Question

我的第一个想法是这样的事情：

class AbstractBuilder
  attr_reader :time_taken

  def build_with_timer
    started_at = Time.now
    build
    @time_taken = Time.now - started_at
  end

  def build
    raise 'Implement this method in a subclass' 
  end
end

class MyBuilder < AbstractBuilder
  def build
    sleep(5)
  end
end

builder = MyBuilder.new.build_with_timer
puts builder.time_taken

我怀疑有更好的方法可以提供更好的灵活性，例如理想情况下我想在MyBuilder的实例上调用'build'而不是'build_with_timer'，并且总是记录执行时间。

我确实考虑过使用初始化的alias_method，甚至使用模块mixin而不是类继承，它会覆盖在中间调用super的构建方法（不确定是否可行）。在我走下兔子洞之前，我想我会看看是否有既定的做法。

Answer 1

我对一个版本进行了攻击以达到你想要的效果。此版本不要求子类具有任何额外的代码。

class AbstractBuilder

  @@disable_override = false

  def before_method
    puts "before"
  end

  def after_method
    puts "after"
  end

  def self.method_added name
    unless @@disable_override
      if name == :build
        @@disable_override = true # to stop the new build method 
        self.send :alias_method, :sub_build, :build
        self.send :remove_method, :build
        self.send :define_method, :build do
          before_method
          sub_build
          after_method
        end
        @@disable_override = false
      else
        puts "defining other method #{name}"
      end
    end
  end

end

class MyBuilder < AbstractBuilder

  def build
    puts "starting build"
    sleep(5)
    puts "built."
  end

  def unnaffected_method
    # this method won't get redefined
  end

end

b = MyBuilder.new
b.build

输出

defining other method unnaffected_method
before
starting build
built.
after

Answer 2

我会玩alias_method：

module Timeable
  def time_methods *meths
    meths.each do |meth|
      alias_method "old_#{meth}", meth

      define_method meth do |*args|
        started_at = Time.now
        res = send "old_#{meth}", *args
        puts "Execution took %f seconds" % (Time.now - started_at)
        res
      end
    end
  end

end

class Foo
  def bar str
    puts str
  end
end

Foo.extend Timeable
Foo.time_methods :bar
Foo.new.bar('asd')
#=>asd
#=>Execution took 0.000050 seconds

Answer 3

听起来你正在寻找对象生命周期事件的钩子。你必须将它构建到你的基础对象中并提供一点DSL - 我认为你是在追求ActiveRecord Callbacks之类的东西。以下是我们如何修改您的示例以允许类似的内容：

class AbstractBuilder
  attr_reader :time_taken

  def construct! # i.e., build, and also call your hooks
    @@prebuild.each { |sym| self.send(sym) }
    build
    @@postbuild.each { |sym| self.send(sym) }
  end  

  def construct_with_timer
    started_at = Time.now
    construct!
    @time_taken = Time.now - started_at

    puts "!!! Build time: #@time_taken"
  end

  class << self
    def before_build(fn); @@prebuild ||= []; @@prebuild << fn; end
    def after_build(fn);  @@postbuild ||= []; @@postbuild << fn; end
  end
end

class MyBuilder < AbstractBuilder
  before_build :preprocess
  after_build  :postprocess

  def build; puts "BUILDING"; sleep(3); end
  def preprocess;  puts "Preparing to build..."; end
  def postprocess; puts "Done building. Thank you for waiting."; end
end

builder = MyBuilder.new
builder.construct_with_timer

# => Preparing to build...
# => BUILDING
# => Done building. Thank you for waiting.
# => !!! Build time: 3.000119

Answer 4

这是Aspect-Oriented Programming的教科书定义用例。它通常提供更清晰的关注点分离。在这个领域，Ruby提供Aquarium和AspectR。但是，您可能不希望向项目添加其他依赖项。因此，您可能仍会考虑使用其他方法之一。

如何在子类中的方法之前和之后运行代码？

4 个答案: