A union between multiple types, distinguished with a tag or by attempting to validate.

Constraints

• :storage - How the value will be stored when persisted.
  :type_and_value will store the type and value in a map like so {type: :type_name, value: the_value} :map_with_tag will store the value directly. This only works if all types have a tag and tag_value configured. Valid values are :type_and_value, :map_with_tag The default value is :type_and_value.

• :types - The types to be unioned, a map of an identifier for the enum value to its configuration.
  When using tag and tag_value we are referring to a map key that must equal a certain value in order for the value to be considered an instance of that type.
  For example:

  types:  [
    int: [
      type: :integer,
      constraints: [
        max: 10
      ]
    ],
    object: [
      type: MyObjectType,
      # The default value is `true`
      # this passes the tag key/value to the nested type
      # when casting input
      cast_tag?: true,
      tag: :type,
      tag_value: "my_object"
    ],
    other_object: [
      type: MyOtherObjectType,
      cast_tag?: true,
      tag: :type,
      tag_value: "my_other_object"
    ],
    other_object_without_type: [
      type: MyOtherObjectTypeWithoutType,
      cast_tag?: false,
      tag: :type,
      tag_value: nil
    ]
  ]  

  IMPORTANT:
  This is stored as a map under the hood. Filters over the data will need to take this into account.
  Additionally, if you are not using a tag, a value will be considered to be of the given type if it successfully casts. This means that, for example, if you try to cast "10" as a union of a string and an integer, it will end up as "10" because it is a string. If you put the integer type ahead of the string type, it will cast first and 10 will be the value.