From: furtive.clown@...
Date: 2007-11-09T00:25:17+09:00
Subject: local variables, eval, and parsing


I read through posts like this

http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/18c16150d26df98e/ee9c34c590b2f316?lnk=st&q=ruby+eval+local_variables#ee9c34c590b2f316

http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/fd399f1d82be73a8/4c0df13f35d7e6fb?lnk=st&q=ruby+eval+local#4c0df13f35d7e6fb

but was still not satisfied with the solutions given.  For example

   val = nil
   eval "val = 12"
   p val

The mention of 'val' twice is a maintenance problem, as you need to
manually update the local variables in code whenever the variables
inside the string change.

   val = nil  # forgot to update -- manual labor is hard work
   eval "first_val = 12 ; second_val = 44"  # string has changed
   p first_val  # oops!

One solution is to change those locals into attributes of the
singleton:

def locals_to_accessors(str)
   previous_locals = local_variables
   eval str

   (local_variables - previous_locals).each { |name|
      value = eval name
      eval %Q{
         class << self
            attr_accessor :#{name}
         end
      }
      self.send("#{name}=", value)
   }
end

locals_to_accessors %q{
   val = 12
   foo = "bar"
}

# no errors!
p val
p foo

This seems like a gymnastic workaround.  All I want to do insert some
local variables from a config file.  Is there really no way to do that?