Re: [boost] [string] proposal

Subject: Re: [boost] [string] proposal
From: Dave Abrahams (dave_at_[hidden])
Date: 2011-01-21 14:56:07

At Sat, 22 Jan 2011 03:40:44 +0800,
Dean Michael Berris wrote:
> 
> On Sat, Jan 22, 2011 at 3:18 AM, Dave Abrahams <dave_at_[hidden]> wrote:
> > At Sat, 22 Jan 2011 01:56:36 +0800,
> > Dean Michael Berris wrote:
> >>
> >> No changing arbitrary content in the string. Concatenation is a
> >> process of creating new strings.
> >
> > But you're allowing assignment. Â That's not acting "as if it's const,
> > with no way to modify the string"
> >
> 
> Unless you frame assignment in terms of a "move".
> 
>   x = "This is the original";
>   x = "Not anymore";
> 
> What's happening here is that you're really making x refer to a
> different string. In essence, x is what you might call a proxy. You
> can change what the proxy refers to, but what it refers to you cannot
> change -- if that makes any sense. If you're reading or dealing with
> x, basically you're dealing with the proxy.

Sorry, no, that's not value semantics.  Value semantics are a subset
of Stepanov's "Regular Type" concept.  See EOP.

Let me be clear: when you assign into x, you are modifying its value.
If that can happen when x is const, x doesn't have proper value
semantics.  Implementation details like underlying buffers and
refcounting are irrelevant.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com