From: Robert Klemme <bob.news@...>
Date: 2005-10-21T05:36:59+09:00
Subject: Re: DbC, const and freeze.

Eric Hodel <drbrain@segment7.net> wrote:
> 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 meant, it's missing from the sample implementation.  But: Marshal does 
something completely different: creating a copy is something different from 
temporary freezing an instance's (or instance graph's) state.  It starts 
with different identities and doesn't stop at performance...  You *can* use 
that in certain scenarios but I doubt that it's a full replacement for 
constness.

Kind regards

    robert