simple_form_array_input.rb
class ArrayInput < SimpleForm::Inputs::StringInput
def input
input_html_options[:type] ||= input_type
existing_values = Array(object.public_send(attribute_name)).map do |element|
@builder.text_field(nil, input_html_options.merge(value: element, name: "#{object_name}[#{attribute_name}][]"))
end