# Query

**URL:** <https://www.ruby-forum.com/t/query/172753>\
**Category:** Ruby\
**Created:** [July 27, 2009, 3:00pm UTC](https://www.ruby-forum.com/t/query/172753 "2009-07-27T15:00:34Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![hunt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/71e660/32.png) [@hunt](https://www.ruby-forum.com/u/hunt)\
**Post date:** [July 27, 2009, 3:00pm UTC](https://www.ruby-forum.com/t/query/172753/1 "2009-07-27T15:00:34Z")

</div>

hi friends,

I hav a query to ask…

class A  
def self.go  
return A.new  
end

def method\_missing( method\_name)  
puts in methodmissing  
puts " #{method\_name} method is missing"  
end

end

a = A.go  
a.name # a.name will print in method missing & name method is missing.

upto here it is working.

now when i create an object

A.new.add # it also prints in method missing & add method is missing.

which i don’t want I want that class method go which return an instance  
should call method\_missing not an instance which is created  
by A.new

how am i supposed to do?

---

<div class="post-metadata">

**Author:** ![hunt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/71e660/32.png) [@hunt](https://www.ruby-forum.com/u/hunt)\
**Post date:** [July 27, 2009, 3:31pm UTC](https://www.ruby-forum.com/t/query/172753/2 "2009-07-27T15:31:06Z")

</div>

hi, try this:

class A  
class \<\< self  
def go  
obj = A.new  
def obj.method\_missing \*args  
p ‘method missing’  
end  
obj  
end  
end  
end

A.go.uiae  
A.new.uiae

Greetz!

---

<div class="post-metadata">

**Author:** ![hunt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/71e660/32.png) [@hunt](https://www.ruby-forum.com/u/hunt)\
**Post date:** [July 27, 2009, 3:31pm UTC](https://www.ruby-forum.com/t/query/172753/3 "2009-07-27T15:31:22Z")

</div>

Hunt H. wrote:

> class A  
> def self.go  
> return A.new  
> end
> 
> def method\_missing( method\_name)  
> puts in methodmissing  
> puts " #{method\_name} method is missing"  
> end
> 
> end

You’re missing the quotes around the first puts:

puts “in method\_missing”

but otherwise that’s fine.

> now when i create an object
> 
> A.new.add # it also prints in method missing & add method is missing.

Of course. A.new creates a new instance of A. This new object doesn’t  
have any instance methods of its own (except those which it inherits  
from Object), so calling A.new.anything will trigger the method\_missing  
hook.

> which i don’t want I want that class method go which return an instance  
> should call method\_missing not an instance which is created  
> by A.new

I’m not sure what you mean - can you give a more concrete example? Your  
class method A.go calls A.new internally, so there is obviously no  
difference between an object created by A.go and one created by A.new.

Do you want to prevent a user from calling A.new? You can do

class A  
class \<\< self  
protected :new  
end  
end

But in Ruby, you can never prevent anything 100%. There are many  
different ways a user could call A.new bypassing this restriction (e.g.  
using class\_eval or send)

Otherwise, if you want an object returned by A.go to behave differently  
to an object returned by A.new, then you will have to make them  
different somehow. For example:

- A.go returns an object of a different class
- A.go returns an object with instance variables set differently
- A.go returns an object with singleton methods

An example of the third case:

class A  
def A.go  
res = A.new  
def res.method\_missing(\*args)  
puts “method\_missing: #{args.inspect}”  
end  
res  
end  
end  
A.go.wibble # has method\_missing method  
A.new.wibble # doesn’t

This can be done in a cleaner, more extendable way:

class A  
module GoMethods  
def method\_missing(\*args)  
puts “method\_missing: #{args.inspect}”  
end  
end  
def A.go  
A.new.extend GoMethods  
end  
end  
A.go.wibble  
A.new.wibble

The objects returned by these two calls are both instances of class A,  
but one has singleton methods added. This has some consequences - in  
particular, objects with a singleton class cannot be serialised using  
Marshal.dump

You don’t get that problem if you just return an instance of a different  
class:

class A  
class SoupedUp \< A  
def method\_missing(\*args)  
puts “method\_missing: #{args.inspect}”  
end  
end  
def A.go  
SoupedUp.new  
end  
end  
A.go.wibble # instance of A::SoupedUp  
A.new.wibble # instance of A

HTH,

Brian.

---

<div class="post-metadata">

**Author:** ![hunt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/71e660/32.png) [@hunt](https://www.ruby-forum.com/u/hunt)\
**Post date:** [July 28, 2009, 7:34am UTC](https://www.ruby-forum.com/t/query/172753/4 "2009-07-28T07:34:35Z")

</div>

Fabian S. wrote:

> hi, try this:
> 
> class A  
> class \<\< self  
> def go  
> obj = A.new  
> def obj.method\_missing \*args  
> p ‘method missing’  
> end  
> obj  
> end  
> end  
> end
> 
> A.go.uiae  
> A.new.uiae
> 
> Greetz!

i checked this program was run the out put is  
akshat@-desktop:~/Ruby/meta\_class\_&_patanahi\_23\_july$ ruby test\_meta3.rb  
“method missing”  
test\_meta3.rb:14: undefined method `uia’ for #\<A:0xb7ca3944\>  
(NoMethodError)  
akshat@-desktop:~/Ruby/meta\_class_&\_patanahi\_23\_july$

---

<div class="post-metadata">

**Author:** ![hunt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/71e660/32.png) [@hunt](https://www.ruby-forum.com/u/hunt)\
**Post date:** [July 27, 2009, 3:31pm UTC](https://www.ruby-forum.com/t/query/172753/5 "2009-07-27T15:31:41Z")

</div>

Hi –

On Mon, 27 Jul 2009, Hunt H. wrote:

> puts in methodmissing  
> If you don’t get a syntax error there, you’ve got a very strange  
> version of Ruby installed 🙂

> now when i create an object
> 
> A.new.add # it also prints in method missing & add method is missing.
> 
> which i don’t want I want that class method go which return an instance  
> should call method\_missing not an instance which is created  
> by A.new
> 
> how am i supposed to do?

Ruby provides a full toolkit for making two objects of the same class  
behave differently from each other. (In fact, classes are really just  
a convenient way to save writing code when you’ve got multiple objects  
that happen to share behaviors.)

Here’s what you can do:

class A  
module SpecialMethodMissing  
def method\_missing( method\_name)  
puts “in methodmissing”  
puts " #{method\_name} method is missing"  
end  
end

def self.go  
A.new.extend(SpecialMethodMissing)  
end  
end

I’m using extend to add the special method\_missing behavior (via the  
module) to that one instance.

Depending on the structure of the rest of your program, you might want  
to subclass A and have a different class whose instances have that  
special method\_missing.

David

---

<div class="post-metadata">

**Author:** ![hunt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/71e660/32.png) [@hunt](https://www.ruby-forum.com/u/hunt)\
**Post date:** [July 28, 2009, 12:42pm UTC](https://www.ruby-forum.com/t/query/172753/6 "2009-07-28T12:42:21Z")

</div>

well, that’s what you described.  
objects created with A.go have a method missing, objects  
created with A.new don’t.  
So calling A.go.uiae will execute method\_missing,  
calling A.new.uiae will result in an error, since there is no uiae  
method.

Greetz