From: Joel VanderWerf <vjoel@...>
Date: 2006-11-12T04:02:12+09:00
Subject: Re: eval question

Peter Szinek wrote:
> Hi,
> 
> I am setting up a few variables based on user input with the following
> code snippet:
> 
> ==================================
> vars = %w{a b c}
> 
> vars.each do |var|
>   print "#{var} = "
>   val = gets
>   eval("$#{var}=#{val.chomp}")
> end
> 
> #use a, b, c here for something
> ==================================
> 
> What I don't like about this code is the use of global variables.
> However, I have to use them - or otherwise a,b,c will be already out of
> scope at the place I need them.

Use a hash?

vars = {
   "a" => nil,
   "b" => nil,
   "c" => nil,
}

def get_input vars
   vars.keys.each do |var|
     print "#{var} = "
     val = gets
     vars[var] = val.chomp
     eval("$#{var}=#{val.chomp}")
   end
end

get_input vars
p vars
__END__
a = 1
b = 2
c = 3
{"a"=>"1", "b"=>"2", "c"=>"3"}


You can use instance_eval with the hash, as you suggested:

module AcessibleKeys
   def method_missing(m, *rest)
     if rest.empty?
       fetch(m.to_s)
     else
       super
     end
   end
end

vars.extend AcessibleKeys

get_input vars
p vars

vars.instance_eval do
   puts "a+b+c = #{a+b+c}"
end
__END__
a = 1
b = 2
c = 3
{"a"=>"1", "b"=>"2", "c"=>"3"}
a+b+c = 123

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407