Programming Crystal

Structuring a Class

In the previous section, and in ​Organizing Code in Classes and Modules​, you saw a simple Mineral class. Here’s the class code by itself without any additional logic:

class Mineral
  getter name : String
  getter hardness : Float64
  getter crystal_struct : String

  def initialize(@name, @hardness, @crystal_struct)  # constructor
  end
end

This class has three read-only instance variables: name, hardness, and crystal_struct. Giving them a type is imposed by the Crystal compiler. But you can also do this in the initialize method:

classes_and_structs/classes.cr

class Mineral
  getter name, hardness, crystal_struct

  def initialize(@name : String,
                 @hardness : Float64,
                 @crystal_struct : String)