如何声明一个mixin方法,使它可以从实例方法和类方法中使用？

Question

我想在Ruby模块中放置一个方法,以便可以使用简单的语法从类方法或实例方法调用它:

module MyMod
  def fmt *args
    args.map { | a | "You said #{a}" }
  end
end

class MyClass
  include MyMod
  def inst
    puts fmt 1,2,3
  end
  def self.cls
    puts fmt 4,5,6
  end
end

上面的方法不起作用,因为类method(cls)无法看到实例方法fmt.如果我将定义更改为self.fmt,则实例方法必须将其作为调用MyMod.fmt.

我希望能够fmt (some stuff)从这两种方法中调用.这样做有"ruby-ish"方式吗？我可以将模块定义为

module MyMod
  def self.fmt *args
    args.map { | a | "You said #{a}" }
  end
  def fmt *args
    MyMod.fmt args
  end
end

但那不是很干,是吗？有更简单的方法吗？

Answer 1

你可以利用Module#included方法来做到这一点:

module MyMod
  # here base is a class the module is included into
  def self.included(base)
    # extend includes all methods of the module as class methods
    # into the target class
    base.extend self
  end

  def fmt(*args)
    args.map { |a| "You said #{a}" }
  end
end

class MyClass
  # regular include provides us with instance methods
  # and defined above MyMod#included hook - with class methods
  include MyMod

  def inst
    puts fmt(1, 2, 3)
  end

  def self.cls
    puts fmt(4, 5, 6)
  end
end

puts MyClass.cls
puts MyClass.new.inst

这是输出:

You said 4
You said 5
You said 6

You said 1
You said 2
You said 3

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