Ruby class << self 元编程问题
User Model:
class User < ActiveRecord::Base
has_one :profile, :dependent => :destroy
delegate :gender, :to => :profile, :prefix=> false, :allow_nil => true
delegate :bio, :to => :profile, :prefix=> false, :allow_nil => true
... ...
end
问题来了，如果 profile 里有很多方法我想通过 delegate 这样加到 user 中来，要写很多 delegate...造轮子了
看到过有人写过这样的代码
class Post < ActiveRecord::Base
STATUSES = ['draft', 'published', 'spam']
validate_inclusion_of :status, :in => STATUSES
class <<self
STATUSES.each do |status_name|
define_method "all_#{status_name}" do
find(:all, :conditions => { :status => status_name }
end
end
end
end
想请教下，怎么通过这种方法解决写多个 delegate 的问题
delegate :gender, :bio, :a, :b, :c, :to => :profile, :prefix=> false, :allow_nil => true
从楼主的标题看来楼主不懂元编程 不懂元编程的人写出来的元编程往往更难维护... 建议楼主或者先把 Ruby 基础语法和先研究明白，或者系统学习一下元编程，或者干脆直接写几个 delegate
其实几次 delegate 虽然不 DRY，但是几乎木有什么额外的维护成本....
如果真的很多，可以 Extract model code to Module.去看看 ihower 的 slide 啦:-)
def delegate(*methods)
options = methods.pop
unless options.is_a?(Hash) && to = options[:to]
raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate :hello, :to => :greeter)."
end
if options[:prefix] == true && options[:to].to_s =~ /^[^a-z_]/
raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
end
prefix = options[:prefix] && "#{options[:prefix] == true ? to : options[:prefix]}_"
methods.each do |method|
module_eval(<<-EOS, "(__DELEGATION__)", 1)
def #{prefix}#{method}(*args, &block)
#{to}.__send__(#{method.inspect}, *args, &block)
end
EOS
end
end
看了源码就知道怎么写了吧
