Metaprograming

ruby-talk
1

i would like to know which methods are called by the object created by
class with in class.
If Suppose if particular method is not there it invokes
method_missing.But i want it invoke directly my class .so i would like
create that method dynamically
eg:
class Flower
def rose
puts "rose is beatiful"
end
end
f=flower.new
f.rose-------------------->It gives me rose
but now f.jasmine------------------->It calls method_missing
but i want it comes to my class "Flower"

So i Want to know which methods are invoked by my "Flower" object
Please help me

···

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

2

i would like to know which methods are called by the object created by
class with in class.
If Suppose if particular method is not there it invokes
method_missing.But i want it invoke directly my class .so i would like
create that method dynamically
eg:
class Flower
def rose
puts "rose is beatiful"
end
end
f=flower.new
f.rose-------------------->It gives me rose
but now f.jasmine------------------->It calls method_missing
but i want it comes to my class "Flower"

I'm not sure if I understand you correctly, but if you want those
method missing calls, to be called on the Flower class, you can do
this:

irb(main):001:0> class Flower
irb(main):002:1> def self.jasmine
irb(main):003:2> "jasmine"
irb(main):004:2> end
irb(main):005:1> def method_missing meth, *args, &blk
irb(main):006:2> self.class.send meth, *args, &blk
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):016:0> Flower.new.jasmine
=> "jasmine"

So i Want to know which methods are invoked by my "Flower" object

I don't understand this question.

Jesus.

···

On Thu, Jun 10, 2010 at 11:53 AM, Sateesh Kambhamapati <sateesh.mca09@gmail.com> wrote:

3

Jesús Gabriel y Galán wrote:

end
end
f=flower.new
f.rose-------------------->It gives me rose
but now f.jasmine------------------->It calls method_missing
but i want it comes to my class "Flower"

I'm not sure if I understand you correctly, but if you want those
method missing calls, to be called on the Flower class, you can do
this:

irb(main):001:0> class Flower
irb(main):002:1> def self.jasmine
irb(main):003:2> "jasmine"
irb(main):004:2> end
irb(main):005:1> def method_missing meth, *args, &blk
irb(main):006:2> self.class.send meth, *args, &blk
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):016:0> Flower.new.jasmine
=> "jasmine"

So i Want to know which methods are invoked by my "Flower" object

I don't understand this question.

Jesus.

Thanks for reply
i would like to know which methods are called by class object i.e
class Flower
     def jasmine
     puts "iam jasmine"
   end
      def rose
      puts "iam rose"
  end
end

flowerlist=Flower.new #----->Creating instance for flower
flowerlist.jasmine #------->"gives output as "iam jasmine"
flowerlist.rose # =======> "gives output as "i am rose"
flowerlist.lotus #------->"Shows No Method Error"

Question : --> My Question is i would like to know which methods are
called by object i.e flowerlist in the class Flower

if i already know those methods then
suppose if i have not define some method then i will define it
dynamically example here is "lotus"

i think u understand my question
pleasee gave me reply

···

On Thu, Jun 10, 2010 at 11:53 AM, Sateesh Kambhamapati > <sateesh.mca09@gmail.com> wrote:

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

4

I don't understand your question yet, but perhaps the following will
help. If this is not what you meant, please post exactly the code you
would like to write, and what results you would like from that code.

  module AutoMethodMaker
    def self.included(base)
      base.extend(ClassMethods)
    end
    def method_missing(method_name,*args)
      if self.class.maybe_make_method(method_name,*args)
        self.send(method_name,*args)
      end
    end
    module ClassMethods
      def methods_made
        @methods_made ||=
      end

      def auto_make_methods(pattern,&block)
        (@auto_make_methods ||= {})[ pattern ] = block
      end

      def maybe_make_method(method_name,*args)
        @auto_make_methods.each do |pattern,block|
          if pattern===method_name
            define_method(method_name,&block)
            methods_made << method_name
            return true
          end
        end
      end

    end
  end

  class Flower
    include AutoMethodMaker
    auto_make_methods /special_.+/ do
      puts "Special flower #{__method__[/special_(.+)/,1]}!!"
    end
    auto_make_methods /.+/ do
      puts "I am a #{__method__}"
    end
    def standard
      puts "I am a built-in method."
    end
  end

  f = Flower.new
  p Flower.methods_made #=>
  f.jasmine #=> I am a jasmine
  f.rose #=> I am a rose
  f.rose #=> I am a rose
  f.special_rose #=> Special flower rose!!
  f.standard #=> I am a built-in method.
  f.lotus #=> I am a lotus
  p Flower.methods_made #=> [:jasmine, :rose, :special_rose, :lotus]

