From: Hugh Sasse Staff Elec Eng <hgs@...>
Date: 2005-01-27T21:28:58+09:00
Subject: Re: When little languages grow...

On Thu, 27 Jan 2005, Dave Burt wrote:

> "ts" <decoux@moulon.inra.fr> wrote:
>>>>>>> "H" == Hugh Sasse Staff Elec Eng <hgs@dmu.ac.uk> writes:
>>
>> H>          Thread.new(input){|source|
>> H>            $SAFE=5
>> H>            instance_eval source
>> H>          }.value
>>
>> Sorry to say this but this is the most common error that I see when
>> someone try to eval some code with $SAFE >= 4
>>
>> The code will be eval'ed with $SAFE >= 4 but the result (#value) will be
>> used with $SAFE = 0 and you can have problems.
>>
>> The result of #eval must be cleaned with $SAFE >= 4, before it's
>> returned.
>
> Hi,
>
> I'm having trouble understanding what you mean by this. Can you say it in
> Ruby?

My understanding is

               valid_input = Thread.new(input){|source|
                  $SAFE=5
                  result = instance_eval source
                  final_result = validate(result)
                }.value

would be better than:

               result = Thread.new(input){|source|
                  $SAFE=5
                  result = instance_eval source
                }.value
                final_result = validate(result)  # OOPS!!!

because the validation takes places while "the safety catch is on"
in the first of these two cases.
>
> Cheers,
> Dave
>
         Hugh