From: Joel VanderWerf <vjoel@...>
Date: 2004-05-26T08:52:04+09:00
Subject: Re: $SAFE idiom (Re: defining condititions)

nobu.nokada@softhome.net wrote:
> Hi,
> 
> At Wed, 26 May 2004 08:13:25 +0900,
> Joel VanderWerf wrote in [ruby-talk:101419]:
> 
>>>You don't need save $SAFE, which is always thread local.  And,
>>>Proc also preserves its $SAFE value.  Though this was an
>>>unofficial feature in 1.6, guaranteed from 1.8.
>>
>>Hm. Didn't know that. Also, methods preserve $SAFE:
>>
>>def foo; $SAFE=3; end
>># => nil
>>$SAFE
>># => 0
>>foo
>># => 3
>>$SAFE
>># => 0
> 
> 
> Do you mean Method object?
> 
>   $ ruby19 -ve 'def foo;$SAFE=3;$SAFE;end;p method(:foo).call;p $SAFE'
>   ruby 1.9.0 (2004-05-25) [i686-linux]
>   3
>   0
> 
>   $ ruby19 -ve 'def foo;$SAFE=3;$SAFE;end;p foo;p $SAFE'
>   ruby 1.9.0 (2004-05-25) [i686-linux]
>   3
>   3
> 
>   $ ruby18 -ve 'def foo;$SAFE=3;$SAFE;end;p foo;p $SAFE'
>   ruby 1.8.2 (2004-05-24) [i686-linux]
>   3
>   3
> 

I was confused by irb:

$ irb
irb(main):001:0> def foo; $SAFE=3; end; foo; $SAFE
=> 3
irb(main):002:0> $SAFE
=> 0
irb(main):003:0> $SAFE = 3
=> 3
irb(main):002:0> $SAFE
=> 0

So it is really irb that is saving and restoring $SAFE around each input 
line. Maybe this is because irb is wrapping the input into a Proc.