How to Get Object Type using kind_of, instance_of, and is_a In Ruby

1. Use the is_a to Check the Type of Object in Ruby
2. Use the kind_of? to Check the Type of Object in Ruby
3. Use the instance_of? to Check the Type of Object in Ruby

In Ruby, we may need to check the object type from time to time. Several methods accomplish this, including is_a, kind_of, and instance_of.

Use the is_a to Check the Type of Object in Ruby

Let’s start by making our class:

class Animal; end

dog = Animal.new

We can use is a? to determine the type of dog:

dog.is_a?(String)
# => false

dog.is_a?(Animal)
# => true

Dog is not a string. It’s an object of the Animal class.

The is a? method is interesting because it checks for the current class of an object and its ancestors.

It will return true if the object’s ancestors contain any class that matches the argument.

class Mammal < Animal; end

whale = Mammal.new

Whales are mammals that are also animals in the natural world. What was it like in Ruby?

Ruby excellently performs the necessary checks:

whale.is_a?(Mammal)
# => true

whale.is_a?(Animal)
# => true

Let’s take a look at the whales’ ancestors:

whale.class.ancestors

Output:

=> [Mammal, Animal, Object, Kernel, BasicObject]

Because Animal is present in the returned array, whale.is a?(Animal) is also true.

Use the kind_of? to Check the Type of Object in Ruby

The is_a? is an alias for kind of?.

dophin = Mammal.new

dophin.is_a?(Animal)
# => true
dophin.is_a?(Mammal)
# => true

Use the instance_of? to Check the Type of Object in Ruby

Unlike is a?, the instance of? does not check the object’s ancestors. If an object is an instance of the given class, it returns true; otherwise, it returns false.

cat = Mammal.new

cat.instance_of?(Mammal)
# => true

cat.instance_of?(Animal)
# => false