Is there a way to call include for an object instance?

ruby-talk
1

I need to be able to create an object and, based on the param that I
pass in on the class create_for_sport method, create an object with the
proper module included.

It can be seen at the bottom by the comments I made that the includes
are being added on to the Stats class and the methods from the first
include are still there after the second include. Is there a way to add
an include to an object instance rather than a class?

Thanks for the help

···

########
module SoftballStats
  def to_sport
    puts "softball"
  end

  def batting_average
    0.563
  end

  def before_save
    puts "in the softball before save"
  end

end

module HockeyStats
  def to_sport
    puts "hockey"
  end

  def scoring_percentage
    0.34
  end

  def before_save
    puts "in the hockey before save"
  end

end

class Stats

  def self.create_by_sport(sport)
    s = Stats.new
    s.sport = sport
    return s
  end

  def sport=(sport)
    Stats.instance_eval do # have tried to use self.instance_eval
      eval("include #{sport.capitalize}Stats")
    end
  end

end

s = Stats.create_by_sport("softball")
puts s.batting_average # 0.563

h = Stats.create_by_sport("hockey")
puts h.scoring_percentage # 0.34
puts h.batting_average # 0.563 -> still has this method

s.before_save # "in the hockey save" -> softball before_save is now
overridden
h.before_save # "in the hockey save"
--
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2

Couple of ways. One is to use the singleton.

   def sport=(sport)
     (class << self; self; end).class_eval %{
       include #{sport.capitalize}Stats
     }
   end

But I think you might want to reconsider and use delegation instead.

T.

···

On Jul 15, 11:38 pm, Chris Olsen <olsen.ch...@gmail.com> wrote:

I need to be able to create an object and, based on the param that I
pass in on the class create_for_sport method, create an object with the
proper module included.

It can be seen at the bottom by the comments I made that the includes
are being added on to the Stats class and the methods from the first
include are still there after the second include. Is there a way to add
an include to an object instance rather than a class?

Thanks for the help

########
module SoftballStats
def to_sport
puts "softball"
end

def batting_average
0.563
end

def before_save
puts "in the softball before save"
end

end

module HockeyStats
def to_sport
puts "hockey"
end

def scoring_percentage
0.34
end

def before_save
puts "in the hockey before save"
end

end

class Stats

def self.create_by_sport(sport)
s = Stats.new
s.sport = sport
return s
end

def sport=(sport)
Stats.instance_eval do # have tried to use self.instance_eval
eval("include #{sport.capitalize}Stats")
end
end

3

Hi Chris,

I need to be able to create an object and, based on the param that I
pass in on the class create_for_sport method, create an object with the
proper module included.

You can call extend on an instance to mix in a modules instance
methods to the instance (and leaving the class itself alone). In your
code, we also need to convert your string to a reference to the module
as well, via a call to const_get. And this would be your new sport=
method:

  def sport=(sport)
    extend(self.class.const_get(sport.capitalize + "Stats"))
  end

I believe that will work for you.

Eric

···

====

LearnRuby.com offers Rails & Ruby HANDS-ON public & ON-SITE workshops.
Please visit http://LearnRuby.com for all the details.

4

Trans wrote:

···

On Jul 15, 11:38�pm, Chris Olsen <olsen.ch...@gmail.com> wrote:

� def before_save
� def scoring_percentage

� end

Couple of ways. One is to use the singleton.

   def sport=(sport)
     (class << self; self; end).class_eval %{
       include #{sport.capitalize}Stats
     }
   end

But I think you might want to reconsider and use delegation instead.

T.

Thanks so much. To be honest I have no idea what the (class << self;
self; end), but it will make for good reading :). I will look into the
delegation as well.

Thanks again.
--
Posted via http://www.ruby-forum.com/\.

5

you should put module(s) into class ,to ensure class Stats has the
permission of module,so try following code

class Stats
  module HockeyStats
    def to_sport
      puts "hockey"
    end

    def scoring_percentage
      0.34
    end

    def before_save
      puts "in the hockey before save"
    end

  end

  module SoftballStats
      def to_sport
        puts "softball"
      end

      def batting_average
        0.563
      end

      def before_save
        puts "in the softball before save"
      end

  end

  def self.create_by_sport(sport)
    s = Stats.new
    s.sport = sport
    return s
  end

  def sport=(sport)
    eval "extend #{sport.to_s.capitalize}Stats"
  end

end

···

On Jul 16, 12:11 pm, "Eric I." <rubytrain...@gmail.com> wrote:

Hi Chris,

> I need to be able to create an object and, based on the param that I
> pass in on the class create_for_sport method, create an object with the
> proper module included.

You can call extend on an instance to mix in a modules instance
methods to the instance (and leaving the class itself alone). In your
code, we also need to convert your string to a reference to the module
as well, via a call to const_get. And this would be your new sport=
method:

def sport=(sport)
extend(self.class.const_get(sport.capitalize + "Stats"))
end

I believe that will work for you.

Eric

====

LearnRuby.com offers Rails & Ruby HANDS-ON public & ON-SITE workshops.
Please visithttp://LearnRuby.comfor all the details.

6

Eric I. wrote:

  def sport=(sport)
    extend(self.class.const_get(sport.capitalize + "Stats"))
  end

I believe that will work for you.

That also works well.

···

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