Return instances from class and build from_json

instances.cr

require "json"
 
struct Container
  include JSON::Serializable
  
  property a : Int32
  property b : String
  property c : String
  property d : String
  
  def initialize(@a, @b, @c, @d)
  end
  
  def self.build_instance
    self.new(a: 2, b: "b", c: "c", d: "d")
  end
end
 
p! Container.from_json(%({"a": 2, "b": "b", "c": "c", "d": "d"}))
p! Container.new(a: 2, b: "b", c: "c", d: "d")
p! Container.build_instance