Re: [boost] [smart ptr] Any interest in copy-on-write pointer for C++11?

Subject: Re: [boost] [smart ptr] Any interest in copy-on-write pointer for C++11?
From: Jeffrey Yasskin (jyasskin_at_[hidden])
Date: 2013-02-08 16:44:24

On Feb 8, 2013 12:29 PM, "Mathias Gaunard" <mathias.gaunard_at_[hidden]>
wrote:
>
> On 08/02/13 18:35, Jeffrey Yasskin wrote:
>>
>> WebKit has a class vaguely like this for your case #2:
>>
https://code.google.com/p/chromium/codesearch/#chrome/src/third_party/WebKit/Source/WebCore/rendering/style/DataRef.h
>> used at
https://code.google.com/p/chromium/codesearch/#chrome/src/third_party/WebKit/Source/WebCore/rendering/style/RenderStyle.h&rcl=1360310731&l=137
.
>> Semantically every copy is a real copy, and, contrary to Mathias'
>> assertion, couldn't be replaced by a move in C++11, but they want to
>> share identical values when doing so is cheap.
>
>
> If you want identical values to use the same resource, you should use a
flyweight factory.
>

I'm sure the WebKit project would welcome a patch demonstrating that
flyweights are a more efficient technique for CSS matching. I don't expect
they are because these values are built up through several mutations, and a
hash table lookup plus a copy on each mutation sounds more expensive than
the current copy-on-write system.

Jeffrey