From: Sean O'Dell <sean@...>
Date: 2004-07-03T05:20:01+09:00
Subject: Re: define_method to add a Class method?

On Friday 02 July 2004 13:02, walter@mwsewall.com wrote:
> > On Friday 02 July 2004 12:42, walter@mwsewall.com wrote:
> > > How do you use define_method (or an equivalent) to add a method to a
> > > Class.
> > >
> > > I want to create a class from a Database result set at runtime.  I
> > > was doing this by building a string and the evaling it, which works,
> > > but wasn't all that rubyish and was ugly.
> > >
> > > I am now using an Anonymous class ie Class.new{...} and everything
> > > is great except I can't seem to create a class method this way.
> > >
> > > I know I am missing something quite obvious, I just can't seem to
> > > find it.
> > >
> > > Any pointers would be greatly appreciated.
> >
> > I'd stick with eval; it does the job.  Something like this should work
> > just fine:
> >
> > class_name = "MyClass"
> > code = "print 'Hello, world!\n'"
> > method_name = "my_method"
> >
> > eval_string = <<-EVAL
> >   class #{class_name}
> >     def #{method_name}
> >       #{code}
> >     end
> >   end
> > EVAL
> >
> > eval eval_string
> >
> > o = MyClass.new
> > o.my_method #=> "Hello, world!\n"
> >
> >
> >  Sean O'Dell
>
> That was how original version worked, and I can seem to port
> everything except the creation of the class methods using the
> Class.new{...} syntax.  It just seems as if I am missing something.
> Can we not add a class method using define_method.  I have tried it
> in combination with instance_eval, module_eval, directly on the
> class, within the class, etc but so far no luck.
>
> I guess I just want to know if it can be done using a define_ method
> or do we _have_ to use eval to add a class method this way.

Well, I can add a method to that same class I created with an eval, this way:

class MyClass
  define_method(:my_method2) do
    print("Hello, world, again!\n")
  end
end

o.my_method2 #=> "Hello, world, again!\n"


	Sean O'Dell