产量<<自在类方法 [英] Yield in class &lt;&lt; self in class method

问题描述

我想创建一个类方法，它接受一个方法定义块并将其注入到类中.现在，self 确实是 Tom 对象，所以 class <<self 确实打开了它，但是 yield 似乎不起作用.我的理论知识不是那么深，所以我不确定为什么这不起作用.我可能完全错了，所以请随时讨论替代方案.

I want to create a class method that takes a block of method definitions and injects it into the class. Now, self is indeed the Tom object so class << self does open it up, but yield doesn't seem to work. My theoretical knowledge is not that deep, so I am not sure why this is not working. I might be getting this totally wrong, so feel free to discuss alternatives.

class Tom < Person
  mega_methods do
    def hiya!
      puts 'hiYA!'
    end
  end
end

class Person
  def self.mega_methods
    ...
    class << self
      yield
    end
  end
end

Tom.hiya!

我知道我可以使用 class << 在 Tom 中定义方法.self 或者我可以包含 class <<self 在块中.

I am aware I could just define the methods in Tom using class << self or that I could include class << self in the block.

我也想出了这个替代方案:

I also figured out this alternative:

def self.mega_methods &block
  if block_given?
    extension =  Module.new(&Proc.new)
    self.extend(extension)
  end
end

这个问题更多的是帮助我理解 Ruby 的工作原理，而不是解决一个特定的问题.

This question is more about helping me understand the workings of Ruby rather than solving a specific issue.

推荐答案

这有点奇怪，但如果您正在探索 Ruby，那就没问题了.

It's a little bit weird, but OK if you are exploring Ruby.

class Person
  puts "evaluating Person's body ..."
  def self.mega_methods
      puts 'in Person#self.mega_methods, about to yield ...'
      yield
  end
end

class Tom < Person
  puts "evaluating Tom's body ..."
  print 'Tom.singleton_methods : '; p Tom.singleton_methods
  mega_methods do
    puts 'in Tom, about to define self.hiya!'
    def self.hiya!
      puts 'hiYA!'
    end
  end
  print 'Tom.singleton_methods : '; p Tom.singleton_methods
end

Tom.hiya!

执行:

$ ruby -w t.rb 
evaluating Person's body ...
evaluating Tom's body ...
Tom.singleton_methods : ["mega_methods"]
in Person#self.mega_methods, about to yield ...
in Tom, about to define self.hiya!
Tom.singleton_methods : ["mega_methods", "hiya!"]
hiYA!

请注意，按照惯例，方法名称中的感叹号是为销毁方法保留的，例如修改接收者字符串的 String#sub!.

Note that the exclamation point in the name of a method is, by convention, reserved for destroying methods, such as String#sub! which modifies the receiver string.

另见 什么是 def `self.function` 名称是什么意思?

一切都是为了自己！

class Person2
  def self.mega_methods
    print 'in Person2 self='; p self
    class << self
      print 'in class << self self='; p self
      yield
    end
  end
end

class Tom2 < Person2
  mega_methods do
    puts "in Tom2, about to define self.hiya! for self=#{self}"
    def self.hiya!
      puts 'hiYA!'
    end
    def hi
      puts 'hi'
    end
  end
end

print 'Tom2.singleton_methods : '; p Tom2.singleton_methods
print 'Tom2.instance_methods  : '; p Tom2.instance_methods(false)
Tom2.hiya!
Tom2.new.hi

执行:

$ ruby -w t2.rb 
in Person2 self=Tom2
in class << self self=#<Class:Tom2>
in Tom2, about to define self.hiya! for self=Tom2
Tom2.singleton_methods : ["mega_methods", "hiya!"]
Tom2.instance_methods  : ["hi"]
hiYA!
hi

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