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

[Chris Olsen]

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"

 

[Trans]

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. =A0Is there a way to ad= d
an include to an object instance rather than a class?

Thanks for the help

########
module SoftballStats
=A0 def to_sport
=A0 =A0 puts "softball"
=A0 end

=A0 def batting_average
=A0 =A0 0.563
=A0 end

=A0 def before_save
=A0 =A0 puts "in the softball before save"
=A0 end

end

module HockeyStats
=A0 def to_sport
=A0 =A0 puts "hockey"
=A0 end

=A0 def scoring_percentage
=A0 =A0 0.34
=A0 end

=A0 def before_save
=A0 =A0 puts "in the hockey before save"
=A0 end

end

class Stats

=A0 def self.create_by_sport(sport)
=A0 =A0 s =3D Stats.new
=A0 =A0 s.sport =3D sport
=A0 =A0 return s
=A0 end

=A0 def sport=3D(sport)
=A0 =A0 Stats.instance_eval do =A0# have tried to use self.instance_eval
=A0 =A0 =A0 eval("include #{sport.capitalize}Stats")
=A0 =A0 end
=A0 end

Couple of ways. One is to use the singleton.

def sport=3D(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.

 

[Chris Olsen]

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.

 

[Eric I.]

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.

 

[Tachikoma]

Hi Chris,


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.

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

 

[Chris Olsen]

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

I believe that will work for you.

That also works well.