···

On Jun 13, 11:23 pm, Sateesh Kambhamapati <sateesh.mc...@gmail.com> wrote:

>> So i Want to know which methods are invoked by my "Flower" object
> I don't understand this question.
flowerlist=Flower.new #----->Creating instance for flower
flowerlist.jasmine #------->"gives output as "iam jasmine"
flowerlist.rose # =======> "gives output as "i am rose"
flowerlist.lotus #------->"Shows No Method Error"

Question : --> My Question is i would like to know which methods are
called by object i.e flowerlist in the class Flower

if i already know those methods then
suppose if i have not define some method then i will define it
dynamically example here is "lotus"

i think u understand my question
pleasee gave me reply

5

Are you asking for the list of methods defined on the Object class? If so a simple 2 liner will give you the list of methods

obj = Object.new;
print obj.methods.sort.join("\n");

Raghu

···

On 14/06/10 10:53 AM, Sateesh Kambhamapati wrote:

Jesús Gabriel y Galán wrote:

On Thu, Jun 10, 2010 at 11:53 AM, Sateesh Kambhamapati >> <sateesh.mca09@gmail.com> wrote:

end
f=flower.new
f.rose-------------------->It gives me rose
but now f.jasmine------------------->It calls method_missing
but i want it comes to my class "Flower"

I'm not sure if I understand you correctly, but if you want those
method missing calls, to be called on the Flower class, you can do
this:

irb(main):001:0> class Flower
irb(main):002:1> def self.jasmine
irb(main):003:2> "jasmine"
irb(main):004:2> end
irb(main):005:1> def method_missing meth, *args,&blk
irb(main):006:2> self.class.send meth, *args,&blk
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):016:0> Flower.new.jasmine
=> "jasmine"

So i Want to know which methods are invoked by my "Flower" object

I don't understand this question.

Jesus.

Thanks for reply
i would like to know which methods are called by class object i.e
class Flower
      def jasmine
      puts "iam jasmine"
    end
       def rose
       puts "iam rose"
   end
end

flowerlist=Flower.new #----->Creating instance for flower
flowerlist.jasmine #------->"gives output as "iam jasmine"
flowerlist.rose # =======> "gives output as "i am rose"
flowerlist.lotus #------->"Shows No Method Error"

Question : --> My Question is i would like to know which methods are
called by object i.e flowerlist in the class Flower

if i already know those methods then
suppose if i have not define some method then i will define it
dynamically example here is "lotus"

i think u understand my question
pleasee gave me reply

6

As I understand the question now, I think the answer from Phrogz is
spot on. You need to use the method_missing method, which will catch
any call to a method you haven't defined:

class Flower
  def jasmine
    puts "iam jasmine"
  end
  def rose
    puts "iam rose"
  end

  def method_missing meth, *args, &blk
    puts "method #{meth} called, but not defined"
  end
end

flowerlist=Flower.new #----->Creating instance for flower
flowerlist.jasmine #------->"gives output as "iam jasmine"
flowerlist.rose # =======> "gives output as "i am rose"
flowerlist.lotus #=> "method lotus called, but not defined"

So, now you know where you have a place to do whatever you want to do
with a call to a method that doesn't exist. For example, if you want
to dynamically create a method that returns its name as a string, you
can do:

  def method_missing method, *args, &blk
    self.class.send(:define_method, method) do
      method.to_s
    end
    send(method)
  end

This will dynamically define (and call) a method that returns its name
as a string. So if you add that to the Flower class:

class Flower
  def method_missing method, *args, &blk
    self.class.send(:define_method, method) do
      method.to_s
    end
    send(method)
  end
end

f = Flower.new
f.lotus #=> "lotus"
f.rose #=> "rose"

and so on. In any case, I recommend looking at Phrogz's answer,
because it's a nice little utility to automatically define method that
do different things depending the the name patterns.

Regards,

Jesus.

