From: Robert Klemme <bob.news@...>
Date: 2004-02-02T02:29:53+09:00
Subject: Re: check whether a class is defined, listing all classes


"David Garamond" <lists@zara.6.isreserved.com> schrieb im Newsbeitrag
news:401D1FF4.6000900@zara.6.isreserved.com...
> ts wrote:
> >>>>>>"D" == David Garamond <lists@zara.6.isreserved.com> writes:
> > D> Hm, I should've added that I didn't want to involve 'eval'. But then
why
> > D> not, I'll just need to check the input using a simple regexp.
> >
> >  well, if you think that a simple regexp can do anything against the
evil
> >  eval, then you have perhaps a P background :-)
>
> Don't you also have a P background? :)  (Or Matz? Or many others?)
>
>   http://www.google.com/search?num=100&q=guy+decoux+perl
>
> Anyway, I didn't say regexp can make eval safe generally, but only for
> my case:
>
>   def class_defined?(classname)
>     classname.kind_of? String or
>       raise ArgumentError, "please give me string"
>     classname =~ /\A[A-Z][A-Za-z0-9_]*(::[A-Z][A-Za-z0-9_]*)*\z/ or
>       raise ArgumentError, "invalid class name"
>     eval("defined? " + classname) != nil

You don't need to compare with nil, that's converting something to a boolean
that is essentially a boolean already - unless, of course, if you want to
hide the outcome of "defined?"...

To make the methods semantic match the name you should do

eval("defined? " + classname) && Class === eval(classname)

Because otherwise you will get true for all sorts of constants. (Try with
"IO::CREAT")

>   end
>
> Please do tell me if the above is unsafe...

Looks safe enough.

    robert