From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2002-01-19T05:19:02+09:00
Subject: Re: dynamic method creation

In article <3C4878FE.F0D83753@uark.edu>,
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.  Below is my current best
>shot.  Is there a better way? If methods allowed expressions as
>names, and not just as qualifiers, I wouldn't need the eval.

A couple of questions about your example....

>
>class Record
>	def initialize(name)
>		@name = name
>	end	
>end
>
>fieldNames = ['abc', 'dof', 'ghi']
>fieldTypes = ['String', 'Fixnum', 'Float']
>rec = Record.new('aRecord')
>class << rec 
>end
 ^^^
This 'end' is probably not supposed to be here, right?

>fieldNames.size.times do | i |
>	f = fieldNames[i]
>	defStr = "def rec.#{f}=(obj)\n" 
>	case fieldTypes[i]
>		when 'String'		then defStr << "@#{f} = obj\n"
>		when 'Fixnum'		then defStr << "@#{f} = obj\n" 
>		when 'Float'		then defStr << "@#{f} = obj\n"
>	end
What is the purpose of this 'case' statement?  All branches seem to do the 
same thing - am I missing something?

>	defStr << "end\n"
>	puts defStr
>	eval defStr
Maybe it's better to use instance_eval?

>end
 ^^^
I suspect that this 'end' is the one that corresponds to the 
class << rec above (?)

>p rec.abc=(nil)
>p rec.dof=(nil)
>p rec.ghi=(nil)
>p rec.methods

I can't come up with another way that doesn't use some kind of eval to do 
this.

Phil