Re: [boost] Re: copy_on_write

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-06-01 16:03:53

Alexander Terekhov wrote:
> Peter Dimov wrote:
>>
>> Alexander Terekhov wrote:
>>
>>> Yeah, simply put, mutations of std::string object may invalidate
>>> references and iterators (with COW inspired semantics for non-
>>> const operator[]() et al. )... threads or no threads, COW or no
>>> COW.
>>
>> Umm, not exactly.
>>
>> int x = s[0];
>>
>> (with non-const s) does not invalidate if COW isn't used,
>
> Uhmm, that's not what the standard says.

I know what the standard says. ;-) It's still true. An uncounted string, a 
vector<> and an ordinary array do not invalidate and do not "write" when the 
above is used. COW is visible because it changes the semantics of a 
"non-const read".

My point was that a COW-friendly class should have had

class cow_friendly_string
{
public:

    char get( int i ) const;
    void set( int i, char ch );
};

sidestepping the above problem.