# Define\_method confusery **URL:** \ **Category:** ruby-talk\ **Created:** [28 September 2006 16:09 UTC](https://rubytalk.org/t/define-method-confusery/31426 "2006-09-28T16:09:12Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Martin\_Coxall1](https://avatars.discourse-cdn.com/v4/letter/m/f475e1/32.png) [@Martin\_Coxall1](https://rubytalk.org/u/Martin_Coxall1)\ **Post date:** [28 September 2006 16:09 UTC](https://rubytalk.org/t/define-method-confusery/31426/1 "2006-09-28T16:09:12Z")
So I have some code which adds a method to a class based on user input like this: > **···** > > ---------------------------------------------------------------- > > class Klass > # Do nowt originally > end > > # Get the name of a method to add > puts "Enter the name of the method to add" > $stdout.flush > > methodName = gets > methodName.chomp! > > puts "Adding method #{methodName}" > $stdout.flush > > # Add a method called 'methodName' to Klass > Klass.class\_eval do >   define\_method(methodName) do |\*values| >     puts "Welcome to #{methodName}!" >     puts values.to\_s >   end > end > > # Try to invoke the new method > instance = Klass.new > instance.send(methodName, "---", "+++") > > # List the methods of Klass > Klass.methods.sort.each do |method| >   puts "Klass##{methodName}" > end > > ---------------------------------------------------------------- > > So, the code appears to work fine, in that the send() method is able to call > the newly created method. So, does anyone know why is it when I list the > methods of the class Klass afterwards, the new method does not appear? > > Also, is it possible to use define\_method() to add class methods to classes, > rather than just instance methods? I can't seem to get it to work. > > Regards, > > Martin ---
**Author:** ![Arnaud\_Bergeron](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Arnaud\_Bergeron](https://rubytalk.org/u/Arnaud_Bergeron)\ **Post date:** [28 September 2006 16:15 UTC](https://rubytalk.org/t/define-method-confusery/31426/2 "2006-09-28T16:15:15Z")
[snip] > # List the methods of Klass > Klass.methods.sort.each do |method| Try Klass.instance\_methods. > **···** > > On 9/28/06, Martin Coxall \ wrote: > > >   puts "Klass##{methodName}" > > end > > > > ---------------------------------------------------------------- ---
**Author:** ![Martin\_Coxall1](https://avatars.discourse-cdn.com/v4/letter/m/f475e1/32.png) [@Martin\_Coxall1](https://rubytalk.org/u/Martin_Coxall1)\ **Post date:** [28 September 2006 16:22 UTC](https://rubytalk.org/t/define-method-confusery/31426/3 "2006-09-28T16:22:01Z")
Aha! That would do it. Thanks. Do you know if it's possible to add class methods to classes using define\_method() then? It seems to work if I do a define\_method("Klass."+methodName) However, when I then try to invoke using Klass.send(methodName, "some stuff") It doesn't work. Regards, Martin > **···** > > On 9/28/06, Arnaud Bergeron \ wrote: > > > On 9/28/06, Martin Coxall \ wrote: > > [snip] > > \> > > \> # List the methods of Klass > > \> Klass.methods.sort.each do |method| > > > > Try Klass.instance\_methods. ---
**Author:** ![Rick\_DeNatale1](https://avatars.discourse-cdn.com/v4/letter/r/bbce88/32.png) [@Rick\_DeNatale1](https://rubytalk.org/u/Rick_DeNatale1)\ **Post date:** [28 September 2006 21:30 UTC](https://rubytalk.org/t/define-method-confusery/31426/4 "2006-09-28T21:30:56Z")
You need to send define\_method to the classes singleton class, and that takes a trick: rick@frodo:/public/rubyscripts$ cat def\_class\_meth.rb #! /usr/bin/ruby > **···** > > On 9/28/06, Martin Coxall \ wrote: > > > On 9/28/06, Arnaud Bergeron \ wrote: > > \> > > \> On 9/28/06, Martin Coxall \ wrote: > > \> [snip] > > \> \> > > \> \> # List the methods of Klass > > \> \> Klass.methods.sort.each do |method| > > \> > > \> Try Klass.instance\_methods. > > > > Aha! That would do it. Thanks. > > > > Do you know if it's possible to add class methods to classes using > > define\_method() then? It seems to work if I do a > > > > define\_method("Klass."+methodName) > > > > However, when I then try to invoke using > > > > Klass.send(methodName, "some stuff") > > > > It doesn't work. > > # > > def create\_method(name, klazz, meth = nil, &b) >   raise ArgumentError "give method or block, but not both" if meth && > block\_given? >   if block\_given? >     klazz.send(:define\_method, name, &b) >   else >     klazz.send(:define\_method, name, meth) >   end > end > > def create\_class\_method(name, klazz, meth=nil, &b) >   klazz\_klazz = class \<\< klazz; self; end >   create\_method(name, klazz\_klazz, meth, &b) > end > > class Foo > end > > create\_method(:foo\_inst\_meth, Foo) {"This is an instance method of Foo"} > create\_class\_method(:foo\_class\_meth, Foo) {"This is a class method of Foo"} > > puts Foo.new.foo\_inst\_meth > puts Foo.foo\_class\_meth > > rick@frodo:/public/rubyscripts$ ruby def\_class\_meth.rb > def\_class\_meth.rb:5: warning: parenthesize argument(s) for future version > This is an instance method of Foo > This is a class method of Foo > rick@frodo:/public/rubyscripts$ > > Note that in ruby 1.9 send won't call a private method anymore, you > need to use funcall instead. > [http://eigenclass.org/hiki.rb?Changes+in+Ruby+1.9#l18](http://eigenclass.org/hiki.rb?Changes+in+Ruby+1.9#l18) > > -- > Rick DeNatale > > My blog on Ruby > [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![Martin\_Coxall1](https://avatars.discourse-cdn.com/v4/letter/m/f475e1/32.png) [@Martin\_Coxall1](https://rubytalk.org/u/Martin_Coxall1)\ **Post date:** [28 September 2006 22:36 UTC](https://rubytalk.org/t/define-method-confusery/31426/5 "2006-09-28T22:36:03Z")
> You need to send define\_method to the classes singleton class, and > that takes a trick: Okay, I think I understand why that is, but I'd better re-read Programming Ruby on Singleton classes. > def create\_class\_method(name, klazz, meth=nil, &b) > klazz\_klazz = class \<\< klazz; self; end > create\_method(name, klazz\_klazz, meth, &b) > end Okay, I can kind of see that. I think. Um. Thanks very much. Martin