>> /a/ === "a"
=> true

Remember, the first one returns false because you’re doing === on String which isn’t the same thing. In the second example we’re doing === on Regexp

And finally, Range is quite a good one it calls include? on the Range object and passes your value in:

>> (1..100) === 3
=> true
>> (1..100) === 300
=> false

For a list of these, check out RubyDoc.info core documentation and search for === in the methods area in the left side frame