Re: eval / toliteral safety question

• Date: Tue, 11 Jun 1996 14:17:15 PDT
• From:
  Don Schwarz <darkowl@darkowl.pr.mcs.net>
• Reply-to:
  darkowl@mcs.net
• cc: Chuck Adams <cadams@weather.brockport.edu>, "Seth I. Rich" <sir@po.cwru.edu>, MOO-Cows.PARC@xerox.com
• Content-Type: TEXT/PLAIN; charset=US-ASCII
• In-Reply-to: <199606111852.OAA21971@rabbit.INS.CWRU.Edu>

On Tue, 11 Jun 1996, Seth I. Rich wrote:

> Chuck Adams responds to me:
> 
> >> Is there EVER a circumstace where
> >>   eval("return " + toliteral(x) + ";")[2]
> >> would not equal x?  Can anyone think of a situation in which this would
> >> represent an unsafe operation?  I've been trying to think of a value for
> >> x for which this expression could have side effects, but I haven't come
> >> up with anything yet, and I suspect I won't.
> 
> >I can't think of anything, but why do you want an identity function?
> 
> Well, I don't want an identity function really.  I want a verb of the form:
> 
>   {start} = args;                 /* start = args[1] */
>   start = toliteral(start);       /* turn start into a string */
>   [...]                           /* do things to start which I can */
>                                   /*   guarantee to be safe */
>   return eval("return " + start + ";")[2];
> 
> For example, say you want to change "Xythian" to "HunkaHunkaBurningLove" within
> a string or a list of strings, or basically anywhere it exists within a
> variable.  I could do some awkward recursive thing, or just:
>   return eval("return " + strsub(toliteral(args[1]),
>     "Xythian", "HunkaHunkaBurningLove", 1) + ";")[2];
> 
As far as I can tell, that should work fine.  But if Xythian and
HunkaHunkaBurningLove aren't going to be hard coded into the verb you should
probably run them through toliteral() too.  For example:

  {start, search, replace} = args;
  return eval(tostr("return ", strsub(toliteral(start), toliteral(search),
         toliteral(replace)), ";"))[2];
                                               --Dark_Owl

• Re: eval / toliteral safety question
• From: "Seth I. Rich" <sir@po.cwru.edu>

• Prev: Re: eval / toliteral safety question
• Next: Re: eval / toliteral safety question
• Index: MOO-cows
• Thread: MOO-cows