Composing an attribute from multiple keys

Is it possible to create objects from multiple keys? For example, assuming I’m working with charges (payments) for a service and I’ve made a http request and received a hash like so:

  "charge": {
    "created_at":"2017-05-01 16:31:33 +0800",

I want to convert this into a Charge object with a Money object storing the amount and currency.

I can create the Money struct easily enough:

class Money < Dry::Struct
  attribute :amount, Types::Int
  attribute :currency, Types::String

I’d like to create a Charge object using something like:

response = http_get("http://...")
charge =, JSON.parse(response.body))

To do this I am using dry-initializer:

class Charge
  extend Dry::Initializer

  param :response, Types::Object
  option :created_at, Types::Json::DateTime

But I don’t know how to create an instance of Money from the amount and currency keys. I want to store the response object so that I can interrigate it if necessary (https status codes etc.).