From: theschof@... (TheSchof)
Date: 2002-01-19T08:19:18+09:00
Subject: Re: dynamic method creation

"Albert L. Wagner" alwagner@uark.edu wrote:
>I have a need to dynamically create methods with method names
>that are not known until run time. 

Someone already mentioned this, but instance_eval really is your best bet for
actually creating methods.  The advantage of it is that when you combine that
with ruby's sophisticated string interpolation you can get code which will look
very close to how it will appear.  But you have to be comfortable with string
interpolation if you are going to be dealing with strings inside of this which
also will need to undergo interpolation.  I had this a while back when I was
working on a ruby-java bridge via via Tcl-blend-- it wasn't as complicated as
it sounds.  But it had a JObject class which took in a string as the
fully-qualified name of a Java class, and then used tclblends reflection
capabilites to grab a list of the methods for that class, and declare them for
each instance like so:

instance_eval "def #{met} (*args)
    if block_given?
        yield \"#{met}\", @tclhandle, args
    else
        $tcl.eval \"#{@tclhandle} #{met} #\{args.join ' '}\"
    end
end"

I was getting excited about this but I started to realize that maybe creating
methods was the wrong approach and method_missing would have been better and
provided more encapsulation in case a Ruby object had the same method name as a
java object.  If you're reading in strings you could intern them, use them as
the keys for a hash table and compose Proc objects for their values.   Use
method_missing to catch them and just look up the symbol in the hashtable and
call its Proc object (passing along any arguments).  I was starting to think
along those lines myself but then Jan Arne Petersen released a really fantastic
 JRuby interpreter, and no one had expressed any interest in my fledgeling
project so I abandoned it and can't tell you from experience how well this
would work in practice, but I can't think of a fault in the theory right now.

HTH,
Alexander Schofield