Is there an easy way to extend an object?

ruby-talk
1

Given an object, is there a clean way of creating a new object that
wraps the original and then adds a new method?

It doesn't have to wrap the old object if there's a way to directly add
a new method to the object (I'm allowed to change the incoming object).

def extend_it(obj)

  # how do I add a method to obj
  # or create a wrapper for it?

  return obj #or new_obj that quacks like obj, has obj data, and also
has extra method

end

In my C++ days I would create a class that derives from the original
class, extends it with a new method, and defines a copy constructor to
copy the state of the original object.

Thanks
Jeff

···

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2

Hi --

Given an object, is there a clean way of creating a new object that
wraps the original and then adds a new method?

It doesn't have to wrap the old object if there's a way to directly add
a new method to the object (I'm allowed to change the incoming object).

def extend_it(obj)

# how do I add a method to obj
# or create a wrapper for it?

You can directly define a method on a particular object:

   def obj.new_method
     ...
   end

You can also create a module, and then use 'extend' to add that
module's instance method's to the object's capabilities.

   module M
     def x
     end
   end
   obj.extend(M)

There are a few more variants on these if they're not what you
need....

David

···

On Wed, 28 Dec 2005, Jeff Cohen wrote:

--
David A. Black
dblack@wobblini.net

"Ruby for Rails", from Manning Publications, coming April 2006!

3

Jeff.....

In a more-or-less "pure" OO language like Ruby (or Smalltalk), you don't have to go through all those gyrations that C++ (and other languages that added OO after the fact) forced us to use. You just add a method to the existing object because classes are first-class objects.

Cool, eh?

···

On Dec 27, 2005, at 5:40 PM, Jeff Cohen wrote:

Given an object, is there a clean way of creating a new object that
wraps the original and then adds a new method?

It doesn't have to wrap the old object if there's a way to directly add
a new method to the object (I'm allowed to change the incoming object).

def extend_it(obj)

  # how do I add a method to obj
  # or create a wrapper for it?

  return obj #or new_obj that quacks like obj, has obj data, and also
has extra method

end

In my C++ days I would create a class that derives from the original
class, extends it with a new method, and defines a copy constructor to
copy the state of the original object.

Thanks
Jeff

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

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Technology Visionary - Technology Assessment - Documentation
"Looking at technology from every angle"

4

unknown wrote:

You can directly define a method on a particular object:

   def obj.new_method
     ...
   end

That worked great! Thanks.

Jeff

···

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5

unknown wrote:

You can directly define a method on a particular object:

   def obj.new_method
     ...
   end

That worked great! Thanks.

Jeff

Just for the sake of completeness: if you are not allowed to modify the original instance or do not want to do it there's a delegator module:

require 'delegate'

=> true

s="foo"

=> "foo"

o=SimpleDelegater.new s

=> "foo"

o.length

=> 3

def o.foo() length * 2 end

=> nil

o.foo

=> 6

o << "bar"

=> "foobar"

o.length

=> 6

o.foo

=> 12

Kind regards

    robert

···

Jeff Cohen <cohen.jeff@gmail.com> wrote:

6

Robert Klemme wrote:

Just for the sake of completeness: if you are not allowed to modify the
original instance or do not want to do it there's a delegator module:

Now that is also really cool. Ruby is my first "dynamic" language and
I'm starting to see how powerful it can be.

Thanks for the tip.

Jeff

···

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