Calling binding() within a module method (for mixin)?

ruby-talk
1

I've been trying to write a method that can dynamically mixin a module
to a class. I tried the following code:

···

#=========================================
module MixinUtils
def MixinUtils.includeMixin(className,mixinName,vars)
  evalStr= <<-END
    class #{className.to_s}
      include #{mixinName.to_s}
    end
  END
  eval(evalStr, vars)
end
end

module Foo
  def printFoo
    puts "foo"
  end
end

class Array
  def someMethod
    self.each do |item|
      MixinUtils.includeMixin(item.class.to_s,"Foo",binding)
      item.printFoo
    end
  end
end

[1,2,3].someMethod
#======================================

But running this gives

question.rb:22:in `something': undefined method `printFoo' for
1:Fixnum (NoMethodError)
        from question.rb:20:in `each'
        from question.rb:20:in `something'
        from question.rb:31

But if I take out the '[1,nil,true].something' and append

a=1
MixinUtils.includeMixin("Fixnum","Foo",binding)
a.printFoo

it produces

foo

as expected. Why the difference? Why does calling 'binding' inside a
block produce different results? Thanks in advance...

Ben

2

  eval(evalStr, vars)

eval is evil

end

write it like this

      MixinUtils.includeMixin(item.class.to_s,"Foo",binding)
      item.printFoo

                        Array::Fixnum.new.printFoo

    end

Guy Decoux

3

Ben schrieb:

I've been trying to write a method that can dynamically mixin a module
to a class. I tried the following code:

> (... code using eval ...)

Hi Ben,

in order to avoid eval as Guy suggested, you could try

   module MixinUtils
     def self.includeMixin(klass, mixin)
       klass.send(:include, mixin) # include is a private method
     end
   end

   module Foo
     def printFoo
       puts "foo"
     end
   end

   class Array
     def someMethod
       self.each do |item|
         MixinUtils.includeMixin(item.class, Foo)
         item.printFoo
       end
     end
   end

Calling

   [1,nil,true].someMethod

results in

   foo

as you expected.

Regards,
Pit

4

Pit Capitain <pit@capitain.de> wrote in message news:<418E0C85.3050502@capitain.de>...

Ben schrieb:
> I've been trying to write a method that can dynamically mixin a module
> to a class. I tried the following code:
> (... code using eval ...)

Hi Ben,

in order to avoid eval as Guy suggested, you could try

   module MixinUtils
     def self.includeMixin(klass, mixin)
       klass.send(:include, mixin) # include is a private method
     end
   end

   module Foo
     def printFoo
       puts "foo"
     end
   end

   class Array
     def someMethod
       self.each do |item|
         MixinUtils.includeMixin(item.class, Foo)
         item.printFoo
       end
     end
   end

Calling

   [1,nil,true].someMethod

results in

   foo
   foo
   foo

as you expected.

Regards,
Pit

I'll try this out. Thanks!