require "json"

data = {
  "Mars"    => 1,
  "Jupyter" => 2,
  "Saturn"  => 3,
  "Earth"   => 4,
  "moons"   => ["Our", "Jupyters"],
  "missing" => nil,
}
puts data # Hash(String, Array(String) | Int32 | Nil)
json_string = data.to_json
puts json_string

parsed = JSON.parse(json_string)
puts parsed # JSON::Any

other = Hash(String, Array(String) | Int32 | Nil).from_json(json_string)
puts other.keys
