Programming Crystal

Applying Inheritance

As in all object-oriented languages and much the same as in Ruby, Crystal provides for single inheritance, indicated by: subclass < superclass. Putting properties and methods common to several classes into a superclass lets them all share functionality. That way, you can use all instance variables and all methods of the superclass in the subclass, including the constructors. You can see this in the following example where PDFDocument inherits initialize, name, and print from Document:

classes_and_structs/inheritance.cr

class Document
  property name

  def initialize(@name : String)
  end

  def print
    puts "Hi, I'm printing #{@name}"
  end
end

class PDFDocument < Document
end

doc = ...