require 'json'

class Account
  def initialize(name, balance)
    @name = name
    @balance = balance
  end

  def to_h
    {
      name: @name,
      balance: @balance
    }
  end
end

vasya = Account.new("vasya", 100)
petya = Account.new("petya", 976)

accounts = [vasya, petya]

json = accounts.map(&:to_h).to_json

File.write("result.json", json + "\n")

> cat result.json
[{"name":"vasya","balance":100},{"name":"petya","balance":976}]

class Card
  def to_h
    {
      carrierName: carrierName
    }
  end
end


class AccauntsArray
  def to_h
    {
      nameAccaunt: nameAccaunt,
      currency: currency,
      availableBalance: availableBalance,
      classification: classification,
      array_card: array_card.map(&:to_h)
    }
  end
end

accounts.map(&:to_h).to_json