Question

我不确定Ruby中C风格回调的最佳习惯用语 - 或者是否有更好的东西（更像是C）。在C中，我会做类似的事情：

void DoStuff( int parameter, CallbackPtr callback )
{
  // Do stuff
  ...
  // Notify we're done
  callback( status_code )
}

什么是相当好的Ruby？基本上我想在“DoStuff”

中满足某个条件时调用传入的类方法

Answer 1

红宝石的等价物，不是惯用的，将是：

def my_callback(a, b, c, status_code)
  puts "did stuff with #{a}, #{b}, #{c} and got #{status_code}"
end

def do_stuff(a, b, c, callback)
  sum = a + b + c
  callback.call(a, b, c, sum)
end

def main
  a = 1
  b = 2
  c = 3
  do_stuff(a, b, c, method(:my_callback))
end

惯用法是传递一个块而不是一个方法的引用。块相对于独立方法的一个优点是上下文 - 块是closure，因此它可以引用声明它的范围中的变量。这减少了do_stuff需要传递给回调的参数数量。例如：

def do_stuff(a, b, c, &block)
  sum = a + b + c
  yield sum
end

def main
  a = 1
  b = 2
  c = 3
  do_stuff(a, b, c) { |status_code|
    puts "did stuff with #{a}, #{b}, #{c} and got #{status_code}"
  }
end

Answer 2

这个“惯用语块”是日常Ruby的核心部分，经常在书籍和教程中介绍。 Ruby information section提供了有用的[在线]学习资源的链接。

惯用的方法是使用一个块：

def x(z)
  yield z   # perhaps used in conjunction with #block_given?
end
x(3) {|y| y*y}  # => 9

或者可能转换为Proc;在这里，我展示了使用&block隐式转换为Proc的“块”，它只是另一个“可调用”值：

def x(z, &block)
  callback = block
  callback.call(z)
end

# look familiar?
x(4) {|y| y * y} # => 16

（仅使用上面的表格保存block-now-Proc以供以后使用或在其他特殊情况下使用，因为它会增加开销和语法噪音。）

然而，lambda可以很容易地使用（但这不是惯用的）：

def x(z,fn)
  fn.call(z)
end

# just use a lambda (closure)
x(5, lambda {|y| y * y}) # => 25

虽然上面的方法可以在创建闭包时包装“调用方法”，但绑定的Methods也可以被视为第一类可调用对象：

class A
  def b(z)
    z*z
  end
end

callable = A.new.method(:b)
callable.call(6) # => 36

# and since it's just a value...
def x(z,fn)
  fn.call(z)
end
x(7, callable) # => 49

此外，有时使用#send方法很有用（特别是如果名称已知方法）。这里它保存了一个在上一个例子中创建的中间Method对象; Ruby是一个消息传递系统：

# Using A from previous
def x(z, a):
  a.__send__(:b, z)
end
x(8, A.new) # => 64

快乐的编码！

Answer 3

更多地探讨了这个主题并更新了代码。

以下版本试图概括该技术，尽管仍然非常简化和不完整。

我在很大程度上偷了 - 下摆，发现了灵感 - 实现了DataMapper的回调，这在我看来非常完整和美丽。

我强烈建议您查看代码@ http://github.com/datamapper/dm-core/blob/master/lib/dm-core/support/hook.rb

无论如何，尝试使用Observable模块重现功能非常具有吸引力和启发性。几点说明：

添加的方法似乎是必需的，因为在注册回调时原始实例方法不可用
包括观察类和自我观察者
示例仅限于实例方法，不支持块，args等

代码：

require 'observer'

module SuperSimpleCallbacks
  include Observable

  def self.included(klass)
    klass.extend ClassMethods
    klass.initialize_included_features
  end

  # the observed is made also observer
  def initialize
    add_observer(self)
  end

  # TODO: dry
  def update(method_name, callback_type) # hook for the observer
    case callback_type
    when :before then self.class.callbacks[:before][method_name.to_sym].each{|callback| send callback}
    when :after then self.class.callbacks[:after][method_name.to_sym].each{|callback| send callback}
    end
  end

  module ClassMethods
    def initialize_included_features
      @callbacks = Hash.new
      @callbacks[:before] = Hash.new{|h,k| h[k] = []}
      @callbacks[:after] = @callbacks[:before].clone
      class << self
        attr_accessor :callbacks
      end
    end

    def method_added(method)
      redefine_method(method) if is_a_callback?(method)
    end

    def is_a_callback?(method)
      registered_methods.include?(method)
    end

    def registered_methods
      callbacks.values.map(&:keys).flatten.uniq
    end

    def store_callbacks(type, method_name, *callback_methods)
      callbacks[type.to_sym][method_name.to_sym] += callback_methods.flatten.map(&:to_sym)
    end

    def before(original_method, *callbacks)
      store_callbacks(:before, original_method, *callbacks)
    end

    def after(original_method, *callbacks)
      store_callbacks(:after, original_method, *callbacks)
    end

    def objectify_and_remove_method(method)
      if method_defined?(method.to_sym)
        original = instance_method(method.to_sym)
        remove_method(method.to_sym)
        original
      else
        nil
      end
    end

