ruby/rails：如何确定是否包含模块？

Question

Expanding on my question here ( ruby/rails: extending or including other modules ), using my existing solution, what's the best way to determine if my module is included?

What I did for now was I defined instance methods on each module so when they get included a method would be available, and then I just added a catcher ( method_missing() ) to the parent module so I can catch if they are not included. My solution code looks like:

module Features
  FEATURES = [Running, Walking]

  # include Features::Running
  FEATURES.each do |feature|
    include feature
  end

  module ClassMethods
    # include Features::Running::ClassMethods
    FEATURES.each do |feature|
      include feature::ClassMethods
    end
  end

  module InstanceMethods
    def method_missing(meth)
      # Catch feature checks that are not included in models to return false
      if meth[-1] == '?' && meth.to_s =~ /can_(\w+)\z?/
        false
      else
        # You *must* call super if you don't handle the method,
        # otherwise you'll mess up Ruby's method lookup
        super
      end
    end
  end

  def self.included(base)
    base.send :extend, ClassMethods
    base.send :include, InstanceMethods
  end
end

# lib/features/running.rb
module Features::Running
  module ClassMethods
    def can_run
      ...

      # Define a method to have model know a way they have that feature
      define_method(:can_run?) { true }
    end
  end
end

# lib/features/walking.rb
module Features::Walking
  module ClassMethods
    def can_walk
      ...

      # Define a method to have model know a way they have that feature
      define_method(:can_walk?) { true }
    end
  end
end

So in my models I have:

# Sample models
class Man < ActiveRecord::Base
  # Include features modules
  include Features

  # Define what man can do
  can_walk
  can_run
end

class Car < ActiveRecord::Base
  # Include features modules
  include Features

  # Define what man can do
  can_run
end

And then I can

Man.new.can_walk?
# => true
Car.new.can_run?
# => true
Car.new.can_walk? # method_missing catches this
# => false

Did I write this correctly? Or is there a better way?

Answer 1

If I understand your question correctly, you can useModule#include? :

Man.include?(Features)

For example:

module M
end

class C
  include M
end

C.include?(M) # => true

Other ways

Checking Module#included_modules

This works, but it's a bit more indirect, since it generates intermediate included_modules array.

C.included_modules.include?(M) # => true

since C.included_modules has a value of [M, Kernel]

Checking Module#ancestors

C.ancestors.include?(M) #=> true

since C.ancestors has a value of [C, M, Object, Kernel, BasicObject]

Using operators like <

The Module class also declares several comparison operators:

• Module#<
• Module#<=
• Module#==
• Module#>=
• Module#>

Example:

C < M # => true