Possible Duplicate:
=== vs. == in Ruby
I was wondering what the difference is between the == and the === comparison in Ruby? What is the general definition of when to use which?
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1Possible duplicate : http://stackoverflow.com/questions/3422223/vs-in-ruby | None they are not related. One is equality the other is subsumption. – phwd Mar 08 '11 at 08:37
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@Philippe You are right that would have been my answer but I couldn't find it when I searched for it.. – Mark Mar 08 '11 at 09:20
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No worries, I found it by luck ... I was testing different ways to search for characters here. – phwd Mar 08 '11 at 09:53
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This is a duplicate of [What does the “`===`” operator do in Ruby?](http://StackOverflow.Com/q/4467538/#4467823) and [`===` vs. `==` in Ruby](http://StackOverflow.Com/q/3422223/#3422349). – Jörg W Mittag Mar 08 '11 at 18:11
3 Answers
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'===' is a broader (weaker) notion than the equality '=='. '===' becomes true not only under equality, but also under notions such as, matching a regular expression, being an instance of a class, etc. Despite what sarnold says, I actually do use '===' as a shorthand for 'kind_of?'. Where A is a class,
A === a
can be used as a shorthand of
a.kind_of?(A)
One thing to be careful is that, despite its appearance, it is not commutative. So,
a === A
will not work as intended.
sawa
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You never actually call === yourself. The language calls === behind the scenes when you're using case statements: http://www.skorks.com/2009/08/how-a-ruby-case-statement-works-and-what-you-can-do-with-it/
If you want different behavior for a class in case statements than the standard Object#=== provides, then you'll need to redefine it. But I've never really looked hard enough to find a reason to replace the standard definition. :)
sarnold
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== is used for equality in conditional statements like if, unless, etc. === is used for determining equality in case statements.
RubyFanatic
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