ruby-on-rails - send() 方法的用途是什么？

Question

有人可以帮我理解下面列出的“send()”方法的用途吗？当我阅读下面的代码时，它的用途毫无意义。

这是一个 Rails 应用程序，使用 Ruby 1.8.7 和 Rails 1.2.3。请不要跟我唠叨升级，这是客户的环境，我没有那种闲暇。

不用说，我指的是这样的说法；

def do_schedule
  @performance = Performance.new(params[:performance])
  @performer = Performer.find(params[:performer_id])
  selected_track = params[:selected_track]
  if FileTest.exists?(File.expand_path(@performer.photo))
    @performance.photo = File.open(File.expand_path(@performer.photo))
  end

  @performance.audio = File.open(File.expand_path(@performer.send(selected_track)))

  if @performance.save
    flash[:notice] = 'Performer scheduled.'
    redirect_to :controller => :performer, :action => :index
  else
    render :action => 'schedule'
  end
end

表演者模型

class Performer < ActiveRecord::Base
  file_column :audio_one
  file_column :audio_two
  file_column :audio_three
  file_column :photo

  belongs_to :festival
  validates_presence_of :name, :first_name, :last_name, :address, :city, :state, :zip, :daytime_phone, :availability, :stages
  validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i
  validates_confirmation_of :email

  validates_presence_of :audio_one, :audio_two, :audio_three, :photo, :if => :submitted

  after_create :salt_access_key
  serialize :availability
  serialize :stages

  attr_accessor :other_type_of_music
  before_save :set_other_type

  def set_other_type
    if type_of_music == 'Other'
      self.type_of_music = "Other - #{other_type_of_music}" unless other_type_of_music.blank?
    end
  end

  def salt_access_key
    update_attribute(:access_key, Digest::SHA1.hexdigest("--#{self.id}--#{self.name}--#{self.festival.year}"))
  end

  def preferred_stages
    stages = []
    festival = Festival.find(self.festival_id.to_i)
    self.stages.collect { | key, value |
      id = key.gsub(/[\D]/, '').to_i
      if id > 0
        stages << festival.performance_stages.find(id).name
      end
    }
    return stages
  end
end

包含这个的 Controller 是Performance。我一直在谷歌上搜索，试图弄清楚“@performer.send(selected_track)”的实际用途，但我觉得自己正在与漩涡划桨。

Answer 1

用于向对象发送方法消息的 send 方法的 Ruby 实现是这样工作的:

class Car
  
  def start
    puts "vroom"
  end

  private

  def engine_temp
    puts "Just Right"
  end

end

@car = Car.new
@car.start # output: vroom
@car.send(:start) # output: vroom

这是基础知识，另外一条重要信息是 send 允许您将消息发送到 PRIVATE 方法，而不仅仅是公共(public)方法。

@car.engine_temp  # This doesn't work, it will raise an exception
@car.send(:engine_temp)  # output: Just Right

至于您的特定发送调用将做什么，很可能在 Performer 类中有一个 def method_missing 被设置为捕获它并执行一些操作。