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Mehdi Farsi
I blog few times per week about Ruby - Paris

Numbers and Class Hierarchy in Ruby

In this article we’re going to explore the following topics:

  • the Numeric subclasses;
  • the Numeric ancestor chain.

The Numeric subclasses

The Numeric class is the highest class within the numeric classes family.

The following classes inherit directly from this class: Integer, Float, BigDecimal, Complex and Rational.

irb> require 'bigdecimal'
 => true
irb> Integer.superclass
 => Numeric
irb> Float.superclass
 => Numeric
irb> BigDecimal.superclass
 => Numeric
irb> Complex.superclass
 => Numeric
irb> Rational.superclass
 => Numeric

This class contains a common bunch of methods for:

  • math operations
  • rounding numbers

and a bunch of predicate methods as zero?, negative?, etc..

The definition of some operators —such as the / — are left to each subclass.

irb> 1.class
 => Integer
irb> Integer.superclass
 => Numeric
irb> Numeric.instance_methods(false).include?(:/)
 => false
irb> Integer.instance_methods(false).include?(:/)
 => true

Here, 1 is a single immutable object which is an instance of Integer.

We can see that the Numeric class doesn’t define any / instance method.

In contrary, the Integer class defines a / instance method.

The Numeric ancestor chain

As we can see, the Numeric class is a very important one, as it’s the common base of any numeric classes in Ruby.

So let’s break down its ancestor chain

irb> Numeric.ancestors
 => [Numeric, Comparable, Object, Kernel, BasicObject]
irb> Numeric.included_modules
 => [Comparable, Kernel]

The Numeric class inherit from the default Object class.

It also includes the Comparable module which is in charge of adding a bunch of comparison operators to a class.

This class shares the exact same ancestor chain as the String class.

Feel free to read the Ruby Object Model article if you are unfamiliar with the Object class and the ancestor chain.
Feel free to read the Comparable module article if you are unfamiliar with the Comparable module.

Voilà !

Thank you for taking the time to read this post :-)

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Here is a link to my last article: The ENV Object.