module BuildMaster
class Attribute
  def initialize(expression_evaluator)
    @evaluator = expression_evaluator
  end
  
  def process(target, template, source)
    name = template.attribute_value!('name')
    eval = template.attribute_value!('eval')
    if (not @evaluator.respond_to?(eval))
      raise TemplateError, '#{@evaluator.class} cannot evaluate expression #{eval}'
    end
    target.attributes[name] = @evaluator.send(eval, source.path)
  end
end
end