[Ruby] How to use is_a? Differences from kind_of? and instance_of ?. How to check the type and return a boolean value.

A method that checks the element type and returns true if it matches the specified type, false if it is different,

About the difference between is_a?, kind_of?, Instance_of?.

table of contents

1. Usage and examples
2. Main type types
3. is_a? and kind_of? are the same
4. Difference between is_a? and instance_of?
5. What is a superclass?
6. Notes on using is_a?

· Receiver method (type)

Returns true if the receiver matches the type specified in the argument, false otherwise.

Example (is_a?）

arr = [1, 2, 3]

arr.is_a?(Array)
=> true

arr.is_a?(String)
=> false

Example (kind_of?）

arr = [1, 2, 3]

arr.kind_of?(Array)
=> true

arr.kind_of?(String)
=> false

Example (instance_of?）

arr = [1, 2, 3]

arr.instance_of?(Array)
=> true

arr.instance_of?(String)
=> false

Illustration

def _article_items
    if article_items.is_a?(Hash)
      [
        article_items.fetch('default') 
      ]
    elsif article_items.is_a?(Array)
      article_items
    else
      []
    end
  end

-Instance_of?: Evaluate only the receiver ・ Is_a?: Superclass type is also evaluated

A superclass is the parent class of the current element's class. is_a? returns true even if the argument contains a superclass type.

An example is as follows. (Details of superclass will be described later)

python

arr = [1, 2, 3]

arr.is_a?(Object)
=> true

arr.instance_of?(Object)
=> false

When Object, which is a superclass of Array, is used as an argument, is_a? is true and instance_of? is false.

Each element has a class, and the parent class of that class is the superclass.

For example

--Integer 1 class (type) is Integer. --The Integer superclass is Numeric, which represents all numbers. --Numeric's superclass is an Object that represents all the data. --The Object superclass is a BasicObject that has only basic functions such as identification and method specification. This is the highest class.

Hierarchical structure of classes

BasicObject
↓
Object
↓
String,　Numeric, Module, Class,,,
            ↓
     Integer, Floot

python

BasicObject.superclass
=> nil

** ▼ Caution 1 **

Note that it will be true even if you specify a superclass as an argument, so if you specify an Object or Basic Object that corresponds to all the data, true will be returned.

python

obj = {:a=>1, :b=>2, :c=>3}
obj.is_a?(BasicObject)
=> true

100.is_a?(BasicObject)
=> true

"String".is_a?(BasicObject)
=> true

python

class Aaa
end

##Class inheritance
class Bbb < Aaa
end

##Superclass class name is false
Bbb.is_a?(Aaa)
=> false

##If you specify the type, true is returned
Bbb.is_a?(Class)
=> true