class Aws::S3::PresignedPost

def self.define_field(field, *args)
  options = args.last.is_a?(Hash) ? args.pop : {}
  field_name = args.last || field.to_s
  define_method("#{field}") do |value|
    with(field_name, value)
  end
  if options[:starts_with]
    define_method("#{field}_starts_with") do |value|
      starts_with(field_name, value)
    end
  end
end