Metaprograming

Ruby
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

2

On Thu, Jun 10, 2010 at 11:53 AM, Sateesh K.
[email protected] 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.

3

Jesús Gabriel y Galán wrote:

On Thu, Jun 10, 2010 at 11:53 AM, Sateesh K.
[email protected] 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

4

On Jun 13, 11:23 pm, Sateesh K. [email protected]
wrote:

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

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]

5

Sateesh K. 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 []

6

On Mon, Jun 14, 2010 at 7:23 AM, Sateesh K.
[email protected] wrote:

I’m not sure if I understand you correctly, but if you want those
irb(main):008:1> end
Thanks for reply
flowerlist=Flower.new #----->Creating instance for flower

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.

7

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

but i want it comes to my class “Flower”
irb(main):006:2> self.class.send meth, *args, &blk
Jesus.
end
suppose if i have not define some method then i will define it
puts “iam jasmine”
flowerlist=Flower.new #----->Creating instance for flower
self.class.send(:define_method, method) do
self.class.send(:define_method, method) do
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.

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.

8

On 14/06/10 10:53 AM, Sateesh K. wrote:

I’m not sure if I understand you correctly, but if you want those
irb(main):008:1> end
Thanks for reply
flowerlist=Flower.new #----->Creating instance for flower

i think u understand my question
pleasee gave me reply

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

9

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?

10

On Mon, Jun 14, 2010 at 7:20 PM, Rein H. [email protected] wrote:

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.

11

On Tue, Jun 15, 2010 at 1:21 AM, Rein H. [email protected] wrote:

For example:
would this provide?
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.