[Ruby] Method to easily get the receiver type .class

This is a personal memo.

Class which refers to the class (type) of the receiver and superclass which confirms the parent class

Also about Basic Object.

table of contents

1. .class
2. .superclass
3. .BasicObject

1 .class

You can easily get the receiver class (type) by using the .class method.

python

x = 100

x.class 
=> Integer

python

str = "text"

str.class
=> String

python

obj = {:a=>1, :b=>2, :c=>3}

obj.class
=> Hash

python

arr = [1, 2, 3]

arr.class
=> Array

python

nil.class
=> NilClass

python

(1..4).class
=> Range

python

(1.23).class
=> Float

python

Class.class
=> Class

Class is an unnamed class. Called a metaclass. The class created with the class class name end has this Class.

python

class TestClass
  def hello
    msg = "test class"
    p "hello #{msg}"
  end
end

TestClass.class
=> Class

python

Kernel.class
=> Module

Kernel is a module that defines methods that can be referenced by all classes.

python

module TestModule
  def helloModule
    p "hello Module"
  end
end

TestModule.class
=> Module

It cannot be used for elements such as numbers, strings, arrays, hashes, nil, and modules.

It can be used for the type obtained by the class method.

What is a superclass?

The parent class is called the superclass.

python

class AAA
end

#Inherit class AAA
class BBB < AAA
end

When the class is inherited as described above, ** the parent class AAA becomes the superclass **.

BBB is called a subclass.

・ Class subclass name <superclass name

For Numeric

python

100.class
=> Integer

100.class.superclass
=> Numeric

100.class.superclass.superclass
=> Object

100.class.superclass.superclass.superclass
=> BasicObject

100.class.superclass.superclass.superclass.superclass
=> nil

Integer's superclass is Numeric. Numeric's superclass is Object.

python

#Error when used for numbers
100.superclass
NoMethodError (undefined method `superclass' for 100:Integer)

python

class Aaa
end

Aaa.class
=> Class

Aaa.superclass
=> Object

Object returns the superclass of Class.

When inherited

python

class Aaa
end

class Bbb < Aaa
end

BBB.superclass
=> Aaa

For module

You cannot use superclass for module.

python

module Xxx
end

Xxx.class
=> Module

Xxx.superclass
=> NoMethodError (undefined method 'superclass' for Xxx:Module)

Hierarchical structure of classes

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

In Ruby, all data is called an Object, and underneath it is a string of strings and a Numeric of numbers.

The higher you go, the more abstract and simple the definition becomes. BasciObject is the class at that time.

python

 BasicObject.superclass
=> nil