用pry阅读ruby源码--以task方法为例

曾经终败给现在 2022-08-21 02:16 178阅读 0赞

rails项目中有个目录 lib/tasks，里面定义了一个rake任务：

task hello: :hello do  
puts “hello”  
end

看到这里的时候，是不是可能会对 task 方法产生一些兴趣？

可以在rails项目的Gemfile中加入 pry这个强大的工具，然后一步步找到这个task方法的本质。

1，在task中加入断点：  
binding.pry

2，断点中用 show-method 方法  
用show-method按图索骥，可以层层揭开 task 的面纱。

[33] pry(main)> 
    [34] pry(main)> show-method task
    
    From: /home/liukun/.rvm/gems/ruby-2.1.1@zhe800_zhaoshang/gems/rake-10.0.4/lib/rake/dsl_definition.rb @ line 31:
    Owner: Rake::DSL
    Visibility: private
    Number of lines: 3
    
    def task(*args, &block)
      Rake::Task.define_task(*args, &block)
    end
    [35] pry(main)> show-method Rake::Task.define_task
    
    From: /home/liukun/.rvm/gems/ruby-2.1.1@zhe800_zhaoshang/gems/rake-10.0.4/lib/rake/task.rb @ line 350:
    Owner: #<Class:Rake::Task>
    Visibility: public
    Number of lines: 3
    
    def define_task(*args, &block)
      Rake.application.define_task(self, *args, &block)
    end
    [36] pry(main)> show-method Rake.application.define_task
    
    From: /home/liukun/.rvm/gems/ruby-2.1.1@zhe800_zhaoshang/gems/rake-10.0.4/lib/rake/task_manager.rb @ line 23:
    Owner: Rake::TaskManager
    Visibility: public
    Number of lines: 13
    
    def define_task(task_class, *args, &block)
      task_name, arg_names, deps = resolve_args(args)
      task_name = task_class.scope_name(@scope, task_name)
      deps = [deps] unless deps.respond_to?(:to_ary)
      deps = deps.collect {|d| d.to_s }
      task = intern(task_class, task_name)
      task.set_arg_names(arg_names) unless arg_names.empty?
      if Rake::TaskManager.record_task_metadata
        add_location(task)
        task.add_description(get_description(task))
      end
      task.enhance(deps, &block)
    end
    [37] pry(main)>

3， environment的作用是什么？  
用来通知Rake需要加载rails环境。  
参考：  
[http://stackoverflow.com/questions/7044714/whats-the-environment-task-in-rake][http_stackoverflow.com_questions_7044714_whats-the-environment-task-in-rake]

4，进一步理解 environment  
[http://jasonseifer.com/2010/04/06/rake-tutorial][http_jasonseifer.com_2010_04_06_rake-tutorial]

task :turn_off_alarm do
        puts "Turned off alarm. Would have liked 5 more minutes, though."
      end
    
      task :groom_myself do
        puts "Brushed teeth."
        puts "Showered."
        puts "Shaved."
      end
    
      task :make_coffee do
        cups = ENV["COFFEE_CUPS"] || 2
        puts "Made #{cups} cups of coffee. Shakes are gone."
      end
    
      task :walk_dog do
        puts "Dog walked."
      end
    
      task :ready_for_the_day => [:turn_off_alarm, :groom_myself, :make_coffee, :walk_dog] do
        puts "Ready for the day!"
      end

By running the ready\_for\_the\_day task it notices that the turn\_off\_alarm, groom\_myself, make\_coffee, and walk\_dog tasks are all prerequisites of the ready\_for\_the\_day task. Then it runs them all in the appropriate order.

[http_stackoverflow.com_questions_7044714_whats-the-environment-task-in-rake]: http://stackoverflow.com/questions/7044714/whats-the-environment-task-in-rake
[http_jasonseifer.com_2010_04_06_rake-tutorial]: http://jasonseifer.com/2010/04/06/rake-tutorial