class Template
        def initialize(data)
            @data = StringIO.new(data)
            @params = {}
            yield self if block_given?
        end

        def add_param(key, value)
            @params.merge!({key => value})
        end

        def generate
            @params.each do |k,v|
                instance_variable_set :"@#{k}", v
            end
            ERB.new(@data.read).result(binding)
        end
    end
end


# rspec:

describe Template do

        it 'test' do
            template = Template.new('data: <%= var_1 %>, <%= var_2 %>, <%= var_3 %>') do |template|
                template.add_param :var_1, 'val-1'
                template.add_param :var_2, 'val-2'
                template.add_param :var_3, 'val-3'
            end
            pp template.generate
        end
    end