From: Eric Hodel <drbrain@...7.net>
Date: 2005-10-21T05:13:09+09:00
Subject: Re: DbC, const and freeze.

On Oct 20, 2005, at 7:40 AM, Robert Klemme wrote:

> 2005/10/20, Ryan Leavengood <leavengood@gmail.com>:
>
>> On 10/19/05, John Carter <john.carter@tait.co.nz> wrote:
>>
>>> For example, look at this hole...
>>> irb
>>> irb(main):001:0> a = [[1,2],[3,4]]
>>> => [[1, 2], [3, 4]]
>>> irb(main):002:0> a.freeze
>>> => [[1, 2], [3, 4]]
>>> irb(main):003:0> a << [9]
>>> RuntimeError: can't modify frozen array
>>>         from (irb):3:in `<<'
>>>         from (irb):3
>>>         from :0
>>> irb(main):004:0> a[0]<<1
>>> => [1, 2, 1]
>>> irb(main):005:0> a
>>> => [[1, 2, 1], [3, 4]]
>>> irb(main):006:0>
>>>
>>> Even though "a" was frozen, I still could modify the things "a"  
>>> contained.
>>>
>>
>> Fair enough. How about this:
>>
> <snip/>
>
> Apart from the fact that deep_unfreeze is missing...

No, its not (well, you don't get the original back).

Marshal.load(Marshal.dump(obj))

> I still think that the concept of constness doesn't fit Ruby well.
> There are too many places where you can fiddle with state where you
> normally (i.e. in other PL's) aren't allowed to.  Adding #unfreeze
> wouldn't help either because it would break the contract of freeze
> that is used today - IOW code may break.

Of course, Marshal.load(Marshal.dump(obj)) works for regular unfreeze  
as well.

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
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