Ruby on Rails: how do I check if a variable in an instance of a class?

Question

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

Answer 1

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

"a".instance_of?(String) # => true

Answer 2

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

Sample usage:

class Foo
end

Foo.new.klass
# => 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.

Answer 3

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

Answer 4

In Ruby, variables aren't objects, therefore they aren't instances of any classes und thus it doesn't make sense to check whether they are instances of any specific class.

Note that the same applies to Java, too: instanceof does not, as you claim, check if a variable is an instance of a class. It checks whether the object that the variable points to is an instance of a class. That is something completely different.