···

On Mon, Jun 14, 2010 at 7:23 AM, Sateesh Kambhamapati <sateesh.mca09@gmail.com> wrote:

Jesús Gabriel y Galán wrote:

On Thu, Jun 10, 2010 at 11:53 AM, Sateesh Kambhamapati >> <sateesh.mca09@gmail.com> wrote:

end
end
f=flower.new
f.rose-------------------->It gives me rose
but now f.jasmine------------------->It calls method_missing
but i want it comes to my class "Flower"

I'm not sure if I understand you correctly, but if you want those
method missing calls, to be called on the Flower class, you can do
this:

irb(main):001:0> class Flower
irb(main):002:1> def self.jasmine
irb(main):003:2> "jasmine"
irb(main):004:2> end
irb(main):005:1> def method_missing meth, *args, &blk
irb(main):006:2> self.class.send meth, *args, &blk
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):016:0> Flower.new.jasmine
=> "jasmine"

So i Want to know which methods are invoked by my "Flower" object

I don't understand this question.

Jesus.

Thanks for reply
i would like to know which methods are called by class object i.e
class Flower
def jasmine
puts "iam jasmine"
end
def rose
puts "iam rose"
end
end

flowerlist=Flower.new #----->Creating instance for flower
flowerlist.jasmine #------->"gives output as "iam jasmine"
flowerlist.rose # =======> "gives output as "i am rose"
flowerlist.lotus #------->"Shows No Method Error"

Question : --> My Question is i would like to know which methods are
called by object i.e flowerlist in the class Flower

if i already know those methods then
suppose if i have not define some method then i will define it
dynamically example here is "lotus"

i think u understand my question

7

Sateesh Kambhamapati wrote:

i would like to know which methods are called by class object i.e

Not sure what you mean by "called by class object"

Question : --> My Question is i would like to know which methods are
called by object i.e flowerlist in the class Flower

if i already know those methods then
suppose if i have not define some method then i will define it
dynamically example here is "lotus"

If you want to intercept *all* calls to the object, then put a proxy
object in front of it, and delegate the calls (e.g. see
SimpleDelegator).

If you're happy to intercept only the unknown methods (which you will
then define), then method_missing is what you want.

class Flower
  def jasmine
    puts "I am jasmine"
  end
  def method_missing(meth,*args,&blk)
    puts "method #{meth.inspect} called with #{args.inspect}"
  end
end
flowerlist=Flower.new
flowerlist.jasmine # I am jasmine
flowerlist.lotus # method :lotus called with

···

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

8

My goodness. Has anyone asked why such metaprogramming might be necessary? I don't even understand the question, let enough to the extent that I would feel confident in suggesting such drastic measures as the solution.

Metaprogramming is not a universal hammer. Even if it were, you wouldn't want everything to be a nail.

···

On 2010-06-14 01:22:40 -0700, Jesús Gabriel y Galán said:

On Mon, Jun 14, 2010 at 7:23 AM, Sateesh Kambhamapati > <sateesh.mca09@gmail.com> wrote:

Jesús Gabriel y Galán wrote:

On Thu, Jun 10, 2010 at 11:53 AM, Sateesh Kambhamapati >>> <sateesh.mca09@gmail.com> wrote:

end
f=flower.new
f.rose-------------------->It gives me rose
but now f.jasmine------------------->It calls method_missing
but i want it comes to my class "Flower"

I'm not sure if I understand you correctly, but if you want those
method missing calls, to be called on the Flower class, you can do
this:

irb(main):001:0> class Flower
irb(main):002:1> def self.jasmine
irb(main):003:2> "jasmine"
irb(main):004:2> end
irb(main):005:1> def method_missing meth, *args, &blk
irb(main):006:2> self.class.send meth, *args, &blk
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):016:0> Flower.new.jasmine
=> "jasmine"

So i Want to know which methods are invoked by my "Flower" object

I don't understand this question.

Jesus.

Thanks for reply
i would like to know which methods are called by class object i.e
class Flower
def jasmine
puts "iam jasmine"
end
def rose
puts "iam rose"
end
end

flowerlist=Flower.new #----->Creating instance for flower
flowerlist.jasmine #------->"gives output as "iam jasmine"
flowerlist.rose # =======> "gives output as "i am rose"
flowerlist.lotus #------->"Shows No Method Error"

Question : --> My Question is i would like to know which methods are
called by object i.e flowerlist in the class Flower

if i already know those methods then
suppose if i have not define some method then i will define it
dynamically example here is "lotus"

i think u understand my question

As I understand the question now, I think the answer from Phrogz is
spot on. You need to use the method_missing method, which will catch
any call to a method you haven't defined:

class Flower
  def jasmine
    puts "iam jasmine"
  end
  def rose
    puts "iam rose"
  end

  def method_missing meth, *args, &blk
    puts "method #{meth} called, but not defined"
  end
end

flowerlist=Flower.new #----->Creating instance for flower
flowerlist.jasmine #------->"gives output as "iam jasmine"
flowerlist.rose # =======> "gives output as "i am rose"
flowerlist.lotus #=> "method lotus called, but not defined"