    def redefine_method(original_method)
      original = objectify_and_remove_method(original_method)
      mod = Module.new
      mod.class_eval do
        define_method(original_method.to_sym) do
          changed; notify_observers(original_method, :before)
          original.bind(self).call if original
          changed; notify_observers(original_method, :after)
        end
      end
      include mod
    end
  end
end


class MyObservedHouse
  include SuperSimpleCallbacks

  before :party, [:walk_dinosaure, :prepare, :just_idle]
  after :party, [:just_idle, :keep_house, :walk_dinosaure]

  before :home_office, [:just_idle, :prepare, :just_idle]
  after :home_office, [:just_idle, :walk_dinosaure, :just_idle]

  before :second_level, [:party]

  def home_office
    puts "learning and working with ruby...".upcase
  end

  def party
    puts "having party...".upcase
  end

  def just_idle
    puts "...."
  end

  def prepare
    puts "preparing snacks..."
  end

  def keep_house
    puts "house keeping..."
  end

  def walk_dinosaure
    puts "walking the dinosaure..."
  end

  def second_level
    puts "second level..."
  end
end

MyObservedHouse.new.tap do |house|
  puts "-------------------------"
  puts "-- about calling party --"
  puts "-------------------------"

  house.party

  puts "-------------------------------"
  puts "-- about calling home_office --"
  puts "-------------------------------"

  house.home_office

  puts "--------------------------------"
  puts "-- about calling second_level --"
  puts "--------------------------------"

  house.second_level
end
# => ...
# -------------------------
# -- about calling party --
# -------------------------
# walking the dinosaure...
# preparing snacks...
# ....
# HAVING PARTY...
# ....
# house keeping...
# walking the dinosaure...
# -------------------------------
# -- about calling home_office --
# -------------------------------
# ....
# preparing snacks...
# ....
# LEARNING AND WORKING WITH RUBY...
# ....
# walking the dinosaure...
# ....
# --------------------------------
# -- about calling second_level --
# --------------------------------
# walking the dinosaure...
# preparing snacks...
# ....
# HAVING PARTY...
# ....
# house keeping...
# walking the dinosaure...
# second level...

这个使用Observable的简单介绍可能很有用：http://www.oreillynet.com/ruby/blog/2006/01/ruby_design_patterns_observer.html

Answer 4

所以，这可能非常“非红宝石”，而且我不是一个“专业”的Ruby开发人员，所以如果你们要打成人，请温柔一点：）

Ruby有一个名为Observer的内置模块。我没有发现它易于使用，但公平地说我并没有给它太大的机会。在我的项目中，我使用了创建自己的EventHandler类型（是的，我经常使用C＃）。这是基本结构：

class EventHandler

  def initialize
    @client_map = {}
  end

  def add_listener(id, func)
    (@client_map[id.hash] ||= []) << func
  end

  def remove_listener(id)
    return @client_map.delete(id.hash)
  end

  def alert_listeners(*args)
    @client_map.each_value { |v| v.each { |func| func.call(*args) } }
  end

end

因此，为了使用它，我将它作为类的只读成员公开：

class Foo

  attr_reader :some_value_changed

  def initialize
    @some_value_changed = EventHandler.new
  end

end

“Foo”类的客户端可以订阅这样的事件：

foo.some_value_changed.add_listener(self, lambda { some_func })

我确信这不是惯用的Ruby，我只是将我的C＃体验转换为一种新语言，但它对我有用。

Answer 5

如果您愿意使用ActiveSupport（来自Rails），则可以轻松实现

class ObjectWithCallbackHooks
  include ActiveSupport::Callbacks
  define_callbacks :initialize # Your object supprots an :initialize callback chain

  include ObjectWithCallbackHooks::Plugin 

  def initialize(*)
    run_callbacks(:initialize) do # run `before` callbacks for :initialize
      puts "- initializing" # then run the content of the block
    end # then after_callbacks are ran
  end
end

module ObjectWithCallbackHooks::Plugin
  include ActiveSupport::Concern

  included do 
    # This plugin injects an "after_initialize" callback 
    set_callback :initialize, :after, :initialize_some_plugin
  end
end

Answer 6

我经常在Ruby中实现回调，如下例所示。使用起来非常舒服。

class Foo
   # Declare a callback.
   def initialize
     callback( :on_die_cast )
   end

   # Do some stuff.
   # The callback event :on_die_cast is triggered.
   # The variable "die" is passed to the callback block.
   def run
      while( true )
         die = 1 + rand( 6 )
         on_die_cast( die )
         sleep( die )
      end
   end

   # A method to define callback methods.
   # When the latter is called with a block, it's saved into a instance variable.
   # Else a saved code block is executed.
   def callback( *names )
      names.each do |name|
         eval <<-EOF
            @#{name} = false
            def #{name}( *args, &block )
               if( block )
                  @#{name} = block
               elsif( @#{name} )
                  @#{name}.call( *args )
               end
            end
         EOF
      end
   end
end

foo = Foo.new

# What should be done when the callback event is triggered?
foo.on_die_cast do |number|
   puts( number )
end

foo.run

Answer 7

我知道这是一篇旧帖子，但遇到这种情况的其他人可能会发现我的解决方案很有帮助。

http://chrisshepherddev.blogspot.com/2015/02/callbacks-in-pure-ruby-prepend-over.html

如何在Ruby中实现“回调”？

7 个答案: