class Symbol

Symbol.json_create(x) # => :foo

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

# => {"json_class"=>"Symbol", "s"=>"foo"}
x = :foo.as_json
require 'json/add/symbol'

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

see Marshal[https://docs.ruby-lang.org/en/master/Marshal.html].
to serialize and deserialize a \Symbol object;
Methods Symbol#as_json and +Symbol.json_create+ may be used

def as_json(*)
  {
    JSON.create_id => self.class.name,
    's'            => to_s,
  }
end