Crystal Classes — Inheritance, Abstract Classes, and Method Overrides

DodaTech Updated 2026-06-29 1 min read

In this tutorial, you will learn about Crystal Classes. We cover key concepts, practical examples, and best practices to help you master this topic.

Crystal has a single-inheritance class system with modules for mixins. Classes define behaviour and carry state through instance variables.

Class Basics

class Animal
  getter name : String

  def initialize(@name : String)
  end

  def speak : String
    "#{@name} makes a sound"
  end
end

class Dog < Animal
  def speak
    "#{@name} barks!"
  end
end

dog = Dog.new("Rex")
puts dog.speak  # => Rex barks!

Abstract Classes

abstract class Shape
  abstract def area : Float64
end

class Circle < Shape
  def initialize(@radius : Float64); end

  def area
    Math::PI * @radius * @radius
  end
end

← Previous Crystal Methods — Def, Return Types, Named Arguments and Blocks Next → Crystal HTTP Server — Building Web APIs with the Standard Library

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