JSON.#parse

require "json"

JSON.parse('[1,2,{"name":"tanaka","age":19}]')
# => [1, 2, {"name"=>"tanaka", "age"=>19}]

JSON.#generate

require "json"

JSON.generate([1, 2, { name: "tanaka", age: 19 }])
# => "[1,2,{\"name\":\"tanaka\",\"age\":19}]"

to_json, as_json

module JSON (Ruby 3.0.0 リファレンスマニュアル)

require "json"

class User
  attr :id, :name
  def initialize(id, name)
    @id, @name = id, name
  end

  def self.json_create(object)
    new(object['id'], object["name"])
  end

  def as_json(*)
    {
      JSON.create_id => self.class.name,
      "id" => id,
      "name" => name,
    }
  end

  def to_json(*)
    as_json.to_json
  end
end

json = JSON.generate(User.new(1, "tanaka"))
json # => "{\"json_class\":\"User\",\"id\":1,\"name\":\"tanaka\"}"
JSON.parse(json, create_additions: true)
# => #<User:0x0000557709b269e0 @id=1, @name="tanaka">

> JSON.create_id
=> "json_class"