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How do I check if a variable is an instance of a class?

Posted by: admin November 30, 2017 Leave a comment


In Java, you can do instanceof. Is there a Ruby equivalent?


It’s almost exactly the same. You can use Object‘s instance_of? method:

"a".instance_of? String # => true
"a".instance_of? Object # => false

Ruby also has the is_a? and kind_of? methods (these 2 are aliases, and work exactly the same), which returns true is one of the superclasses matches:

"a".is_a? String # => true
"a".is_a? Object # => true


kind_of? and is_a? are synonymous. They are Ruby’s equivalent to Java’s instanceof.

instance_of? is different in that it only returns true if the object is an instance of that exact class, not a subclass.


Have look at instance_of? and kind_of? methods. Here’s the doc link http://ruby-doc.org/core/classes/Object.html#M000372


I’ve had success with klass, which returns the class object. This seems to be Rails-specific.

Sample usage:

class Foo

# => Foo

Foo.new.klass == Foo
# => true

Foo.new.klass == "Foo"
# => false

There is also a method that accomplishes this: Object.is_a?, which takes the class object as an argument and returns true if self is an instance of the class or an instance of a subclass.