From: avi@...4.com (Avi Bryant)
Date: 2002-04-05T07:12:57+09:00
Subject: Re: Is eval a code/design smell?

harryo@zip.com.au (Harry Ohlsen) wrote in message news:<ff13c63f.0204032355.273be366@posting.google.com>...

> In this particular case, we're not doing a general eval, either,
> but a couple of instance_eval calls, to allow the
> serialise/deserialise to work with classes that may wish to restrict
> access to some of their attributes (for example, if the programmer
> wants some attribute to be read-only because it's a derived value,
> or for some other reason).

<snip>

> I think it was you who pointed to this being something that perhaps
> the language should be providing support for.  That would be even
> nicer, but isn't there right now, so far as I know.

Hmm, I don't think it was me - after all, the language *does* provide
support for this.  It's called instance_eval.  Now, what it doesn't do
is provide a nicely named method for it, but that's easy to add:

class Object
  def set_inst_var(name, value)
    instance_eval "..."
  end
end

I dunno exactly what magic you're using inside that instance_eval, so
I'll leave that up to you.  But my point is, as long as you
encapsulate it cleanly, the actual use of eval shouldn't be a code
smell to anyone but matz.