Re: set vs copy?
Re: set vs copy?
- Subject: Re: set vs copy?
- From: Alex Zavatone <email@hidden>
- Date: Tue, 14 Sep 2010 18:08:25 -0500
Try it with list values.
On Sep 14, 2010, at 6:05 PM, Bruce Robertson wrote:
> I tried to create an example but it didn't work. Maybe you can provide a variation that does illustrate the difference?
>
> Set A to "A"
> Set B to A
> Copy A to C
> Set A to "B"
> {B, C}
>
> -- result: {"A", "A"}
> -- thought it shoulda been {"B", "A"}
>
>
> On Sep 14, 2010, at 3:38 PM, Shane Stanley wrote:
>
>> On 15/9/10 7:01 AM, "tom wible" <email@hidden> wrote:
>>
>>>> For paranoia's sake, I used copy, but I'm sure a set will do the
>>>> trick.
>>>
>>> i've never seen a satisfactory explanation of exactly what a/s is
>>> doing in set vs copy...
>>
>> Copy makes a complete copy of what a variable refers to, whereas set just
>> makes another variable pointing to the same stuff in memory.
>>
>> For mutable classes like list, record and date, having more than one
>> variable point to the same chunk of memory means that if you modify the
>> contents of one of these variables, any others pointing to the same chunk of
>> memory will also return the new value. This can be avoided, where necessary,
>> by using copy to make an entirely separate, um, copy.
>>
>> For immutable classes like text, real, etc, the fact that more than one
>> variable can point to the same chunk of memory is irrelevant, because the
>> contents can't be modified once it's created anyway. So doing a copy in such
>> cases is just wasting time and memory.
>>
>> --
>> Shane Stanley <email@hidden>
>>
>>
>>
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