So, now you know where you have a place to do whatever you want to do
with a call to a method that doesn't exist. For example, if you want
to dynamically create a method that returns its name as a string, you
can do:

  def method_missing method, *args, &blk
    self.class.send(:define_method, method) do
      method.to_s
    end
    send(method)
  end

This will dynamically define (and call) a method that returns its name
as a string. So if you add that to the Flower class:

class Flower
  def method_missing method, *args, &blk
    self.class.send(:define_method, method) do
      method.to_s
    end
    send(method)
  end
end

f = Flower.new
f.lotus #=> "lotus"
f.rose #=> "rose"

and so on. In any case, I recommend looking at Phrogz's answer,
because it's a nice little utility to automatically define method that
do different things depending the the name patterns.

Regards,

Jesus.

--
Rein Henrichs

http://reinh.com

9

My goodness. Has anyone asked why such metaprogramming might be necessary? I
don't even understand the question, let enough to the extent that I would
feel confident in suggesting such drastic measures as the solution.

It's what I understood from the OP. He said:

"suppose if i have not define some method then i will define it dynamically"

From this and the rest of his question, I understood he wanted to
intercept calls to missing methods and define them dynamically.
Do you understand something different?

Metaprogramming is not a universal hammer. Even if it were, you wouldn't
want everything to be a nail.

I can agree with this, but when the OP explicitly asks for a way to
dynamically define missing methods, this is what comes to my mind.

Of course, it might very well be the case that to solve OP's problem,
this is not necessary at all and that studying his original problem
might lead to a different solution, but in any case I see no harm in
explaining him method_missing and how to define methods. Feel free to
ask him about what problem he is trying to solve, and maybe we can
come up with a better solution.

Regards,

Jesus.

···

On Mon, Jun 14, 2010 at 7:20 PM, Rein Henrichs <reinh@reinh.com> wrote:

10

Of course, it might very well be the case that to solve OP's problem,
this is not necessary at all and that studying his original problem
might lead to a different solution, but in any case I see no harm in
explaining him method_missing and how to define methods. Feel free to
ask him about what problem he is trying to solve, and maybe we can
come up with a better solution.

Regards,

Jesus.

Agreed. I would prefer that we attempt to understand a bit more of the context of the question.

Rant follows:

Questions like these are often the result of something like the Dunning–Kruger effect, where the questioner may not know enough to know that the question is bad and may only receive a confusing or misleading answer. For example:

···

On 2010-06-14 10:36:57 -0700, Jesús Gabriel y Galán said:

A: "How can I get more angular velocity out of this screwdriver?"

B: "Um, just twist it harder."

A: "Ok, that isn't helping me drive this nail in."

B: *facepalm* "Oh, you should be using a hammer."

TL;DR: Why does OP want to define methods dynamically? What business value would this provide?

--
Rein Henrichs

http://reinh.com

11

I agree, let's wait for him to answer about the original purpose of
his requirement. On the other hand, I think both things have value,
because there was clearly lack of knowledge that could be addressed,
and I think that providing that information could also help. Maybe, as
you say, not in this specific case, but to make the OP more
knowledgeable (sp?) about the language.

Jesus.

···

On Tue, Jun 15, 2010 at 1:21 AM, Rein Henrichs <reinh@reinh.com> wrote:

On 2010-06-14 10:36:57 -0700, Jesús Gabriel y Galán said:

Of course, it might very well be the case that to solve OP's problem,
this is not necessary at all and that studying his original problem
might lead to a different solution, but in any case I see no harm in
explaining him method_missing and how to define methods. Feel free to
ask him about what problem he is trying to solve, and maybe we can
come up with a better solution.

Regards,

Jesus.

Agreed. I would prefer that we attempt to understand a bit more of the
context of the question.

Rant follows:

Questions like these are often the result of something like the
Dunning–Kruger effect, where the questioner may not know enough to know that
the question is bad and may only receive a confusing or misleading answer.
For example:

A: "How can I get more angular velocity out of this screwdriver?"

B: "Um, just twist it harder."

A: "Ok, that isn't helping me drive this nail in."

B: *facepalm* "Oh, you should be using a hammer."

TL;DR: Why does OP want to define methods dynamically? What business value
would this provide?