How can I choose which version of a module to include dynamically in Ruby?

Question

I\'m writing a small Ruby command-line application that uses fileutils from the standard library for file operations. Depending on how the user invokes the applicat

Answer 1

So what if it's private?

class Worker
  def initialize(verbose=false)
    if verbose
      (class <<self; include FileUtils::Verbose; end)
    else
      (class <<self; include FileUtils; end)
    end
    touch "test"
  end
end

This includes FileUtils::something in particular's Worker's metaclass - not in the main Worker class. Different workers can use different FileUtils this way.

Answer 2

If you would like to avoid the "switch" and inject the module, the

def initialize(injected_module)
    class << self
        include injected_module
    end
end

syntax won't work (the injected_module variable is out of scope). You could use the self.class.send trick, but per object instance extending seems more reasonable to me, not only because it is shorter to write:

def initialize(injected_module = MyDefaultModule)
    extend injected_module
end

but also it minimizes the side effects - the shared and easily changable state of the class, which can result in an unexpected behavior in a larger project. In Ruby the is no real "privacy" so to say, but some methods are marked private not without a reason.

Answer 3

Conditionally including the module through the send methods works for me as in the below tested example:

class Artefact
  include HPALMGenericApi
  # the initializer just sets the server name we will be using ans also the 'transport' method : Rest or OTA (set in the opt parameter)
  def initialize server, opt = {}  
    # conditionally include the Rest or OTA module
    self.class.send(:include, HPALMApiRest) if (opt.empty? || (opt && opt[:using] opt[:using] == :Rest)) 
    self.class.send(:include, HPALMApiOTA) if (opt && opt[:using] opt[:using] == :OTA)    
    # ... rest of initialization code  
  end
end