Ruby compare objects [duplicate]

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=== 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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'===' 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.

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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. :)

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== is used for equality in conditional statements like if, unless, etc. === is used for determining equality in case statements.