Re: [boost] [submission] STL-compliant containers with copy-on-write

Subject: Re: [boost] [submission] STL-compliant containers with copy-on-write
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2011-03-31 18:45:50

On Thu, Mar 31, 2011 at 2:07 PM, Jeremy Maitin-Shepard
<jeremy_at_[hidden]>wrote:

> On 03/31/2011 01:48 PM, Alexandr Sterligov wrote:
>
>> Yes, sorry... I will be more careful with calling anything STL-compliant.
>> It
>> is only STL-like.
>>
>
> It seems that using a generic COW wrapper might be more suitable.
> Internally it would maintain a pointer to a reference-counted instance of
> the base type.  It would provide a method for getting a const reference to
> the type (e.g. get(), operator*() and operator->()), and also a method for
> obtaining a non-const reference to a unique copy of the type (e.g.
> get_unique()), which would take care of copying if the reference count is
> greater than 1.
>
> I believe this interface is better than a specialized type that tries to
> mimic the interface of a particular container because generally if there is
> a need to mutate the type, it will be done by a series of possibly many
> mutating operations on the type/iterations, and it is inefficient to check
> if there is a need to copy e.g. on each iterator dereference or on each
> invocation of operator[].
>
> It also avoids the need to create the specialized types in the first place;
> a single quite simple wrapper type will solve the problem for all types.
>

+1; I believe this had been mentioned before by someone during the XInt
review, but I appreciate being reminded of this technique.

- Jeff