Module: Dry::Monads::JSONCoder

Defined in:

lib/dry/monads/extensions/json.rb

Overview

Reads and writes monads as JSON via JSON::Coder.

This replaces the old json/add/dry/monads/maybe file, no longer working from json 3.0, which removed the whole json/add mechanism, so monads can no longer serialize via JSON.dump and JSON.load globally. A coder does the same job locally, without patching anything.

The wire format remains unchanged, so JSON written by older versions still loads.

Examples:

Dry::Monads.load_extensions(:json)

coder = Dry::Monads.json_coder
coder.dump(Some(3)) # => %({"json_class":"Dry::Monads::Maybe::Some","value":3})
coder.load(%({"json_class":"Dry::Monads::Maybe::Some","value":3})) # => Some(3)

Constant Summary

JSON_CLASS_KEY =

Key used to tag a serialized monad.

"json_class"

AS_JSON =

This constant is part of a private API. You should avoid using this constant if possible, as it may be removed or be changed in the future.

Called for every object the generator cannot write natively.

The second argument is true when the object is a hash key and false everywhere else. We do not use it, because a monad never appears as a key, but it must be accepted.

lambda { |object, *|
  case object
  when Maybe
    {JSON_CLASS_KEY => object.class.name, "value" => object.none? ? nil : object.value!}
  else
    object
  end
}

ON_LOAD =

This constant is part of a private API. You should avoid using this constant if possible, as it may be removed or be changed in the future.

Called for every value the parser produces, innermost first.

lambda { |value|
  next value unless value.is_a?(::Hash) && value.key?(JSON_CLASS_KEY)

  case value[JSON_CLASS_KEY]
  when Maybe::Some.name then Maybe::Some.new(value["value"])
  when Maybe::None.name then Maybe::None.instance
  else value
  end
}