class DateTime

def as_json(*)


DateTime.json_create(x) # BUG? Raises Date::Error "invalid date"

\Method +JSON.create+ deserializes such a hash, returning a \DateTime object:

# => {"json_class"=>"DateTime", "y"=>2023, "m"=>11, "d"=>21, "sg"=>2299161.0}
x = DateTime.now.as_json
require 'json/add/datetime'

returning a 2-element hash representing +self+:
\Method DateTime#as_json serializes +self+,

see Marshal[https://docs.ruby-lang.org/en/master/Marshal.html].
to serialize and deserialize a \DateTime object;
Methods DateTime#as_json and +DateTime.json_create+ may be used
def as_json(*)
  {
    JSON.create_id => self.class.name,
    'y' => year,
    'm' => month,
    'd' => day,
    'H' => hour,
    'M' => min,
    'S' => sec,
    'of' => offset.to_s,
    'sg' => start,
  }
end